Large Scale Solar Generation - personal.ee.surrey.ac.uk

Large Scale Solar Generation 14 – Jan – 2011

Group i

MDDP

2010-11 Large Scale Solar Generation

14th Janurary 2011

Callum Baines Ahmed Dahir Helen Flory

Richard Joules Kimberley Tapfumaneyi Muhamad Talib

University of Surrey

Guildford


ii

Executive Summary

From this report it has been confirmed that solar power can directly compete with the current

commercial energy market. The use of a solar chimney, also known as a solar updraft tower, is the

future of commercially available, cheap, solar power in the South East of the UK

The challenges to overcome in today‟s energy market are the continually rising price of oil, the

associated costs of constructing traditional combustion plants and that the UK Government is

legally required to reduce carbon emissions by 80% before 2050 (starting in 1990)(1). The solar

plant suggested combats all of these difficult challenges, steering away from future issues in to a

greener world.

The unit cost of electricity using this method is 10.6 pence/kWh. The price includes a short term

storage method that allows supply to be met 24 hours a day regardless of the availability of

sunlight. In comparison with the current competitive market price of a newly constructed coal

power plant the best unit cost the plant can offer ranges between 10-13 pence/kWh (MOTT). This

is how our plant competes with the open energy market.

Currently electricity is a necessity opposed to a luxury as it was 150 years ago. In the present day

it is used on every continent and every registered household in the UK is supplied with electricity.

The average person uses 1500 kWh/annum at a competitive cost of 13 pence/kWh. With the

population of the UK currently at 62 million the total market is worth £1.2 billion per annum. The

potential rewards of investing in a renewable solar power plant is very attractive to potential

investors, sizeable profits could be made as the price of energy from oil and gas increase.

A solar updraft tower is not affected by carbon emission taxes and has almost zero carbon

emissions over the operational life design life. This plant will be the first Solar Chimney to be

constructed in Europe. This pioneering project will develop the design and skill base in the UK

for constructing solar chimneys. This makes the chimney favourable in the eyes of the UK

government developing potential improvements in the British economy. A solar chimney such as

this has other political advantages, particularly it‟s accessibility for countries of all financial

positions, as unlike oil which is geographically restricted, electricity through solar power can be

generated anywhere in the world.

The report develops four methods of solar power generation and refines methods which perform

the best both financially and practically in the World today. The development of the system takes

into account an appreciation of the materials, location, construction and the environmental issues.

Different methods of storage and scales of production were analysed producing the optimum and


iii

most economic method of supplying a village of 2000 with a competitively priced unit of

electricity.

The system generates enough electricity in the winter to meet the demand and through the use of

short term (24 hour) storage, the system is completely self sufficient during the worst case daily

irradiance for solar power generation. During the summer months there is a surplus of electricity

and therefore after the required storage capacity for the night is achieved during daylight hours,

the surplus is exported and sold to the national grid at 11.5 pence/kWh to make profit.

The design of the system allows for the large collector area to be used for additional purposes

which can bring in extra revenue to the project. The uses for the area under the canopy have been

detailed within the report and proposed revenue from the various activities has been calculated.

Uses under the canopy include small buildings, sports grounds and agricultural land (both for

grazing and growing crops). The growing of crops would be a lucrative venture as the canopy acts

as a large green house, creating a controlled environment.

As previously stated the levelised cost of this method of power generation is 10.6 pence/kWh. The

return after 40 years would be £15.3 million as profit. The initial investment required is £33.8

million so the project can be constructed, including the construction of the short term daily

storage facility. The solar chimney does have potential to exceed the design life, dependant on the

local environment, of up to 70 years. This would reduce the levelised cost further however is not

guaranteed. Operational and maintenance costs are £428,800 per annum which have been

accounted for in the calculation of the levelised cost of 10.6 pence/kWh.


iv

Contents

1 Introduction ......................................................................................................................... 1

2 Concept ............................................................................................................................... 1

3 Constraints .......................................................................................................................... 2

3.1 Geographical................................................................................................................ 2

3.1.1 Altitude ................................................................................................................ 3

3.1.2 Geological ............................................................................................................ 3

3.1.3 Ground Temperature ............................................................................................ 3

3.1.4 Solar Irradiance .................................................................................................... 4

3.2 Environmental Concerns .............................................................................................. 6

3.3 Domestic Energy Constraints ....................................................................................... 7

3.4 Financial ...................................................................................................................... 8

3.4.1 Feed-in Tariffs ..................................................................................................... 8

3.4.2 Green energy certificate...................................................................................... 10

3.4.3 Competitive Electricity Pricing ........................................................................... 11

3.4.4 Inflation Analysis ............................................................................................... 12

4 Areas of study ................................................................................................................... 13

4.1 Generation ................................................................................................................. 13

4.1.1 Photovoltaic ....................................................................................................... 13

4.1.2 Solar Chimney ................................................................................................... 26

4.1.3 Solar Towers ...................................................................................................... 42

4.1.4 Solar Troughs ..................................................................................................... 54

4.2 Storage ...................................................................................................................... 67

4.2.1 Short Term Storage ............................................................................................ 67

4.2.2 Seasonal Storage ................................................................................................ 81

5 Analysis ............................................................................................................................ 92

5.1 Generation ................................................................................................................. 92

5.2 Storage ...................................................................................................................... 94

5.2.1 Short Term ......................................................................................................... 94


v

5.2.2 Seasonal ............................................................................................................. 96

5.3 Complete System ....................................................................................................... 98

6 Discussion ....................................................................................................................... 100

7 Conclusions ..................................................................................................................... 100

8 Recommendations ........................................................................................................... 104

9 Bibliography.................................................................................................................... 106

10 Appendix ..................................................................................................................... 115

10.1 Solar Chimney ......................................................................................................... 115

10.1.1 Derivation of turbine efficiency ........................................................................ 115

10.1.2 Design and Cost of Solar Chimney Construction .............................................. 115

10.1.3 Solar Chimney Collector for use as a Sports Facility ......................................... 115

10.1.4 Solar Chimney Collector for use as commercial greenhouse rental .................... 115

10.1.5 Costing associated with solar collector ............................................................. 117

10.2 Alternatives ............................................................................................................. 118

10.3 Solar Tower Power Plant .......................................................................................... 119

10.3.1 Table of Values for Solar Tower ....................................................................... 119

10.4 Short Term Storage .................................................................................................. 125

10.4.1 The Service life of PbA and other components in the system (50), (86) ............. 125

10.4.2 Annual capital costs for the solar chimney battery options (62), (63) ................. 125

10.4.3 Annual operating costs for the solar chimney batteries options (64) .................. 126

10.5 Seasonal Storage ...................................................................................................... 126

10.5.1 Graph to show discharge hours for seasonal storage .......................................... 126

10.5.2 Table to show calculation of seasonal storage capacity ..................................... 127

10.5.3 Map of Ringmer and proposed seasonal storage location .................................. 128


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List of Figures

Figure 1- BGS map showing heat flow from the ground. All the maps have been slightly edited to

show the boundaries of SE England (excluding London) (3) . ...................................................... 2

Figure 2 - Map to show horizontal solar irradiance variation across Europe as of 2006 ................ 4

Figure 3 - Average hourly solar irradiance for Hurn, UK from PVGIS and the Met Office ........... 5

Figure 4 - Graph to show average daily variation in solar irradiance ............................................ 6

Figure 5 - Estimated annual electrical requirements for a village of 2,000 from 2000 to 2050

showing a high demand and low demand estimate ....................................................................... 7

Figure 6 - Hourly domestic electrical demand per capita per season for the UK as of 2007 (10) ... 8

Figure 7 - Estimated domestic electricity cost in pence per kWh for the period 2006-2050 ......... 11

Figure 8 – UK inflation history and predictions for 2003 to 2014 with best and worst case

scenarios and government targets ............................................................................................. 12

Figure 9 -The effect of Temperature on the performance of the PV Cells ................................... 16

Figure 10 - Maximum available output per day (kWh/m2/day) over 12 months .......................... 17

Figure 11 - Plant Peak Output (kW) vs. PV cell area for various types of PV cells ..................... 17

Figure 12 - Layout of South facing solar panels on flat land with a 30° tilt ................................. 21

Figure 13 - Proposed layouts for the rows of solar panels ........................................................... 22

Figure 14 - Land Area & Cost requirements for Scenario B ....................................................... 23

Figure 15: Diagram of a hybrid solar panel (Greenemeier 2009) ................................................ 26

Figure 16 - Basic design of a single vertical axis turbine solar chimney shown top down and side

view and illustration of air flow through the system ................................................................... 27

Figure 17 - Basic design of collector framework to support transparent roofing ......................... 28

Figure 18 - Top (left) and side (right) view of inlet vane guides for vertically mounted turbines

used to inprove efficency of turbine and support chimney .......................................................... 31

Figure 19 - Comparison of observed power output from Manzanares solar chimney prototype to

simulated results for Manzanares prototype ............................................................................... 32

Figure 20 - Variation in model error over a range of transmission coefficients and turbine

efficiency to show sensitivity of model ...................................................................................... 33

Figure 21 - Graph to show power production over the course of a year for a plant situated near

Portsmouth against annual demand for a village of 2000 for scenarios A, B and C .................... 37

Figure 22 - Effect of variation in solar irradiance on levelised cost and annual electrical

production for scenario A, B and C ............................................................................................ 38

Figure 23 - Cumulative profit before inflation and tax for hot house renting and sports facility

busininess constructed in the solar chimney collector................................................................. 40

Figure 24 - Possible distribution of collector land space for use with business ............................ 40


vii

Figure 25 - Cash flow before tax and in real terms for a solar chimney plant with and without

additional revenue sources such as hot house renting and sports facilities .................................. 42

Figure 26- a diagram showing how STPP works ........................................................................ 43

Figure 27 – common heliostat layout for optimising spacing and avoiding overshadowing (38) . 47

Figure 28 - Power output for different scenarios using water as a working fluid ......................... 49

Figure 29 - Hourly power output for different scenarios using molten nitrate salt as a working

fluid .......................................................................................................................................... 49

Figure 30 – Annual power output from the STPP and electricity demand for 2000 people .......... 50

Figure 31- simulation to determine the size of heat exchangers and pump .................................. 51

Figure 32- to determine the amount of air required as well as the size of receiver ....................... 51

Figure 33 - Cumulative cash flow of solar tower investment ...................................................... 53

Figure 34 - Ariel view of the solar power stations SEGS III to VII (Solar Electric Generating

Systems), KJC, Kramer Junction, California, with an installed capacity of 30MW each Invalid

source specified. ........................................................................................................................ 55

Figure 35 - The solar thermal power system .............................................................................. 55

Figure 36 - Typical solar field of parabolic trough solar collector (44) ....................................... 56

Figure 37 - Absorber tube (44) .................................................................................................. 56

Figure 38 - Sample of 2-D view Invalid source specified. and 3-D view heat absorber element .. 56

Figure 39 - Heat transfer fluids (HTF) and their properties (102) ............................................... 57

Figure 40 - Extended solar trough with Storage Invalid source specified. ................................... 58

Figure 41 - Collector efficiency for various absorber tube diameter Invalid source specified. ..... 60

Figure 42 - Thermal Efficiency graph versus collector temperature above ambient (35) ............. 60

Figure 43 - Solar trough efficiency by demonstrated and projected (47) ..................................... 61

Figure 44 - Power (Wh) demands and generate from the model ................................................. 63

Figure 45 - Daily average power output Wh/month with new change -increase the total area of

solar collector = 80,000m2 ......................................................................................................... 63

Figure 46: Operation & Maintain ace (O&M) cost over the power generates (46) ...................... 65

Figure 47 - Levelised energy cost (46) ....................................................................................... 65

Figure 48 - Solar trough model cash flow .................................................................................. 66

Figure 49 - PV-battery system components and life cycle (51) ................................................... 70

Figure 50: Lithium ion battery ................................................................................................... 71

Figure 51 - Shows the winter production of the PV plant and demand curves per household ...... 75

Figure 52 - Histogram of monthly heat injection and heat extraction. Taken from (67) ............... 83

Figure 53 - Graph to show optimal capacities and discharge periods for a range of commercially

available electricity storage methods. (68) ................................................................................. 84

Figure 54 - A representaion of the process of a hydr-electric pumped storage system (75) .......... 86


viii

Figure 55 - Optimum turbine choice varying with net head and discharge rate through the turbine

(76) ........................................................................................................................................... 89

Figure 56 - Arrangement of turbines to regulate the output/input flow (74) ................................ 89

Figure 57 - Map of Ringmer, Sussex and surrounding geography showing proposed location of

the upper storage reservoir and extent of reservoir walls. Taken and adapted from appendix

11.5.3. ....................................................................................................................................... 90

Figure 58 - Cost estimates for francis turbines vs flow rate for 50m head (81) ............................ 91

Figure 59 - Histogram to show total cost of a pumped hydro storage facility for a year periof .... 97

Figure 60 - Graph to show the effect of increasing the design life on levelised cost .................... 97

Figure 61 - Histogram to show the total cost of storage for scenario generation discussed in

4.1.1.9 and 4.1.2.5 ..................................................................................................................... 98

Figure 62 - Effect of variation in life span on levelised cost for a solar chimney power plant...... 99

Figure 63 – Area of collector available for use with agriculture................................................ 116

Figure 64 - Basic financial information for solar chimney with and without additional revenue

sources .................................................................................................................................... 117

Figure 65 - The development of PV Technology (Lawrence Kazmerski 2010) ......................... 118


ix

List of Tables

Table 1 - Altitude heights ............................................................................................................ 3

Table 2 - Breakdown of solrr irradiance values for Hurn, UK 2009 .............................................. 5

Table 3 - Table of Feed-in Tariff levels for April 2010 for different generation methods (REF) ... 9

Table 4 - General Data on Types of PV cells (20) (21) (16) ....................................................... 15

Table 5 - Increase and decrease temperature effects on solar PV cells (20) (16) ......................... 15

Table 6 - Capital Costs (22) (23)................................................................................................ 18

Table 7 - Maintenance Costs (20) (16) ....................................................................................... 19

Table 8 - Total Life Costs per m2 for a PV plant using various cell types ................................... 19

Table 9 - General Data and Calculated Figures .......................................................................... 20

Table 10 - Normalised Total Cost over the Design Life for different PV cells ............................ 20

Table 11 - Table of three different scenarios to compare affect on levelised cost ........................ 22

Table 12 - Manzanares solar chimney prototype plant specification and observed environmental

values ........................................................................................................................................ 31

Table 13 - Material properties for solar collector roofing and ground surface type...................... 34

Table 14 - Comparison of Solar Chimney Plant Outputs and Costs if constructed in Portsmouth to

find most feasible for a village of 2000 ...................................................................................... 37

Table 15 - Table comparing dimensions and costs for solar chimney plants producing same annual

outputs in Portsmouth and Bedford ............................................................................................ 41

Table 16 - Solar tower power plant efficiency values ................................................................. 44

Table 17- constants used to calculate receiver efficiency ............................................................ 46

Table 18 - hourly power output in June ...................................................................................... 47

Table 19 – Solar Tower power plant capable of meeting the needs of a village of 2,000 with

additional storage required ........................................................................................................ 49

Table 20 - annual and peak projected efficiencies of STPP based on various system configurations

(33) ........................................................................................................................................... 50

Table 21 - levelised cost for different scenarios ......................................................................... 52

Table 22 - The total system efficiency analysis from studies, SEGS VI project and the calculation

................................................................................................................................................. 61

Table 23 - Estimated area values for solar trough collector and comples .................................... 62

Table 24 - Costing values for a solar trough power plant including capital and OM ................... 64

Table 25 : Final value calculate ................................................................................................. 67

Table 26 - Description of the common batteries used (51), (52), (53), (54) ................................. 70

Table 27 - Annual capital costs for the PV plant battery options (62), (63), ................................ 78

Table 28 - Annual operating costs for the PV plant batteries options (64), (63) .......................... 79

Table 29: Summary for the solar chimney and PV plant PbA battery storage ............................. 79


x

Table 30 - Summary table of PbA worst case annual costs and life cycle cost for the solar

chimney .................................................................................................................................... 80

Table 31 - Summary table of annual costs of running lead acid and the life cycle cost for the PV

system (worst case..................................................................................................................... 80

Table 32 - Table to show calculation of seasonal storage requirement to support the solar chimney

generation method ..................................................................................................................... 87

Table 33 - Table to show long term storage requirements.......................................................... 88

Table 34 - Comparison of electrical generation methods comparing key features of each based on

new builds starting after 2009 (17) ............................................................................................ 92

Table 35 - Cost of land plot for each method of solar generation and its effect on levelised cost . 93

Table 36 - NPV values for various methods of generation and their associated discount rate ...... 94

Table 37 - Corrected service life for PbA for the PV application ................................................ 95

Table 38 - Basic capital cost for each sports facilitie ................................................................ 115

Table 39 - Basic costs per square meter for agricultural renting business equipment................. 116


xi

Abbreviations

AC Alternating Current

a-Si Amorphous Silicon

BGS British Geological Society

BST British Summer Time

CAES Compressed Air Energy Storage

CCL Climate Change Levy

CdTe Cadmium Telluride

CFD Computational Fluid Dynamics

CIGS Copper Indium Gallium Selenide

DC Direct Current

DOD Depth of Charge

EIA Environmental Investigation Agency

FIT Feed In Tariffs

GWh Giga Watt (1,000,000,000 Watts)

HCE Heat Collecting Elements

HGF Heat Transfer Fluid

IVG Inlet Vane Guide

kW Kilo Watt (1,000 Watts)

LEC Levy Exception Certificates

m-Si Monocrystalline Silicon

MW Mega Watt (1,000,000 Watts)

NiMH, NiCd Nickel Alloy Batteries

NPV Net Present Value

OM Operation and Maintenance

p Pence

p-Si Polycrystalline Silicon

PETE Proton Enhanced Thermionic Emission

PV Photovoltaic

PVGIS Photovoltaic Geographical Information System

REGO Renewable Energy Guarantee of Origin

ROC Renewables Obligation Certificate

SMES Super Conducting Energy Storage

SOC State of Charge

STPP Solar Tower Power Plant

TSO The Stationary Office


xii

UK United Kingdom

UTES Underground Thermal Energy Storage

W Watt (1 Watt)

Wh Watt Hours


xiii

Nomenclature

Symbols:

A Area (m2)

Cp Specific heat capacity (J / Kg K)

g Acceleration due to gravity ~9.81 m/s2

G Local Solar Irradiance (kWh/m2)

H Height (m)

P Power (W)

T Temperature (K)

Q Energy input for heat gain in the collector (W)

Subscript:

abs Absolute

area Area

amb Ambient

av average

car (carnot) Refers to the Transfer Cycle in Solar Chimneys

cell Solar Cell

col Solar Chimney Collector

cost economical

chim Solar Chimney Chimney

e Solar

gain Increase

he Heat Exchange

in Input

Max Maximum

opt Optimum

out Output

plant Total System (whole plant)

power Power

R Receiver

rec Required

T total

tot total

track Solar Tracking System


xiv

turb Turbines

Greek Symbols:

α effective absorption coefficient (mean product of storage absorbivity and

collector roof transmission)

β Thermal loss coefficient (W/m2)

Δ Change in

ε Emissivity

σ Boltzmann‟s Constant

φ Flux

η Efficiency


Group 1

1 Introduction

As technology progresses solar energy is becoming a more feasible method of electrical

generation. In 2007, only 7% of the UK consumed domestic electricity was from renewable

sources (2). With the rising cost of fossil fuels and increase in public awareness of environmental

issues solar energy is becoming more of a focus. Solar energy is a renewable generation method

and releases minimal pollution during its use period; however it is very dependant on location.

This report aims to investigate the feasibility of using solar generation as a means of energy

supply for a small village in the South East of the UK. The solar generation technologies are

proven to work, however this is generally in hot areas under test conditions. It is unclear whether

solar generation is financially feasible or technologically viable with in a region renowned for its

gloomy weather.

This report will evaluate the technology involved, the British climate and topography within the

South East and the costs incurred in relation to solar generation. This report evaluates four of the

most promising forms of solar generation under a range of conditions and considers the

requirements, costs and yields for each to power a village of 2,000. Other considerations when

evaluating feasibility will be the external requirements for each form of generation such as

storage, maintenance and durability.

This report investigates and compares a range of generation scenarios, considering geographical

and social requirements, cost and yield to evaluate the feasibility of solar generation within the

South East of the UK. The most feasible of the methods are evaluated in greater depth in order to

arrive at a recommendation for the feasibility of solar generation for the UK.

2 Concept

The aim of this project is to evaluate the feasibility of using solar power to generate a proportion

or all of the power requirements for a village of 2000. Due to the limitation on content length and

time allotted for this project, the scope has been refined to investigating the feasibility of

supplying the needs of domestic electrical energy only. It is impractical to consider the

commercial electrical requirements of a village due to the vast variation in requirements and

report limitations. The investigation of using solar energy for water and space heating was also

deemed impractical due to the same limitations involved in this report.

The key constraints affecting the method of generation will be the topography and size of the area

required the solar irradiance available in that area, domestic electrical demand and the normalised

cost of that method of generation.


2

Group | 3.1 KimT

The key areas of study will be generation methods, namely Photovoltaic (PV), Solar Chimneys,

Concentrated Solar Towers and Parabolic Troughs as these are the most widely publicised and

successful forms for solar generation. Other relevant areas of study will be domestic electrical

usage, electrical pricing trends, solar irradiance distribution, environmental concerns and energy

storage methods. These will be required to make a more informed evaluation on the feasibility of

solar generation for a village of 2000 in the South East of the UK.

This report aims to deliver an in depth evaluation of the feasibility of using solar power to

generate electricity for a village of 2,000 in the South East of the UK; delivering an in depth

financial and practical appraisal of solar generation.

3 Constraints

There are many factors constraining the performance and cost of solar generation technology,

these are expounded below.

3.1 Geographical

The composition of the ground and geographical locations determines where the technology

should be built. If there is not a suitable location the technology would not be feasible in SE

England. Issues such as altitude, geological profile, aquifers and ground temperature have been

considered in order to determine a suitable site for the plant. The geology affects the generation

technologies, as discussed in section 4.1.2.4, as well as the large term storage methods.

The South East, as depicted in Figure 1, has an abundance of both flat and rolling terrain, the type

of terrain is largely determined by the general location within the South East. The variation in

terrain will cater for the geographical requirement of most generation and storage systems.

Figure 1- BGS map showing heat flow from the ground. All the maps have been slightly edited to show the

boundaries of SE England (excluding London)(3) .


3 3.1.1 | 3.1.2 | 3.1.3 Kim T

3.1.1 Altitude

The boundaries of South East England are shown in Figure 1, the highest levels in each county

was located and are represented in Table 1. These affect the potential locations for the storage and

generation technologies.

County Height (m) Location

Oxfordshire - -

Berkshire 297 West Berk, Walbury Hill

Buckinghamshire 267 Haddington Hill and Coombe Hill

Hampshire 286 Pilot hill

Surrey 295 Leith Hill near Dorking

Sussex 162, 248 Beachyhead, Ditching, Beacon(Downs)

Isle of Wight 241 Boniface Down

Table 1 - Altitude heights

3.1.2 Geological

The different types of surface geology in South East England are: Sandstone, Mudstone,

Limestone, Clay, Sand and Silt. This is based from geological maps from the British

Geographical Survey (BGS)(4). Both the surface and sub-surface geology will affect the

generation and storage feasibility.

The sub-surface geology will be considered to a depth of 600m in order to evaluate the feasibility

of under ground storage, namely Compressed Air Energy Storage (CAES) and Underground

Thermal Energy Storage (UTES) (5) as discussed in section 4.2.2. CAES and UTES are both

underground storage technologies requiring specific geological conditions. CAES stores energy as

high pressured air in an underground cavern and UTES uses the natural underground water to

store the energy. There are different geological formations that can be used for CAES and UTES

such as salt caverns, hard rock caverns or naturally occurring aquifers. Salt caverns and natural

aquifers are easier to locate as most of SE England ground is mainly limestone. Rock caverns are

more expensive to mine because the solid rock underground is excavated whereas salt caverns are

simply mined using a solution.

3.1.3 Ground Temperature

The surface of the earth is warmed up by the sun‟s radiation; the regional temperature can have

both positive and negative effects on generation depending on the technology used. Heat flow is

the measurement of conduction of heat above a surface. The heat flow is mostly from 0.04-0.06

W/m2, this is the normal rate across England. There is an exception which is Devon where the


4 3.1.4 Helen F

heat flow is 0.13 W/m2 because the ground has a high heat production due to the thermal

properties of granite which is abundant in that area.

3.1.4 Solar Irradiance

Solar irradiance is the term used to describe the amount of solar energy which may reach a

given area. Solar irradiance is measured in watts per square meter (W/m2) and is effectively

the power from the sun available per square meter. For the purpose of measuring solar

irradiance for the design of the solar generation unit, a decision must be taken as to the angle

in which the radiation is hitting it. Depending on the angle, additional components of solar

irradiation will contribute to the total solar irradiance which the instrument receives. As well

as the radiation which travels directly to the point and hits a flat surface on the earth, solar

radiation reflected off particles in the earth‟s atmosphere and objects on the earth‟s surface

will mean additional radiation from different angles must also be accounted for.

Figure 2 - Map to show horizontal solar irradiance variation across Europe as of 2006

There is a sizable range of different solar irradiance data available to researchers such as the

Met Office and The Photovoltaic Geographical Information System (PVGIS). PVGIS is a

database supported by the European Commission Joint Research Centre and provides a

comprehensive map of solar irradiance values for all locations in Europe. It provides the

variation in irradiance with the day in the year, the time of day and the angle at which the

irradiance is received. Figure 2 shows the variation in solar irradiance across the UK. From

this data alone it is evident that within the South East of England, the area experiencing the

highest solar irradiance levels is the South Coast. It would be most advantageous to locate the

potential solar generation site as far to the South West as is possible.


5

3.1.4 Helen F

The PVGIS data is based on both recorded irradiance values and a computed model. The

computed model takes the estimation of the overall energy absorbed by the earth from the sun

and applies factors to it: cloud cover, diffusion and height above sea level. The recorded

values come from 563 recording stations across Europe which recorded irradiance values with

time at a range of angles; as such some error must be accounted for. This error is only with

comparison to recorded values for just 563 stations across the whole of the European

continent. Further comparison of this data must be made with recorded values in the UK to

make it accountable.

The met office has an abundance of irradiance data for a range of locations in the South East.

Four data sets were obtained from the Met Office at Great Shelfin Farm in Hooe, Norwood

Place Farm, Herstmonceux in West End and Hurn which provided data both inland and on the

coast. When comparing these data sets with the PVGIS data set for the same Easting and

Northing, differences were found, particularly in the summer months. The annual variance

between PVGIS and the Met Office data is 5.2%. It is considered that the PVGIS data is more

reliable due to the fact that it has been averaged over 30 years; as such it will be favoured

over the Met Office data. The average hourly solar irradiance values for Hurn from the Met

Office and PVGIS over a year at the horizontal are shown in Figure 3 in order to illustrate the

annual irradiance trend as well as the variance between the data sets.

Figure 3 - Average hourly solar irradiance for Hurn,

UK from PVGIS and the Met Office

2009 Hourly Solar

Irradiance

(kW/m2)

Daily Solar

Irradiance

(kW/m2)

Monthly Solar

Irradiance

(kW/m2)

Av Temp

(°C)

Jan 0.037 0.884 27.410 4.0

Feb 0.059 1.424 39.870 4.5

Mar 0.134 3.221 99.860 6.5

April 0.180 4.320 129.590 9.5

May 0.229 5.501 170.520 12.5

June 0.254 6.090 188.780 16.0

July 0.217 5.205 156.140 18.0

Aug 0.178 4.266 132.250 17.0

Sept 0.145 3.473 107.660 15.0

Oct 0.072 1.728 53.580 11.0

Nov 0.043 1.026 30.780 7.5

Dec 0.031 0.737 22.840 5.5

Table 2 - Breakdown of solrr irradiance values for Hurn, UK

2009

0

50

100

150

200

250

300

Jan

Feb

Mar

ch

Ap

ril

May

Jun

e

July

Au

g

Sep

t

Oct

No

v

Dec

Ave

rage

Ho

url

y Ir

rad

ian

ce W

/m2

Months

PVGIS Met Office


6

3.1.4 | 3.2 Helen F

Figure 3 shows that the solar irradiance is much higher in summer compared to winter. This is

due to the orbit of the earth causing variation in proximity of the site to sun over the course of

the year; as such solar generation will have greater power generation potential in summer

compare to winter.

The daily variation in solar generation over a year period is shown in Figure 4, it is noted that

winter days are much shorter and have lower values of irradiance compared to summer days

which are significantly longer with higher irradiance, this will have a significant effect on

amount of power solar generation can deliver.

Figure 4 - Graph to show average daily variation in solar irradiance

3.2 Environmental Concerns

All major construction projects in the UK require an Environmental Impact Assessment

(EIA), in line with directive 97/11/EC, an amendment of the original 85/337/EEC. For this

project, the Habitats Directive (92/43/EEC) and the Wild Birds Directive (79/409/EEC)

should be considered (6) . The EIA is an important way in which the potential impacts can be

demonstrated to the public, with the aim of providing a systematic account of the likely

consequences of building a large scale solar power plant which could potentially consume

large areas of countryside. As such the effects of constructing power plants over large areas

should be discussed in relation to their environmental impact.

0

20

40

60

80

100

120

140

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

Irra

dia

nce

d k

Wh

Hourly


7

3.3 Richard J

3.3 Domestic Energy Constraints

To evaluate the feasibility of using solar power to supply a village of 2,000, it is necessary to

calculate the electrical energy required by that village. Using the domestic energy

consumption projections from (7) and the population trends from (8) the energy consumption

per capita have been estimated for the period 2010-2050, Figure 5. These estimations take

into account increased population, climate change and continued technological development

as well as government legislation such as the 2050 pathways report (9). A high demand and a

low demand projection were predicted based on possible future trends; the lower electricity

requirement projection assumes a reduction in CO2 emissions in line with government

proposals (9), more efficient home design and use of high efficiency appliances. The high

demand case of energy requirements is based on the assumption of demand following its

current trend combined with an increase in heating and cooling products due to climate

change and a society with a greater consumption of domestic technological goods (7). As

shown in Figure 5 the current average consumption per person is estimated ~1500kwh per

annum, this value is an approximation based on the total UK domestic consumption divided

by the estimated population at the time (3). Due to the lack of observed readings this value

may be subject to errors and should only be considered an approximation. These errors are

mainly due to the large quantity of unknown variables encountered when predicting future

population, technology and climate trends.

The electrical demand prediction shown in Figure 5 are the annual requirements, it is noted

that the demand over the year is not constant but will vary with the seasons based the amount

of daylight, average temperature and social habits. The observed seasonal demand per capita

is shown in Figure 6 (2).

Figure 5 - Estimated annual electrical requirements for a village of 2,000 from 2000 to 2050 showing a high demand and

low demand estimate

0

500

1000

1500

2000

2000

2002

2004

2006

2008

2010

2012

2014

2016

2018

2020

2022

2024

2026

2028

2030

2032

2034

2036

2038

2040

2042

2044

2046

2048

2050

Co

nsu

mp

tio

n (k

Wh

)

Year

High Demand

Low Demand

Mean Demand


8

3.3 Richard J | 3.4 | 3.4.1 Helen F

Figure 6 - Hourly domestic electrical demand per capita per season for the UK as of 2007 (10)

Winter is shown to have the highest electrical demand, with an average hourly demand of

221W/h this is likely due to the need for more artificial lighting and a tendency for people to

stay in more. Summer has the lowest demand with an average of 156W/h which is helped by

bright, warm days coupled with social habits. The seasons used in Figure 6 are defined as the

following based on the demand data in(10); spring is the period following the start of BST in

March to the start of summer commencing at the start of May. Summer lasts from May until

the Sunday after the English Bank Holiday in August. Autumn is defined as the period

starting a week after the last Monday in August and ending on the same day as BST ends in

October. Winter runs from the end of BST in October to the day before the start of BST in the

following year. It is noted that in seasons with lower solar irradiance demand is greater than

during seasons when there is a greater abundance of light, this will be a serious challenge

when designing a power plant dependant on sun light.

3.4 Financial

There are also financial constraints to be considered when evaluating solar generation. Any

future solar generation project will be affected by the price of competitive energy supply as

well as government policy and incentives; as such these will be investigated below.

3.4.1 Feed-in Tariffs

Feed in tariffs (FIT) were introduced by the UK government in April 2010 as a method of

encouraging investment into small renewable energy systems for homes and small businesses.

The FIT scheme pays a reward to investors in renewable generation based on the amount of

energy which they produce. This „tariff‟ applies to specific methods of renewable generation

only, as shown in Table 3. These are the main renewable energy generation methods used

with in the UK; different incentive rates apply to each method as shown by the tariff rates in

Table 3.

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

00:3

0

01:3

0

02:3

0

03:3

0

04:3

0

05:3

0

06:3

0

07:3

0

08:3

0

09:3

0

10:3

0

11:3

0

12:3

0

13:3

0

14:3

0

15:3

0

16:3

0

17:3

0

18:3

0

19:3

0

20:3

0

21:3

0

22:3

0

23:3

0

De

man

d (k

Wh

)

Time

Spring

Summer

Autumn

Winter


9

3.4.1 Helen F

Energy Source Scale Generation Tariff

(p/kWh)[A]

Duration (years)

Anaerobic digestion ≤500kW 11.5 20

>500kW 9 20

Hydro

≤15 kW 19.9 20

>15 - 100kW 17.8 20

>100kW - 2MW 11 20

2MW - 5MW 4.5 20

Micro-C P[B] <2 kW 10 10

Solar PV

≤4 kW new[C] 36.1 25

≤4 kW retrofit[ ] 41.3 25

>4-1 kW 36.1 25

>10 - 100kW 31 4 25

>100kW - MW 2 .3 25

Standalone[C] 29.3 25

Wind

≤1.5kW 34.5 20

>1.5 - 15kW 26.7 20

>15 - 100kW 24.1 20

100 500kW 18.8 20

>5 0kW - 1.5MW 9.4 20

>1.5MW - 5MW 4.5 0

Table 3 - Table of Feed-in Tariff levels for April 2010 for different generation methods (REF)

There are two tariffs which can be claimed for any generation system. One is a generation

tariff which is paid for every kW produced. An additional tariff can be claimed on top of the

generation tariff if the energy produced is sold back to the grid. This is currently at a rate of

3p/kW(11) and this price is applicable to all the above generation methods, unlike the

generation tariff.

The generation tariffs are available for a limited number of years as shown in Table 3. For a

new PV cell system of less than 4 kW the tariff is paid for 25 years from the year the tariff is

initialized. The generation tariff rate will be decreased based on the up-take in the scheme. To

ensure that this scheme benefits small renewable projects, there is a 5 MW cap on the size of

plant this scheme will support. This was put in place to prevent large established energy

companies from taking advantage of the funding.

In order to claim feed-in tariffs, wind turbines or photovoltaic cells must pass certain

requirements. All new generation installations must have a „micro-generation certificate‟.

This was introduced as a way of maintaining standards for renewable energy systems in

domestic buildings in the same way that other utilities such as water and gas already do. This

is a step forward in regulating renewable technology; however this is limited to the main

renewable generation methods.


10

3.1.4 Helen F | 3.4.2 Ahmed D

The future of the FIT scheme remains uncertain after it was reviewed with the UK

governments Spending Review (2010)(12). No immediate changes have been made to the

FIT scheme however it was noted in the 2010 Spending Review:

“...the efficiency of Feed-In Tariffs will be improved at the next formal review, rebalancing

them in favour of more cost effective carbon abatement technologies. This will save £40

million in 2014-15. Support for lower value innovation and technology projects will also be

reduced, saving £70 million a year on average over the Spending Review period.”

The funds made available for the FIT will therefore inevitably be reduced in time and the

increased investment activity in renewable technology seen over the past year(13) could be

short lived.

3.4.2 Green energy certificate

To address the issue of climate change and fulfil a carbon reduction target, carbon charges

have been introduced in industries to encourage the reduction of emissions released into the

atmosphere. This direct taxation, the Climate Change Levy (CCL) is applied to all industries

and can have a significant effect on the profitability of a process unless action is taken to

reduce or capture carbon emissions. Currently the cost of carbon is £12/tonne (CRC, 2010).

Generators of renewable source of energy can claim three types of renewable energy

certificates which are Levy Exemption Certificates (LECs), Renewables Obligation

Certificates (ROC) and Renewable Energy Guarantee of Origin (REGOs) (Green energy

certificates, 2009). A badge is given to generators that meet the requirements which are

regulated by both Ofgem and HM Revenue and Customs. The LEC is issued for each

Megawatt hour that a generator produces; however, the electricity must be consumed in the

UK. As a result suppliers have to source sufficient LECs from generators, or face significant

charges.

There is a nominal value for the amount of taxation for which LECs can secure exemption;

this value is currently £4.41 per MWh. This charge would is passed to the business consumer

by the utility if it not exempted. Generators can now obtain money for each LEC from the

energy supplier to whom they sell their electricity. Payment for LECs is a matter between the

generator and supplier

For every 1MW of renewable electricity generated, generators of all sizes can claim 1 ROC.

In addition micro-generators can receive up to 1-2 ROCs per year depending on size and


11

3.4.3 Richard J

technology being used. Micro-generators could currently expect to receive approx £20-£30

per ROC, but this is subject to the market and is affected by various other factors (14)

3.4.3 Competitive Electricity Pricing

To evaluate the financial feasibility of the project over it is necessary to estimate the average

cost of electricity from domestic suppliers for the period of 2000-2050. These pricings will

indicate whether the cost of solar generation can competitively compete with other forms of

generation. For 2010 the average domestic electricity price was given at 12.99p/kWh (6) in

order for solar energy to be feasible the price of the electricity generated must be competitive

with this value.

The price of domestic electricity is shown to approximately follow the same trend as global

fuel costs (ref). In the UK the majority of electricity used is generated by coal (~40%), gas

(~30%) and nuclear (~20%) with a small contribution from oil and renewable sources (1).

These ratios will change continuously based on the costs of the fuels use, where the cheaper

fuel will be used at an increased rate to meet demand. Using the projected fuel costs from

2000-2050 as predicted in (7) and the ratio of generation methods shown in (1); a prediction

of domestic energy price trends has been formulated, Figure 7. This prediction will be taken

as an approximation of future price trends and is based on real prices not inflated prices. The

main errors associated with this prediction are an assumption of the generation method

distribution ratios and the cost of fuel.

Figure 7 - Estimated domestic electricity cost in pence per kWh for the period 2006-2050

An upper and lower band of pricing was predicted in order to account for different future

eventualities. The upper values of the price prediction assume electrical generation continues

following the historic trend and generation source contributions remaining consistent. In this

0

2

4

6

8

10

12

14

16

18

20

2006

2008

2010

2012

2014

2016

2018

2020

2022

2024

2026

2028

2030

2032

2034

2036

2038

2040

2042

2044

2046

2048

2050

Co

st o

f El

ect

rici

ty (

p/k

Wh

)

Year

High Price

Low Price

Mean Price


12

3.4.3 Rich J | 3.4.4 Callum B

scenario prices fluctuate more due to the heavy dependency on coal and gas which have a

predicted price variation as discussed in (7); these prices increase due to the predicted

decrease in fossil fuel stocks. The lower price range follows the trend in generation set out by

the government policy of carbon emission reduction (4), this scenario assumes a move toward

increased nuclear generation and renewable sources, which have a relatively steady fuel cost

and a reduction in coal and gas generation methods which have a higher more varied price.

3.4.4 Inflation Analysis

Inflation is defined as a persistent increase in prices, triggered when demand for goods is

greater than the available supply (Morgan Stanley, 2010). The effect inflation has on the

energy prices in the UK based on this definition means that the price of energy increases

based on the demand. The data gathered in this section will be used as a part of predicting the

future energy prices and levelling the costs given from articles from previous years.

Inflation is not only very difficult to predict, economists are reluctant to comment on future

forecasts due to the uncertainty of world events. There are so many variables that influence

the inflation rates only crude and approximate predictions can be made.

The below chart, Figure 8, shows the actual historical inflation since November 2003 until the

end of 2010 with three predictions. The 12 month predictions are taken from the following

(15):

Figure 8 – UK inflation history and predictions for 2003 to 2014 with best and worst case scenarios and

government targets

UK Inflation Predictions (HM Treasurary)

0.00%

1.00%

2.00%

3.00%

4.00%

5.00%

6.00%

Nov-03 Nov-04 Nov-05 Nov-06 Nov-07 Nov-08 Nov-09 Nov-10 Nov-11 Nov-12 Nov-13 Nov-14

Date (Month)

Pe

rse

nta

ge

(%

)

Actual Government Target Lowest Highest


13

3.4.4 Callum B | 4 Group | 4.1.1 Callum B

The high prediction is based on the high point of the previous 10 years of inflation and the

lowest based on the low point. The government target trend is projected using a 2% base rate.

The historical inflation data can be used in the project to adjust the prices given from papers

written in previous years. These adjustments are used as a way of levelling the value of

money regardless of the year the price was taken from. As an example if a plant cost was

given as £10 million in 2005, it would now be worth £11,131,652.92 with an inflation average

of 2.9% per year.

The future predictions will be used as a means of predicting the future energy price increases.

These will be used when estimating a cost per kWh and a cost analysis over the design life of

the power structure.

4 Areas of study

In order to provide an in-depth evaluation of feasibility the methods of solar generation and

energy storage will be examined in detail, as discussed below.

4.1 Generation

This section will investigate different the methods of solar generation that can be used to

supply electricity to a village of 2,000. In order to effectively compare the financial feasibility

of each form of generation the levelised cost of generation will be calculated and compared.

The levelised cost is the real cost of every kWh produced based on the capital and Operation

and Maintenance costs (OM) over the lifetime of production. This value is normalised and

will allow for a fair comparison of different generation methods with different life spans and

capacities; it is not to be confused with the sale price per kWh which will be affected by

inflation and aimed at maximising profit whilst remaining competitive.

4.1.1 Photovoltaic

To determine the most suited method of generating electricity solar photovoltaic (PV)

generation is considered and evaluated as discussed below. Invented in 1958, PV electricity

generation uses the sun‟s rays to generate electricity. Photovoltaic solar cells use solar

irradiance to excite electrons across a band gap causing a flow of electricity. Although an

expensive method of production, especially when storing electricity, it is the most developed.

4.1.1.1 Types Chosen & Justification

Five leading types of solar photovoltaic cells have been selected, examined closely and

compared. A brief explanation of the reasons why they were selected is given below.


14

4.1.1.1 Callum B

Mono-crystalline Silicon (m-Si)

In order to produce a mono-crystalline silicon cell, pure high grade silicon is necessary,

mono-crystalline rods are then extracted from melted silicon and cleaved into thin wafers

(16). These are more efficient than polycrystalline silicon cells due to the purity of the

semiconducting material; however because of this they are also more expensive.

Poly-crystalline Silicon (p-Si)

In this process liquid silicon is poured into blocks that are subsequently split into wafers

during solidification of the material, crystal structures of varying sizes are formed, at whose

borders defects emerge (16). This reduces the material cost compared with m-Si, but the

efficiency is reduced as a consequence.

Amorphous Silicon (a-Si)

Amorphous Silicon is viewed as the most developed of the thin film technologies available.

Nearly 35% of the projected thin film capacity of 2010 is expected to be related to a-Si (17).

Amorphous Silicon uses much less material than m-Si and p-Si as the thin film is placed on

thin glass plates, this reduces the material costs significantly in comparison. However the

efficiency suffers because of this.

Copper Indium Gallium Selenide (CIGS)

CIGS is mainly used in photovoltaic cells (CIGS cells), in the form of polycrystalline thin

films. Unlike the silicon cells based on homo-junctions, the structure of CIGS cells is a more

complex hetero-junction system (18). CIGS is the most efficient of the methods examined and

as such has the highest output per meter squared.

Cadmium Telluride (CdTe)

CdTe PV technology has the smallest carbon footprint and fastest energy payback time of

current PV technologies when measured on a life cycle basis (16). Like with other thin film

methods less material is used and is coated onto glass, thus making it more economically

viable. The thickness of the films means that the amount of active material used is relatively

small; it has been estimated that even if CdTe solar cells were to provide more than 10% of

the world's energy requirements, this would still only account for less than a tenth of the

world's cadmium usage (19).


15

4.1.1.2 | 4.1.1.3 Callum B

4.1.1.2 Analysis of Types

Table 4 below gives the key parameters for the five selected methods of PV generation, with

the calculated output in kW/m2 given, the power output per unti area is calculated using

equation [1].

Thin Film Crystalline

Amorphous

Silicon

Copper Indium

Gallium

Selenide

Cadmium

Tellurium

Mono -

crystalline

Silicon

Poly -

crystalline

Silicon

(a-Si) (CIGS) (CdTe) (m-Si) (p-Si)

Efficiency (%) 6.9 13.8 10.9 22.9 17.3

(+/-0.3) (+/-0.6) (+/-0.5) (+/-0.5) (+/-0.5)

Area (m sq) 0.846 0.729 0.72 1.626 1.635

Weight (kg) 12.5 12.7 11.4 20 24

Output (W) 58 80 65 240 225

Output (W/m sq) 69 110 90 148 138

Output (kW/m sq) 0.069 0.11 0.09 0.148 0.138

Thickness (mm) - - 6.8 46 50

Table 4 - General Data on Types of PV cells (20)(21) (16)

4.1.1.3 Temperature Effects on Cells

The temperature effects on the PV cells are the displayed in Table 5 below. The effects of the

changes in temperature are based on a percentage decrease in performance, dependent on the

change in temperature above or below the optimum of 25°C.


Amorphous

Silicon

Copper

Indium

Gallium

Selenide

Cadmium

Tellurium

Mono -

crystalline

Silicon

Poly -

crystalline

Silicon

(a-Si) (CIGS) (CdTe) (M-Si) (P-Si)

Increase Temperature

Effect (%/°C) -0.22 -0.36 -0.25 -0.38 -0.48

Decreased Temperature

Effect (%/°C) -0.22 -0.36 -0.20 -0.38 -0.48

Table 5 - Increase and decrease temperature effects on solar PV cells (20)(16)

[1]


16

4.1.1.4 Callum B

Figure 9 -The effect of Temperature on the performance of the PV Cells

4.1.1.4 Annual Irradiance Effects

Below are the three equations used to determine the temperature modified maximum output

of the PV cells. These equations are used to plot Figure 10 which shows the changes (in the

maximum available output per meter squared, per day, over 12 months.)

[2]

This gives the usable solar power per meter squared per day.

for < Max Capacity

else

[3]

Where max capacity is the maximum power the cell is able to produce.

[4]

This equation shows the temperature modified maximum power output the PV is able to

produce in kW per day.

Temperature Effects on Thin Film Solar Photovoltaics

0.00

20.00

40.00

60.00

80.00

100.00

120.00

140.00

160.00

-5 0 5 10 15 20 25 30 35 40 45

Temperature (C)

Po

we

r O

utp

ut

(W

)

Amorphous Silicon Copper Indium Selenium Cadmium Tellurium Monocrystaline Silicon Polycrystaline Silicon


17

4.1.1.5 Callum B

Figure 10 - Maximum available output per day (kWh/m2/day) over 12 months

4.1.1.5 Modified Outputs

The modified output is the original maximum output when the temperature factors have been

taken into account. Figure 11 below shows the best and worst cases for each PV cell type

against the area required for that peak output to be produced. The worst cases use the average

temperature (4 degrees C) and the irradiance levels of December, whereas the best cases use

the average temperature (17 degrees C) and the irradiance levels of June.

Figure 11 - Plant Peak Output (kW) vs. PV cell area for various types of PV cells

Maximum Available Output over 12 Months

0.000

0.200

0.400

0.600

0.800

1.000

1.200

1.400

1.600

Jan-09 Feb-09 Mar-09 Apr-09 May-09 Jun-09 Jul-09 Aug-09 Sep-09 Oct-09 Nov-09 Dec-09

Month

Ou

tp

ut (

kW

h/

m s

q/

da

y)

Amorphous Silicon Copper Indium Selenium Cadmium Tellurium Monocrystalline Silicon Polycrystalline Silicon

Output vs. Area

0.000

1000.000

2000.000

3000.000

4000.000

5000.000

6000.000

7000.000

8000.000

9000.000

0 20 40 60 80 100 120 140 160 180 200

Thousands

Area (m sq)

Ou

tpu

t (k

W)

Mono (Worst Case) Mono (Best Case) Poly (Worst Case) Poly (Best Case) a-Si (Worst Case)

a-Si (Best Case) CdTe (Worst Case) CdTe (Best Case) CIGS (Worst Case) CIGS (Best Case)


18

4.1.1.6 | 4.1.1.6.1 | 4.1.1.6.2 Callum B

4.1.1.6 Costing

The cost of the system and construction is calculated in the below section. The prices

calculated are both in cost per kWh, total cost for a plant at max capacity per kW.

4.1.1.6.1 Capital Cost

The capital cost is given by the price (£) per Watt per PV module. To make this scalable a

price per square meter has been calculated based on the output of each type of solar PV cell

and the cell area, shown below in [5]. The capital cost also covers the costs involved in

construction.

[5]

This equation coverts the capital cost per unit power produced into cost per unit area, this will

allow for dynamic scaling of the plant and estimation of capital.

Type


Amorphous

Silicon

Copper

Indium

Gallium

Selenide

Cadmium

Tellurium

Mono -

crystalline

Silicon

Poly -

crystalline

Silicon


Capital Cost

(£/Watt) £0.96 £1.09 £1.22 £1.46 £1.16

Capital Cost

(£/kW) £960 £1,090 £1,220 £1,461 £1,159

Capital Cost (£/m2) £65.82 £119.62 £110.14 £215.65 £159.45

Table 6 - Capital Costs (22)(23)

4.1.1.6.2 Maintenance Cost

The maintenance and operational costs are taken from (20) and are calculated using the

equations shown below. The maintenance and operational costs for CIGS was not available so

the data used was for a CIS module. The costs were interpolated from table II in (20).

The maintenance cost is scaled by the annual cost per unit power combined with the overall

annual output per unit area. This gives the annual OM per unit area a price.

[6]


19

4.1.1.6.3 | 4.1.1.6.4 Callum B

Type


Amorphous

Silicon

Copper

Indium

Gallium

Selenide

Cadmium

Tellurium

Mono -

crystalline

Silicon

Poly -

crystalline

Silicon


Maintenance Cost

(£/Watt/year) £0.15 £0.16 £0.17 £0.19 £0.16

Maintenance Cost

(£/kW/year) £150 £160 £170 £187 £155

Maintenance Cost

(£/m2/year)

£10.28 £17.56 £15.35 £27.60 £21.32

Maintenance Cost 30

Year Life Span (£/m2)

£308.40 £526.80 £460.50 £828.00 £639.60

Table 7 - Maintenance Costs (20)(16)

4.1.1.6.3 Total Cost

The total cost of the plant takes into account the maintenance costs of the plant over the

design life using a cost per unit power of the total plant. The total cost is the Maintenance

costs added to the Capital costs. Table 8 below shows this and gives a total cost per meter

squared for each type of solar PV. The total life cost is defined as the sum of the capital

expenditure and the total OM over the 30 year life span of the PV plant.


Amorphous

Silicon

Copper Indium

Gallium

Selenide

Cadmium

Tellurium

Mono -

crystalline

Silicon

Poly -

crystalline

Silicon


Capital Cost (£/m2) £65.82 £119.62 £110.14 £215.65 £159.45

Maintenance Cost 30

Year (£/m2)

£308.40 £526.80 £460.50 £828.00 £639.60

Total Life Cost (£/m2) £374.22 £646.42 £570.64 £1043.65 £799.05

Table 8 - Total Life Costs per m2 for a PV plant using various cell types

4.1.1.6.4 Peak Plant Cost

With reference to part requiring a peak plant of 8220 kW, the size, capital, maintenance and

total cost of a solar PV plant this size are displayed in table x below. The boxes highlighted in

yellow indicate the lowest cost for that criterion.


20

4.1.1.6.5 Callum B


Amorphous

Silicon

Copper

Indium

Gallium

Selenide

Cadmium

Tellurium

Mono -

crystalline

Silicon

Poly -

crystalline

Silicon


Output (kWh/m2/Year) 78 156 124 253 191

Total Output Over Plant

Life (kWh/m2)

2336 4668 3713 7598 5737

Plant Area Required (m2) 39439 19720 24846 12284 16260

Capital Cost (£/m2) 65.82 119.62 110.14 215.65 159.45

Maintenance Cost 30 Year

Design Life (£/m2)

308.51 526.75 460.42 1,043.69 799.17

Capital Cost (£Mil) £2,595,874.98 £2,358,906.

40

£2,736,538.4

4

£2,649,044.6

0

£2,592,657.0

0

OM Cost (£Mil) £12,167,325.8

9

£10,387,51

0.00

£11,439,595.

32

£12,820,687.

96

£12,994,504.

20

Total Cost Over Life

(£Mil)

£14,763,200.8

7

£12,746,41

6.40

£14,176,133.

76

£15,469,732.

56

£15,587,161.

20

Capital Cost (£/kWh)

[Storage Mod] £3,244,843.73

£2,948,633.

00

£3,420,673.0

5

£3,311,305.7

5

£3,240,821.2

5

Total Cost Over Life

(£/kWh) [Storage Mod]

£18,454,001.0

9

£15,933,02

0.50

£17,720,167.

20

£19,337,165.

70

£19,483,951.

50

Table 9 - General Data and Calculated Figures

4.1.1.6.5 Levelised Cost

The levelised cost is calculated based on the design life of the plant. It is the total cost of the

plant divided by the power produced over the total design life, 30 years. This will show the

most financially viable type of PV cell which will then be used to design a PV plant for the

village.


Amorphous

Silicon

Copper

Indium

Gallium

Selenide

Cadmium

Tellurium

Mono -

crystalline

Silicon

Poly -

crystalline

Silicon


Output (kWh/m2/Year) 77.859 155.607 123.778 253.257 191.226

Total Output Over

Plant Life (kWh/m2)

2335.771 4668.205 3713.35 7597.709 5736.766

Capital Cost (£/kWh) £0.03 £0.03 £0.03 £0.03 £0.03

Levelised Cost (£/kWh) £0.16 £0.14 £0.16 £0.14 £0.14

Table 10 - Normalised Total Cost over the Design Life for different PV cells

From Table 10 above, the most financially viable PV cell is Polycrystalline Silicon, followed

closely by CIGS. This table shows that cost per kWh produced including capital and OM is


21

4.1.1.7 | 4.1.1.8 Callum B

lowest for P-Si, other cell types will have a slightly higher production cost which when scaled

up will have a large effect on the plant.

4.1.1.7 Modification for Short Term Storage

The demand for electricity does not follow the available output from the PV solar cells. Due

to this there will be times throughout each day when the demand exceeds the supply.

Therefore short term storage is required in order to meet the supply required over the night

time when there will be no output from the solar panels. The method of short term storage is

shown in 4.2.1 for PV solar storage.

In order to estimate the required area needed to produce such a plant, the losses due to storage

are required. These values will be used in combination with the preferred type of cell to

determine a method and capacity value of short term storage. The chosen method will have an

associated percentage loss that can then be used to modify the original output data to produce

a storage modified actual available output.

4.1.1.8 Panelling Configuration

A constant problem with fixed angle PV plants is overshadowing, panels arranged in close

proximity can cast shadows on neighbouring panels reducing production. This is most notable

when the sun is low on the horizon. The sun path in the South East of England reaches a low

of 15.1° from the horizontal at midday on the 21st December. This is the lowest angle and

therefore worst case for the rows of panels over shadowing each other, this means that he

minimum spacing can be calculated. Using simple trigonometry a minimum distance of

2.22m is recommended with the panels angled at 30° from the horizontal and south facing to

achieve the maximum output. Figure 12 below displays the layout.

Figure 12 - Layout of South facing solar panels on flat land with a 30° tilt

The panels can be set up in rows as long as the distances and angles in Figure 13 are adhered

to. The proposed layouts are dependant on the flat land available but three suggested sites are

detailed in Figure 13 below.


22

70

Rows

228.2m 193.6m

60

Rows

195.6m 225.8m

50

Rows

163.5m 271.0m

4.1.1.9 Callum B

In order to set the panels to achieve a desirable output, the method of connection needs to be

established. The output of solar panels in series gives a summation of the voltages of the

panels connected whilst current remains at the same level of a single panel. A parallel

connection of the panels will result in a summation of the current of all the connected panels

with a voltage level of a single panel. Solar panels generally provide low voltage and

relatively high current, through careful design of the panel connection the work load on the

inverter and transformer.

4.1.1.9 Scenarios table

In order to design an optimal PV plant, three main scenarios have been considered, these

scenarios where then compared to find the most financially feasible. Three separate methods

of approach have been detailed below and the table below refers to the criterion from each

method. A summary of the scenarios is given below, a full explanation of each scenario is

given in section 4.3.1.5.

A - Power Produced is used by the village and covers the whole in one year (fully

sustainable though storage)

B - Adequate output in winter with huge amounts in Summer (fully sustainable)

C - Adequate output in Summer, in winter power is bought from the national grid.

Scenario A B C

Average hourly Demand (kW/h) 362 443 310

Average hourly Production (kW/h) 362.6 1518 184

Area of Panels Required (m2) 16260 70000 8500

Peak Output (kW) 8220 35387 4297

Annual output (GWh) 3.11 13.37 1.62

Short Term Storage Max (kWh) 3258 3987 2790

Seasonal Storage (MWh) 1050 0 0

Initial Capital Cost (£l) £149,730,061.00 £11,178,536.00 £1,372,361.00

Average OM (£/Year) £1,190,637.84 £2,336,374.64 £1,025,194.64

Total Life Cost (£) £373,668,718.26 £120,784,929.26 £71,643,354.26

Levelised Cost (pence/kWh) 390 21.5 147

Table 11 - Table of three different scenarios to compare affect on levelised cost

Figure 13 - Proposed layouts for the rows of solar panels


23

4.1.1.10 Callum B

From Table 11 above the most financially viable scenario, based on levelised cost, is scenario

B. The levelised cost difference is significantly lower than the original scenario (A) therefore

this warrants changing the initial plan of the plant and storage. In addition although the total

life cost, initial capital cost and the average OM costs are lower for scenario C the levelised

cost is still higher due the decreased output of the plant.

4.1.1.10 Analysis

The irradiance variation both daily and annually means the plant production does not follow

the trend of demand. As a result both short and long term storage are needed when production

does not always exceed demand (Scenario A). Long term (seasonal) hydro electric storage is

to store surplus energy created during peak months and re-distribute it when supply cannot

need demand, see section 4.2.2. The short term storage is achieved using batteries, section

4.2.1. The addition of both short and long term storage significantly increases the cost of the

system from a levelised cost of 14p/kWh over life span to 390p/kWh (Scenario A).

The average annual output of the specified Polycrystalline PV solar cells is 3.197GWh, for a

panel area of 16,260m2. Using scenario B detailed in section 4.1.1.9 the annual output for a

70,000m2 plant gives an annual output of 13.37GWh with no seasonal storage. Finally

scenario C has an area of 8500m2 and produces an output of 1.62GWh per annum with no

seasonal storage and importing power for the winter deficit.

Requirements

Land area (including panel Spacing) 190,138 m squared

Cost - Capital (excluding storage) £11,161,500

Capital (including storage) £11,178,536.00

Total Life Cost £120,784,929.26

Levelised Cost per Kwh 21.5p/kWh

Figure 14 - Land Area & Cost requirements for Scenario B

The weather effects on PV solar panels are dependent on temperature, wind and precipitation.

Detailed in section 4.1.1.3 the temperature has a direct effect on the performance of each type

of PV cell. The optimum operating temperature for all PV solar panels is 25°C, with affects

on operation decreasing either side using a %/°C factor. The effect between the worst case

temperature and the optimum temperature for Polycrystalline Silicon is approximately 10%

loss in performance.

Large panels mean that wind loadings can make the panels act as a sail, requiring strong

fixings and good foundations. In addition to wind loadings, precipitation can have a large


24

4.1.1.11 | 4.1.1.12 Callum B

affect on the performance of the cells. Strong hail has a small chance of causing damage to

the panels, dependant on the strength of the storm. Snow fall can cover the surface of the

panels, reducing the potential output of the cells. The operational and maintenance costs may

need to be factored to account for scenarios such as these.

4.1.1.11 Further Considerations

To increase the potential output of the plant, the size of the plant would need to be increased.

The cost and size of the solar cells increase linearly with the output, as such a prediction of

the plant cost and area that can supply 20,000 people will be simple. The problem arises in

finding and purchasing the land suitable for a 167,200 squared meters of solar panels required

for this scaled up plant. There may be a reduction in cost based on increasing the size to this

scale however this would only be due to the amount of material required.

An investigation into the effects of using a solar tracking system will be an area of further

study. The data and calculations used in this study are taken from papers and specifications

that do not use tracking systems. The panels are positioned at the optimum angle of 30

degrees to from the horizontal in each with a bearing specific to the location of testing.

4.1.1.12 Complete System

The total efficiency of the completed structure is taken as the difference between the amount

of sunlight available and the amount that can be used by the customer. With this principle in

mind there is 81.2 GWh/annum irradiated over the 70,000 metres squared of solar panels. The

panels have efficiencies of 17.3±0.5% and after factoring loss due to temperature effects in

gives 13.4 GWh/annum. Further there are losses from the use of short term storage of 80% of

the power used from the batteries during hours of no sunlight. Combining the losses due to

the use of batteries and when the power is used directly gives an output of 12.1 GWh/annum.

Deducting 5% for general losses in the system and waste gives a total of 11.5 GWh/annum.

Converting this into a percentage of the total system results in a 14.1% overall efficiency.

The overall levelised cost of the complete system of Polycrystalline photovoltaic solar cells,

seasonal and 24 hour short term storage is £3.90 per kWh. Compared to designing a plant

with adequate power production during the winter months this is quite expensive, as a plant

such as this would have a levelised cost of £0.30 per kWh. This is due to no required seasonal

storage at a saving of £148,704,368 including maintenance.

The total life cost of the complete system, including 16,260 m squared of polycrystalline

silicon solar photovoltaic panels, short term storage in the from of batteries and seasonal


25

4.1.1.12 Callum B | 4.1.1.13 | 4.1.1.13.1 Kim T

storage from an artificial hydroelectric dam, is £373,668,718.26. This includes all operational

and maintenance costs over a 30 year life span for the panels and both storage systems.

However it was highlighted in section 4.1.1.9 that the most economically viable, in terms of

levelised cost, was scenario B. This uses 70,000 metres squared of solar panels, no long term

storage only 24 hour, short term storage. The total life cost of a system such as this is

£120,784,929.26 including operational and maintenance costs .

The total capital cost of the complete system is £149,730,061, however the capital cost of the

solar panels is £2,592,657. Therefore if a system was to be used that did not require seasonal

storage then the area would be 70,000 m squared (stated in section 4.1.1.9) and would have a

capital cost of £11,178,536 including short term, 24 hour storage.

The operational and maintenance for the storage is covered in the storage section 4.1.1.6.

4.1.1.13 PV Technology Enhancements

PV technology is continuously being subjected to research and development (R&D) to

improve conversion efficiency. This is because efficiency along side capital cost per watt

capacity defines the viability of PV power. This section briefly looks at the research on

improving PV technology rather than the different technologies available, and how they may

be relevant to the feasibility study. The most viable of the new concepts for PV enhancement

are

Photon Enhanced Thermionic Emission (PETE)

Hybrid Solar Panels Combined PV with Thermoelectricity

4.1.1.13.1 Photon Enhanced Thermionic Emission (PETE)

PETE is a process that converts solar energy and increases the efficiency of solar cells by

harnessing both light and heat from the sun, and maintaining the high temperatures that are

reached during conversion.

This process is a fusion of PV and thermal technologies and was developed by Stanford

University and SLAC National Accelerator Laboratory. It allows the normally wasted heated

accumulated during conversion to be used to generate electricity. These high temperatures in

normal conditions would cause silicon cells to degrade and lose efficiency. However, in this

process an added layer of caesium over the semiconducting material allows it to

simultaneously use the heat and light from the sun at high temperatures to produce electricity.

The cost of the technology is greatly reduced because it is simply an application to an existing

technology. The efficiency is calculated to be 55% to 60%, at least triple the existing systems


26

4.1.1.13.2 Kim T | 4.1.2 Richard J

(Alternative Energy 2010). Due to the lack of regular hot weather (>30⁰C) it is unlikely that

investment in this technology is worth while.

4.1.1.13.2 Hybrid Solar Panels Combined PV and Thermoelectricity

This Hybrid panel design is durable and combines PV cells and thermoelectric materials to

absorb the sun‟s energy to generate electricity and hot water for the house. Figure 15 shows

the design by Yin of the hybrid solar panel.

Figure 15: Diagram of a hybrid solar panel (Greenemeier 2009)

The outer layer is a protective cover. The PV layer converts the sun‟s radiation into

electricity, and the layer containing thermoelectric material uses the sun‟s heat to produce

electricity. The layer of plastic tubes which is the most important bit of the design, carry water

that cools down the PV layer when it starts to overheat. As the layer is cooled, heat is

absorbed by the water and this is then carried away and used in the house. The last layer at the

bottom is plastic lumber.

This prototype device is expected to have an efficiency of at least 12% compared to the low-

costing thin-film cells which is 5%-10% efficient. However, this efficiency is still low

compared to the more expensive and higher efficient solar cells. Although PV panels

integrated into buildings already exist, none of them have a TE layer in them. That is why this

could be a successful technology for the SE village because it produces both electric and

thermal power for the house.

4.1.2 Solar Chimney

Solar Chimneys or as they are also known, Solar Updraft Towers, use the heat energy from

the sun to induce convection currents to drive turbines. This technology is commercially

untested, although prototyped on a small scale at several locations and shows potential as a

feasible method of low temperature solar generation. As such solar chimneys will be

investigated in this report.


27

4.1.2.1 Richard J

4.1.2.1 Overview

A Solar Chimney, as described by Schliach (24)(25)(26), consists of a large collection area or

a transparent material, usually glass, that inclines gently upward toward the central chimney.

The solar radiation heats the ground and the air under this roof causing the air to rise upwards.

As the air rises it follows the gentle incline of the collector roof toward the chimney at the

centre. This continual movement of air draws in fresh air from outside the collector. As air

flows through the inlet it drives a turbine at the base of the chimney generating electricity, as

shown in Figure 16.

Figure 16 - Basic design of a single vertical axis turbine solar chimney shown top down and side view and illustration

of air flow through the system

Collector

The collector uses the thermal energy from the sun to heat the air under its canopy, similar to

a greenhouse. The canopy consists of sheet glass or transparent plastic suspended horizontally

a few meters from ground (2-8m) with an increasing height toward the centre. A simple

schematic of the collector frame is shown in Figure 17. A typical collector is 50-70% efficient

at converting solar energy into usable thermal energy (24). The overall efficiency of the

collector is affected by the material used to construct the roof as well as the ground surface

under the collector. Double glazing will improve efficiency by reducing heat loss when

compared to transparent acrylic, however glass will cost significantly more, a crucial

consideration when considering the collector will span a very large area.


28

4.1.2.1 Richard J

Storage

The ground under the collector acts as a heat store, allowing the plant to produce electricity

even into the night. The type of ground storage in the collector will affect the efficiency of the

collector; materials like granite will have a slightly lower efficiency than limestone or

sandstone (27). Additional storage, such as water, can also be introduced to increase power

output at night and create a more uniform production over time (26).

Chimney

The chimney is the main thermal engine of the plant; the chimney houses a pressure

difference caused by the temperature variation and altitude variation between the chimney

inlet and outlet. The air flow speed through the chimney is proportional to temperature of air

at the inlet and the height of the chimney. For a large solar chimney a temperature variation

of 35⁰C can be expected over the height of the chimney, resulting in air flows of around

15m/s (24)(28). As discussed in section 4.1.2.2 Modelling the efficiency of the chimney is

relatively low (<3%) and is dependant on the height of the chimney and the ambient ground

temperature, where the lower the temperature the better, ideal for the cooler British climate.

Turbine

The turbines, wind turbines, convert energy of the air flow into electrical power, these

turbines act “as a cased pressure-staged wind turbogenerator”(24) where a static pressure

difference is used rather than staged velocity. This means rather than a high air flow velocity,

a large pressure difference is desirable for electrical production. For a high production many

turbines may be required, Schliach suggests either horizontally mounted turbines around the

circumference of the chimney inlet or vertically mounted turbines at the base of the chimney,

(29) shows there is little difference in output between these configurations. Using a vertical

mounting for the turbines presents the advantage of using only a single turbine or a cluster. A

horizontal mounting will require several turbines, the quantity is determined by the

circumference of the chimney and offers less flexibility in choice of turbines, as such a

vertical mounting is considered preferable.

4.1.2.2 Modelling

A comparison of existing models for solar chimneys was conducted by Koonsrisuk et al (30)

using Computational Fluid Dynamics (CFD) to validate the solar chimney models proposed

Figure 17 - Basic design of collector framework to support transparent roofing


29

4.1.2.2 Richard J

by several authors, Koonsrisuk concluded the most accurate models where those proposed by

Schliach et al (24) and Koonsrisuk and Chitsomboon (31). This paper will model the solar

chimney power plant system based on the model created by Schlaich et al (24) due to the

simplicity of the model and its ease of implementation.

In the simplest form, the power generated a solar chimney can be expressed as the product of

the power input and efficiencies of the three main systems of the solar chimney; the Collector,

the Chimney and the Turbines:

[7]

[8]

Where power input at the collector is equivalent to the product of the collector area and the

solar irradiance per unit area:

[9]

The function of the collector is to convert solar irradiance into a thermal flow that can drive

the turbines, the larger the area greater the energy collected and thus a larger thermal flow.

The efficiency of the collector can be described by balancing the thermal variables in the

collector (32)(24)(32) :

[10]

[11]

Combining equations [10] and [11] results in an overall efficiency expression for the collector

as shown in (24)(32) of:

[12]

Where β is the thermal losses of the system, valid only for small values of ΔT. The α value is

the product of the transmission coefficient of the roofing material and the absorption

coefficient of the surface under the collector. Using Kirchhoff‟s law for an object in thermal

equilibrium, we can use the emissivity of the ground surface to arrive at its absorbivity.

Typically for a glass collector and an absorbent surface, like sand, a collector efficiency of

60-70% can be expected, however efficiencies can reach 90% for highly absorbent ground

types and transmissive roof materials.


30

4.1.2.2 Richard J

The collector creates a thermal difference between both the ambient temperature and the

temperature with in the collector, usually in the order of 10 - 35K (28)(26)(24). This

difference in temperature and the height of the chimney, cause a pressure difference between

the air at the chimney base and that at its outlet, Δρ. There is also an air flow through the

chimney due to the thermal flow from the collector and induced convection current. The

efficiency of the chimney can be expressed by examining the potential energy (pressure

difference) and the kinetic energy (air flow) in the chimney (32)(24):

[13]

This means that the efficiency of the chimney is mainly influenced by its height and the

ambient temperature. The turbines are positioned at the base of the chimney and covert the

thermal air flow through the turbine into electrical energy. These are axial turbines and can be

considered as static pressure wind turbines (29).

Schlaich shows that the maximum electrical power obtainable is produced when 2/3rds

of the

pressure difference in the chimney is used by the turbines(24). Using this information and

combining the equations [12] and [13] produces a term for the overall efficiency of the plant

and thus using [8] an expression for the electrical generation capacity of a plant.

[14]

The efficiency of the generator can be taken as a static constant for the first approximation. In

(24) it is shown that the efficiency for a single vertical axis turbine mounted at the chimney

base has a maximum efficiency of 66%, however efficiency can be improved by introducing a

counter rotor turbine or Inlet Guide Vanes (IGV's). This shows in Figure 18, the maximum

efficiency can be improved to 79%, this however will depend on the updraft velocity which is

dependant on the collector. This simple, cheap optimisation guides the air flow from the

horizontal to the vertical direction and channels the flow over the turbines (29). These air flow

guides provide a means preventing the supports from influencing the fluid flow through the

inlet. A configuration such as this is cheaper than a counter rotor system whilst yielding a

greater efficiency.


31

4.1.2.2 | 4.1.2.3 Richard J

Figure 18 - Top (left) and side (right) view of inlet vane guides for vertically mounted turbines used to

inprove efficency of turbine and support chimney

From the equation in [14] there remain two unknowns: One, flow velocity at the collector

outlet and Two, the Temperature variation created by the collector at this point. These values

will be modelled as constants based on the recommended values given in (24)(25)(26) and

(32). This is simple model that does not account for frictional and turbulent losses within the

system or the external wind flow. Despite this it can be considered a reasonable

approximation to solar chimney power plant.

This model also does not consider nocturnal production of the solar chimney as observed in

(24)(26). The ground under the collector maintains heat into the night allowing production to

continue, however in this case the solar irradiance, G, is considered 0 and as such the model

yields no output.

4.1.2.3 Validation

In order to validate the accuracy of this model it is necessary to compare known values from

an existing solar chimney plant to the simulated values from the model. The Manzanares

prototype plant was built in Manzanares Spain in 1981/2 to test the design and theory behind

solar chimneys and has published results available. The specification of the Manzanares plant

(26) is shown in Table 12.

Manzanares Solar Chimney

Chimney Height (m) 194.6

Chimney Radius (m) 5.08

Mean Collector Height (m) 1.85

Mean Collector Radius (m) 122

Nominal Power Output (kW) 50

Mean Temperature Difference (K) 20

Table 12 - Manzanares solar chimney prototype plant specification and observed environmental values

The prototype was built in order to practically test the possible generation capacities of the

plant for different conditions and the effects of different building materials on the plant. As

such the collector consisted of a mix of thin plastic film and glass over a sandy terrain with


32

4.1.2.3 Richard J

some vegetation. Using the transmission and absorption coefficients in Table 13, accounting

for discolouration and reduced transmission in the plastic film it is calculated that the

approximate α value for the Manzanares chimney collector is 0.56. From the recorded air

flow speeds at the Manzanares plant the turbine efficiency was estimated at 50%(9)(12).

Using the figures in Table 12 and the model described in 4.1.2.2 Modelling, a simulation was

created and compared against the observed results from the plant. This can be seen in Figure

19. It is noted that for these figures the nocturnal electrical production, G < 0, was not

recorded although an updraft was observed.

Figure 19 - Comparison of observed power output from Manzanares solar chimney prototype to simulated

results for Manzanares prototype

As shown above the simulation of the Manzaners prototype is reasonable accurate and

follows the trend of the observed results. The total percentage error for daily production is

3.26%; this is a low error and means the model can be considered a good approximation for a

solar chimney for daylight hours. The small error incurred is mainly due to approximation in

values for the solar collector transmission coefficient (α) and turbine efficiency (ηturb) as the

other parameters are given in (24) and (26). Through varying the parameters of α and ηturb it

will be possible to observe how robust/sensitive the model is to varying parameters, Figure 20

shows the percentage error of the simulation compared to the original for varying values of α

and ηturb. The variations in these values were investigated as they were not explicitly stated

and required a certain amount of judgement to approximate.


33

4.1.2.4 Richard J

Figure 20 - Variation in model error over a range of transmission coefficients and turbine efficiency to show

sensitivity of model

From this graph it is clear that the accuracy of the model is sensitive to small variations in the

base parameters of the collector. As such will be necessary to accurately predict such values

to achieve a reliable simulation, else large errors in results could occur.

4.1.2.4 Analysis

As shown in section 4.1.2.2 Modelling, the overall efficiency of the solar chimney plant is

mainly dependant on four factors; the chimney height, the collector radius, the turbine

efficiency and the material properties of the collector (α). As discussed the efficiency of the

turbine is assumed constant and with the use of IVG‟s can be taken at an value and

approximate value between 65-79% depending on the collector size and efficiency.

The efficiency of the chimney is proportional to its height, as shown in equation [13] and

[14], meaning that the plant overall efficiency will be heavily influenced by the chimney

height. A 50m chimney will have an efficiency of only ~2.5% and a 200m chimney an

efficiency of ~12% when considering a temperature variation of 20°C. This suggests that

solar chimneys are only viable when built on a large scale, requiring a large initial investment

in order to construct a large size chimney. The cost of the chimney is not linearly proportional

to its height, as such a compromise will have to be made to find the optimal height of the

chimney whilst minimising cost.

The collector efficiency is mostly dependant on the roofing material and ground surface. A

high transmittance in the roofing material and high absorbance of the ground surface will

result in a more efficient collector, the absorbance values of various surfaces and


34

4.1.2.4 Richard J

transmittance of different roofing materials can be seen in Table 13. These are approximations

as values will vary on the surface of the material and moisture content of the ground surface.

Material Absorption

Coefficient

Soil 0.38

Sand 0.9

Vegetation (grass) 0.96

Gravel 0.28

Chalk 0.9

Concrete 0.94

Material Transmission

Coefficient

Lifespan

(years)

Cost

(£/m2)

Glass 0.9-0.96 50+ ~21

Polycarbonate 0.86 20 ~4

Polyethylene 0.8 15 ~8

Acrylic 0.8-0.9 10 ~5

Table 13 - Material properties for solar collector roofing and ground surface type

The choice of roofing material used will have a large impact on the feasibility of the solar

chimney as a method of generation. Due to the large area covered by the collector a low cost

material is required, however the material must also be durable to last the life span of the

chimney (>40 years (24)) and have a high transmission coefficient to maximise efficiency. A

higher efficiency collector can be smaller than a low efficiency collector to achieve the same

power output, and as such is a major design consideration. Using values from the Table 13,

glass would provide the best efficiency as a roofing material due to its high transmittance.

Although when considering the cost it would be cheaper to use a translucent polycarbonate

and a slightly larger collector area and replace the roof every 20 years. In (24) it was observed

that the collector was relatively resilient to dirt and dust, although the roofing may soil

slightly it will have little effect on production. It was also noted that the occasional rainfall

was also sufficient to clean the collector suggesting that regular cleaning will not be required,

therefore reducing maintenance costs.

The type of surface under the collector will be highly dependent on the geographical location

of the plant, however will greatly affect the collector efficiency. Sand, with its high

absorbivity, is a good choice of material for the ground surface; however in the South East of

England this is not probable; creating an artificial surface under the collector, such as

concrete, is not feasible due to the cost of covering a large area. In order to create a high

efficiency collector growing grass or plant matter is recommended. Shown in Table 13

vegetation has a high absorbivity and can easily thrive under the collector due the greenhouse

like conditions as shown in (24). This can improve the efficiency of the collector by up to

~55% compared to an exposed soil surface. A significant improvement for a fairly low cost

modification. This also suggests the use of the area under the collector for agriculture, acting

as a large scale greenhouse, the collector could be used to generate extra revenue and improve

plant efficiency in comparison to exposed soil.


35

4.1.2.4 | 4.1.2.5 Richard J

The design life of a solar chimney plant is determined mainly by the chimney and is

suggested at up to 75 years depending on the climate (24). For this report the lifespan of the

solar plant will be taken at 40 years although a range of life spans will be considered. This

figure was chosen as a safe estimate based on the maximum lifespan of a steel-concrete

chimney in the British climate. It is expected that the collector roofing and turbines will

require maintaining and replacing during this period and will be considered when analysing

the feasibility of this form of generation.

In order to supply the village of 2,000 during nocturnal hours (or hours of non-production) it

is necessary to use short term storage. This will store a proportion of electricity generated and

redistribute it as required when the plant is not generating electricity. There are many forms of

energy storage however due to the nature of the solar chimney electrical storage such as

batteries or super capacitors are most feasible, discussed in section 4.2.1 Short Term Storage.

The required capacity of this storage must be large enough to meet the electrical demand of

the village during the interval between daily production cycles. In summer it is estimated that

demand for a village of 2000, during hours of darkness, is ~1400kW, where as in winter

nocturnal demand is much greater at ~4500kW (based on season definitions in section 3.3

Energy ).

The Solar chimney plant can require large amounts of reasonable flat land, 1-2km2demeding

on the power output required. As such the available topography will determine the feasibility.

Discussed in section 3.1 Geographical constraints there is limited available larger areas of flat

in the South East; however as mention above the solar chimney collector can be used for

agriculture. This suggests the plant could be feasibly built on flat agricultural land that could

be still be used for farming.

Another consideration with solar chimneys and their size is that the approval of local

residential communities. Due to the height of the chimney it would not be feasible attempt to

hide or disguise the chimney. Instead it is suggested winning the approval of residents could

be achieved by providing a viewing platforms at the chimney top and year round covered

community spaces in the collector such as parks and play areas. This should improve

resident‟s opinion of the plant without significantly affecting performance or cost.

4.1.2.5 Outputs

To provide a proport or all of the power for a village of 2,000, using a solar chimney, three

scenarios will considered A, B and C. These scenarios are based on the variation in solar

irradiance over the course of the year as shown in Figure 3. (A) The annual output of the plant


36

4.1.2.5 Richard J

will match the annual requirements of the village where seasonal storage will be used to store

the excess power from the summer and fill the short fall from winter production. (B) The

solar chimney plant will produce enough electricity to meet the demands of the village in

winter without the need for seasonal storage; excess power produced during the summer will

be sold to external buyers. (C) The plant will produce enough power to meet the total needs of

the village in the summer and will supplement an external power supply during the winter.

Each scenario will use the average demand of a village of 2000 shown in section 3.3 Energy

with the assumption that daily demand is constant, the solar irradiance values used will be

those of Portsmouth as southern location would be more desirable. Based on these figures the

estimated average hourly demand for each scenario in the given demand period are shown in

Table 14; the expected annual production and demand for each scenario are shown in Figure

21.

Scenario A will require both long and short term storage, B only short term storage and C will

require no storage at all. This will have a large effect the overall cost of the plant, as discussed

in section 4.2.1. Long term storage can be very expensive; as such the levelised cost for A is

high. Short term storage can be achieved cheaply and effectively using lead-acid batteries

which will be replaced every 5 years. The capacity of the storage will be required to meet

nocturnal demands all year round and as such will be have a capacity of 4500kWh in order to

meet winter demand.

For all scenarios it is assumed the plant will have a lifespan of 40 years with the collector

roofing replacement after 20 years, no nocturnal generation, turbine efficiency of 70% and a

solar irradiation trend as described in section 3.1 Geographical. The average hourly

production exceeds demand by approximately 5% for each scenario. This is to create a small

buffer for small variations in demand. Assuming the collector has a vegetative ground surface

and a polycarbonate roofing, the efficiency is calculated at ~0.73% with a cost per square of

9.22 £/m2 based on the design shown in Figure 17 (see Appendix 10.1.2 for a detailed cost

breakdown). The levelised cost is real terms cost of each kWh of electricity produced over the

lifespan of the plant based on the capital expenditure and operational and maintenance costs,

it is used to determine the most cost effective generation scenario.

Each plant is allocated 3 permanent staff members to perform inspections, maintenance and

monitoring, this does not cover staffing to perform power distribution to the village and

administration and logistics. Bi-weekly inspections of the collector roofing will be carried out

by contracted 6 staff that will be responsible for checking for and replacing broken roofing


37

4.1.2.5 Richard J

panels. Roofing panels are polycarbonate and as such resilient to breakage, however a 0.5%

replacement rate for the roofing panels has been assumed.

Scenario A B C

Av Hourly Demand (kW/h) 362 443 312

Av Hourly Production (kW/h) 380 465 328

Chimney Height (m) 200 360 150

Collector Radius (m) 640 845 500

Peak Output (MW) 2.1 6.5 1

Annual Output (GWh) 3.83 12.04 1.75

Short Term Storage (kWh) 4500 4500 1400

Seasonal Storage (MWh) 900 None None

Initial Capital Cost (£Mil) 166.05 33.78 12.5

Average OM (£Thousand/y) 571 428.8 286.5

Levelised Cost (pence/kWh) 117.7 10.6 28.1

Table 14 - Comparison of Solar Chimney Plant Outputs and Costs if constructed in Portsmouth to find most

feasible for a village of 2000

Figure 21 - Graph to show power production over the course of a year for a plant situated near

Portsmouth against annual demand for a village of 2000 for scenarios A, B and C

Based on these values the most feasible use of solar chimney generation is scenario B due to

its low levelised cost of 10.6p/kWh. Scenario B is the only scenario where the levelised cost

is lower than that of the average domestic electricity price, 13p/kWh as shown in Figure 7.

This means that in scenario B electricity can be competitively sold to consumers for profit and


38

4.1.2.5 Richard J

to external sources at a competitive rate. This suggests that profit per kilowatt hour sold to

consumers can be achieved, assuming sales in 2011 following the trends shown in Figure 7.

These values are based on the assumption that the solar irradiance will be the same as the

average for previous years. The production values shown in Figure 21 are based on irradiance

values for an area in the vicinity of Portsmouth, one of the most southerly areas of the South

East. These values are among the highest for the South East and will not be the same for more

northerly locations where the irradiance can be up to 7.5% lower, for example in the northerly

area of the south east, Bedford. The value of solar irradiance over future years will also not be

constant: if there is lower than average solar irradiance it will affect the amount of power

generated and thus the levelised cost. The average annual solar irradiance data for the South

East, UK as discussed in section 3.1.4 Solar Irradiance was varied by ±20% in order to

observe the effects on generation and levelised cost, as shown in Figure 22.

Figure 22 - Effect of variation in solar irradiance on levelised cost and annual electrical

production for scenario A, B and C

This shows the sensitivity of the plant to a variation in solar irradiance. The larger the plant,

the more sensitive annual production is to variation in irradiance. The larger the production

volume the less the cost of production will be affected by small variation. It also shows that

for an area with higher solar irradiance a greater production can be achieved, or alternatively a

smaller plant required to achieve the same production. As such it would be beneficial and

cheaper to place the solar chimney as far south as possible in order to reduce costs and

maximise production.

By generating an excess of power initially, the plant will have a buffer between generation

and demand, this will allow for small increases in demand to be absorbed with any excess

energy production being sold to external outlets (national grid, other settlements or other


39

4.1.2.5 Richard J

power companies). In Scenario B this 5% buffer is sufficient to meet the high demand case

until 2028 or the average demand up to 2050. If by 2028 the buffer is depleted, then the

collector can be easily enlarged to meet the higher demand, this will increase the levelised

cost however. It is recommend evaluating the energy demands from the village in 2029 as the

collector roofing would require replacing in 2030, based on 2010 construction, as which point

the collector can be enlarged or reduced based on demand.

It is assumed the excess energy produced by the chimney can be sold else where, however

this will be at a lower rate compared to selling to residents directly and as such is not so

desirable. Ideally to maximise profits, it would be best if the plant met the needs of the village

exactly in winter and the summer surplus be sold off, this would eliminate the need for long

term storage and ensure the majority of the generated power was being sold at maximum

price allowing. This suggests scenario B is more favourable compared to A which would

require costly seasonal storage and C which has a reduced output and large capital cost.

It is possible to increase the profitability of the chimney plant by using the area under the

collector to create extra revenue. The large covered area makes an ideal greenhouse and can

be rented for use in agriculture, this could be done at little cost and only a minor impact of

efficiency. A commercial greenhouse letting would require a small staff and a water

circulation system which could be achieved by collecting and re-distributing rain water on the

collector. An estimation of the itemised cost and design is shown in Appendix 10.1.4. Only

half the available area would be used each year as it would be necessary to rotate the used

land each year to preserve soil fertility.

Another method of raising revenue using the collector would be to create a covered year

round sports facility, by creating low maintenance facilities such as tennis and badminton

courts, bowling greens or potentially football pitches it is possible to create profit from the

collector without significantly affecting efficiency, Appendix 10.1.3, shows the itemised

sports facilities along with the associated financial data. The overall effects of these measures

in terms of profitability without inflation or tax over a 40 year period are shown in Figure 23.

Basic layouts of how these facilities could be incorporated into the collector are shown in

Figure 24. The remaining unused area at the edge of the collector could be used for public

spaces such as parks, grazing land, agriculture or as wildlife habits to appease environmental

concerns.


40

4.1.2.5 Richard J

Figure 23 - Cumulative profit before inflation and tax for hot house renting and sports facility busininess constructed in

the solar chimney collector

Unused area due to possible high

temperatures

Used as agricultural land, central area

used to good greenhouse conditions.

Land plots rented in a greenhouse

letting business

Houses sports facilities, near edge of

collector to preserve prime green

house land for agriculture

Use as grazing land or community

spaces such as parks

Figure 24 - Possible distribution of collector land space for use with business

The area of the collector available for use with agriculture will be less than the total area of

the collector, the inner area around the chimney inlet will have the highest temperature rise

due to the cumulative flow of hot air passing through that region; as such it vegetation may

overheat on hot days and will be left free from use.

As shown above agricultural use is most profitable, assuming the all plots can be rented, and

will heavily subsidise the price of electricity. The sports facility scenario is much less

profitable; however the sports facility is also aimed at improving public opinion of the plant,

and as such is only required not to make a loss.

-400

-300

-200

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0

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200

300

400

500

-8

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0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40

Spo

rt P

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)

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icu

ltu

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rofi

t (£

Mill

ion

)

Year

Agriculture

Sports


41

4.1.2.6 Richard J

4.1.2.6 Recommendation

Based on the outputs discussed above it is recommended that scenario B in Table 14 would be

the design of choice for a solar chimney power plant. This plant will require only short term

storage for nocturnal power distribution which will have a capacity of 4,600kWh. The

location of such a plant within the South East is important; it is advised to locate the plant in

the more southerly area of the South East such as Portsmouth, where there is much higher

solar irradiance than northerly areas. A comparison of a plant located in Portsmouth compared

to Bedford with the same annual production is shown in Table 15.

Scenario Portsmouth Bedford

Average Solar Irradiance (W/m2h) 132.5 133.5

Chimney Height (m) 360 365

Collector Radius (m) 845 873

Peak Output (MW) 6.5 7

Annual Output (GWh) 12.04 12.04

Initial Capital Cost (£Mil) 33.78 35.63

Average OM (£Thousand/y) 739.9 773.9

Levelised Cost (pence/kWh) 10.6 11.11

Table 15 - Table comparing dimensions and costs for solar chimney plants producing same annual outputs

in Portsmouth and Bedford

As shown it is more feasible to build the plant further south as the increased solar irradiance

allows for smaller plants with the same output.

The profitability of a solar chimney plant located near Portsmouth not inflated and before tax,

can be seen in Figure 25. The plant is based on the assumption that each kWh is sold directly

to consumers at 13p/kWh and excess exported at 11.5p/kWh. The effect of using the collector

to create extra revenue as described in section 4.1.2.5 is also shown. The dip at year 20 is due

to the large cost of replacing the collector roofing and the turbine overhaul maintenance.


42

4.1.2.6 Richard J | 4.1.3 Ahmed D

Figure 25 - Cash flow before tax and in real terms for a solar chimney plant with and without additional revenue

sources such as hot house renting and sports facilities

The plant without any additional revenue doesn‟t break even until year 38, and at the end of

the project life time the plant will have made £5.75Mil, a relatively small profit considering

the lifetime and investment. With the additional sources of revenue however, the cumulative

profit of the plant increases to £15.13Mil a much better, yet still relatively small profit. The

annual gross margin is consistently

In order to consider the benefit of investment in a solar chimney plant, the Net Present Value

(NPV) was calculated. The NPV is the sum value of the after tax cumulative cash flow and

indicates the value of the investment over time. A positive NPV indicates an attractive

investment. A risk factor must be considered when calculating NPV, power plants can be

considered relatively safe investments as power will always be required and as such will have

a low discount rate. Due to the nature of the technology involved being new and

commercially untested the risk will be greater. Based on this higher risk the NVP for a solar

chimney power plant will be calculated with a discount rate of 10%.

4.1.3 Solar Towers

In solar tower systems, incident sunrays are tracked by large mirrored collectors (heliostats),

which concentrate the energy, flux, onto convective heat exchanger called solar receiver. This

energy is transferred to a thermal fluid through a heat exchanger. After the energy is collected

by the solar subsystem, the thermal energy transferred to water via a heat exchanger. This

generates stream which can power a stream turbine to generate electricity (33).

The heliostat is composed of a reflective surface, a supporting structure and mechanisms used

to orientate it to follow the sun‟s movement. The most used reflective surfaces today are glass

-50

-40

-30

-20

-10

0

10

20

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40

Cas

h F

low

(£M

illio

n)

Year

Power Plant With Additional Revenue

Power Plant Without Additional Revenue


43

4.1.3 | 4.1.3.1 Ahmed D

mirrors. The most common mechanism used to orientate heliostat is a two-axis tracking

system. In addition the solar receiver is made from materials with high absorptivity in order to

minimise losses. The receiver is the key element of the plant and serves as the interface

between the solar portion of the plant and the more conventional power block.

The receiver transfers the received heat to an operating fluid (water or molten salts), This

fluid then transmits that heat to other parts of the Solar Tower Power Plant (STPP), generally

to a water deposit via a heat exchanger. The heat is used to generate high temperature steam

and to produce electricity through the action of a steam turbine (Figure 26). Latest advances

and research are focused to increase the thermal storage. At present a storage system has been

designed for the 17MW Gemasolar Thermosolar Plant project to with a thermal storage

capacity of 15 hours using nitrate salt as a storage medium (34).

Figure 26- a diagram showing how STPP works

STPP‟s are a young technology with several 0.5–10 MW pilot plants in the early 1980s, and

the subsequent improvement of such key components such as heliostats and solar receivers.

Solar plants like PS10 have provided a portfolio of alternatives which have led to the first

scaled up plants for the period 2005–2010. Those small 10–15 MW projects, still not

optimised, already reveal a dramatic cost reduction over previous estimates and provide a path

for a realistic LEC milestone of $0.08/kWh by 2015 (33).

4.1.3.1 Solar tower model

It is necessary to calculate the power output that can be achieved using solar tower in the

South East of England. As such a mathematical model of a STPP has been formulated; this

model will allow for the variation of key parameters of the plant in order to observe the effect

on output, as such the feasibility of using STPP for a village of 2,000 can be evaluated. The

overall power of a STPP is given by the product of the power in and plant efficiency minus

the power requirements of heliostat tracking:


44

4.1.3.1 Ahmed D

[15]

Where the efficiency of the tower plant is given by the product of the individual systems,

namely the collector, receiver, carnot cycle, heat exchange and the turbines:

[16]

Some of the efficiencies being used are from literature while others are calculated. The

efficiencies from and simulation literature are (35)(36)(37):

Collector

Efficiency (ηC)

Receiver

Efficiency (ηR)

Heat Exchange

Efficiency (ηhe)

Turbine

Efficiency ( turb)

Tracking Power

Ptrack

0.92 0.92 0.8 0.36 100kWh/y/helio

Table 16 - Solar tower power plant efficiency values

The receiver efficiency is defined as the quotient of power gain flux and concentrated solar

radiation flux on the receiver and can be formulated as (33)

[17]

[18]

According to the second law of thermodynamics, the higher the operating temperature, the

better the efficiency of a heat engine (for example, the one in a STPP plant). The heat engine

operating temperature is directly dependent on the solar receiver, or absorber, outlet

temperature. Moreover, with solar concentration, the receiver absorber aperture area can be

reduced, minimizing infrared losses. Finally, concentration of solar radiation allows us to

develop a smaller absorber, which has a larger cost reduction potential.

Combining the equation gives:

[19]

The maximum theoretical optical efficiency (when Tabs>Tamb) is the effective absorptivity of

the receiver α. The higher the incident solar flux (CG), the better the optical efficiency. In

addition the higher the absorber temperature, the higher the radiative loss and, therefore,

optical efficiency is lower. The higher the effective emissivity, ε, the lower the optical

efficiency, therefore it will be necessary to plot a series of graph showing how the geometrical

concentration ratio affects the power output and from these graphs the optimum concentration

ratio will be chosen alongside the Tabs. Tabs is calculated using the formula below:


45

4.1.3.1 Ahmed D

[20]

The Carnot cycle efficiency is the ideal efficiency (for reversible processes) that increases

with temperature and sets the thermodynamic limit of the conversion efficiency.

The combined efficiency of both systems can easily be visualized by multiplying the optical

efficiency of the receiver and the Carnot cycle efficiency. The result would represent the ideal

conversion efficiency of the receiver.

[21]

It is necessary to calculate the area of heliostats needed to provide electricity for 2000 people.

This is calculated using the formula:

[22]

The average power consumption in a year for an individual in the UK is 1500 kWh for 2010,

as shown in section 3.3. Therefore the average energy in an hour per person is:

[23]

A 5% contingency will be added to this value to allow for future increase in demand,

Obviously power consumption will change therefore adding extra power to account for worst

cases. Therefore:

[24]

Subsequently calculating the average solar irradiance (G) in a year using irradiance data for

Hurn:

[25]

A rough estimate of area is given by a rearrangement of [15] where area equals the total

power required over the product irradiance available and plant efficiency:

[26]

Since each heliostat will have an area of 90 m2 therefore the number of heliostat needed is:

[27]

Since area is determined it possible to calculate the receiver and Carnot efficiencies is

calculated using the formula below:


46

4.1.3.1 Ahmed D

[28]

[29]

The total receiver is given by the total of the carnot and receiver area efficiencies and is

calculated at:

[30]

The receiver formula was slightly changed from the original formula, Tabs4 – Tamb4 was not

used because it was different from other resource books and in addition it was not yielding

correct results.

Absorber Area Absorptivity (α) Emissivity (ε) Boltzmann constant (σ)

20 0.95 0.95 5.67e-08

Table 17- constants used to calculate receiver efficiency

An area of 20 m was chosen because the absorber area has to be as small as possible because

having a large absober area will increase radiative losses to the environment thus resulting in

a decrease of the receiver efficiency. Making the absorber area to small will make it difficult

for the heliostats to reflect sunlight. The absorber area is dependent on the total area of

heliostat. Absorptivity and emissivity of 0.95 is the typical figures used in commercial

receivers (33). There are two design options for a solar receiver, external and cavity-type

receivers. Cavities are constrained angularly and subsequently used in north field (or south

field) layouts, due to this reason it will be appropriate to use a cavity receiver for this model

(33).

Since efficiency is calculated throughtout the year it is neccessary to ensure if the power

produced is sufficient enough to provide the energy demand of 2000 people. If not a new

heliostat area must be calculated using the calculated efficiencies. The yearly power output is

calculated using [15]:

[31]

This power output is below the demand of the village of 2000 people which is approximately

3.0GWh; therefore the area of heliostat will be recalculated. The overall annual efficiency

will be used to calculate the required heliostat area.


47

4.1.3.1 Ahmed D

[32]

Using this figure the heliostat area required is given by:

[33]

Given each heliostat has an area of 90m2 the total number of heliostats required is:

[34]

Using this value the new annual power output was calculated, using [16] at: 3.15GWh

June

Hourly

Irradiance

kJ/m2

Hourly

Average

irradiance

(Wh/m2)

Heliostat

Power

output (Wh)

Hourly

averagePower

output (Wh)

Tabs(° C) ηR (%)

10:00 1876.07 521.13 10162445 2.53E+06 1730.2 95

11:00 2162.97 600.82 11716550 2.91E+06 1792.9 95

12:00 2388.10 663.36 12936073 3.22E+06 1837.8 95

13:00 2409.27 669.24 13050730 3.25E+06 1841.9 95

14:00 2298.97 638.60 12453247 3.10E+06 1820.4 95

15:00 2096.60 582.39 11357049 2.82E+06 1778.9 95

16:00 1774.03 492.79 10162445 2.53E+06 1706.2 95

Table 18 - hourly power output in June

It is important to distribute the heliostats evenly to reduce the shadowing effect; therefore a

spacing of 15 m will be used to reduce the effect. Therefore total land required is:

[35]

Also the heliostats will be situated north of the tower, since North fields improve performance

as latitude increases (33).

Figure 27 – common heliostat layout for optimising spacing and avoiding overshadowing (38)


48

4.1.3.2 | 4.1.3.3 Ahmed D

The height of the tower is determined by the distance of the last row of heliostats. The tower

is required to be tall enough for the last rows of heliostats to reflect sunlight to the receiver

which is located at the top of the tower. Therefore a height of 60 m will be chosen for this

area. This decision was made from reading case studies from existing solar projects (39)(40).

When the area the total area of heliostat is determined, the hourly power output that can be

produced with this area for January and June will be plotted. As well as the seasonal daily

average power output throughout the year will be plotted. This is done to determine how

much of the energy demand the STPP generate without the need for additional energy

sources.

4.1.3.2 Parameters

It will be necessary to evaluate different fluids and determine the most economical and

efficient fluid for use the working fluid. There are two main fluids used in industry these are:

Molten nitrate salt

Water/steam

The molten nitrate salt is an excellent thermal storage medium, however it can be a difficult

fluid to deal with because of its relatively high freezing point (220°C/428ºF) (41). To keep the

salt molten, a fairly complex heat trace system must be employed. Heat tracing is composed

of electric wires attached to the outside surface of pipes. Pipes are kept warm by way of

resistance heating. At present molten nitrate salts are not used commercially on a significant

scale however plants with this type of fluid medium are nearing the completion e.g. (Crescent

Dunes Solar Energy Project, Gemasolar Thermosolar Plant and Rice Solar Energy Project).

This will generate electrical output up to 15 hours without any solar feed(34).

When using water/steam as a transfer fluid direct generation of steam is undertaken without

the need for a heat exchanger. The steam produced by the solar field in the receiver, this is

used to operate a conventional power cycle, the efficiencies are good but the electrical

generation without solar feed is really poor only about 1 hour.

4.1.3.3 Results

The design dimensions required to create solar tower power plant capable of supply a village

of 2,000 are shown below. The plant described in Table 19 annually produces enough power

to meet the annual demand, however some form of storage will be required to distribute this

over the course of the year.


49

4.1.3.3 Ahmed D

Life

span

(years)

Nominal

power

(kwh)

Operation

(hr)

Short

term

storage

capacity

(hr)

Annual

efficiency

(%)

Area

covered

(ha)

25 year

power

output

(GWh)

30 year

power

output

(GWh)

25-30 3.25e6 22-13 1hr 14 29 78 94

Table 19 – Solar Tower power plant capable of meeting the needs of a village of 2,000 with additional

storage required

The working fluid used to transfer energy around the solar tower system will have a

significant effect on the efficiency and cost of the overall plant. The use of moltern salt and

water are considered where the average hourly outputs for a range of scenarios are shown in

Figure 28 and Figure 29.

Figure 28 - Power output for different scenarios using water as a working fluid

Figure 29 - Hourly power output for different scenarios using molten nitrate salt as a working fluid

It can be clearly seen that using molten salt as transfer fluid increases the power output as

well as the amount of heat that can be stored but it comes with a cost. Using molten salt

increases the power output by 6.5%, if the cost of using molten salt as a transfer fluid

increases the total cost of the plant by more than 6.5% then it is not worth using it. Since the

levilised cost of STPP is not as competitive as PV it will not be necessary to determine the

cost of using molten salt. Also from literature using molten nitrate salt increases the operating

3.25E+06

0.000E+00

5.000E+05

1.000E+06

1.500E+06

2.000E+06

2.500E+06

3.000E+06

3.500E+06

4.000E+06

00:0

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Hourly power output JuneHourly power output December

June worst case

June good case

December good caseDecember worst case

3.73E+06

0.000E+00

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2.000E+06

3.000E+06

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Hourly power output JuneHourly power output DecemberJune worst case

June good case

December good caseDecember worst case


50

4.1.3.3 | 4.1.3.4 Ahmed D

cost of the plant. Therefore I will use steam as the transfer fluid but molten salt as a storage

fluid.

Figure 30 – Annual power output from the STPP and electricity demand for 2000 people

There are 6 months in which the solar plant is producing below demand; this issue can be

solved by using seasonal storage. Since there are 6 months that electricity is being produced

above demand, this surplus of electricity can be stored seasonally. The total amount of

electricity which is surplus is = 982 MW, the amount below demand = 1699MW

The amount of storage capacity required = 1699-982 = 717 MW = 0.7 GW. This amount of

storage is far too much to be economically feasible. This amount of storage can be reduced by

increasing the size of the plant to meet the demand throughout the year. However this will

come at a cost.

4.1.3.4 Validation of result

It is important to compare the results obtained with real data in order to verify the accuracy of

the results obtained. Obviously there will be a degree of error associated with the calculation

and the results obtained but determining the amount of error will indicate the reliability of the

results.

Table 20 - annual and peak projected efficiencies of STPP based on various system configurations(33)

7.48E+07

4.99E+08

6.23E+07

3.30E+08

3.30E+08

0.00E+00

1.00E+08

2.00E+08

3.00E+08

4.00E+08

5.00E+08

6.00E+08

Jan Feb March April May June July Aug Sept Oct Nov Dec

Po

we

r o

ut

pu

t W

h/m

on

th

Month

Total monthly power outputMonthly demand


51

4.1.3.4 | 4.1.3.5 Ahmed D

The annual efficiency of the solar tower for this model is 14% which is within the minimum

projected efficiency as shown in Table 20. Also it would be important to compare the results

with real power output from existing plants but such data was difficult to find.

4.1.3.5 ChemCAD Simulation

In order to size pieces of equipment such as: the condenser, receiver and pump, it will be

necessary to simulate the process using ChemCAD simulation software. This will be the best,

most accurate way to determine the amount of steam required to generate electricity. Costing

on all equipment will be done based on the maximum power output achieved, this occurs in

June at 1.00 pm. ChemCAD will also give the loads on the heat exchanger and condenser as

well as the power of the pump.

From literature a 5 MW plant produces steam (40) at 440°C, 60 bar. The boiling point of

water at 60 bar is 275.5°C from steam tables. Cold water at 32°C, 0.05 bar is pumped to the

heat exchanger at a pressure of of 60 bar. This water is heated to 440 using sun energy to

generate steam. Two simulations were done, the first to model the amount of air required as

well as sizing the receiver. The second simulation, see Figure 26, was used to model amount

of water required to generate power in the turbine as well as determining the size of condenser

required. The power on the pump was determined in secomd simulation.

Figure 31- simulation to determine the size of heat exchangers and pump

Figure 32- to determine the amount of air required as well as the size of receiver

To maximize turbine generator efficiency, it is necessary to provide as great a temperature

differential as possible between the incoming steam and the exiting steam. Steam turbines

require a condenser to cool the steam after it leaves the turbine so that it condenses into water

and can be pumped back through the cycle. Instead of decreasing the temperature of the


52

4.1.3.5 | 4.1.3.6 | 4.1.3.7 Ahmed D

steam, latent heat of cooling is used. Phase change is allowed without decreasing the

temperature of the steam leaving the turbine. This makes the system more efficient and

energy is saved.

4.1.3.6 Cost analysis

Capital cost estimates for thermal power plants are often based on an estimate of the purchase

cost of the major equipment items. The other costs being estimated as factors of the

equipment cost. The accuracy of this type of estimate will depend on the reliability of the data

available on equipment costs. This method is used to give a quick rough estimate of the

capital cost. The list of component costings and variable values for various parts of the plant

are given in Appendix 10.3.1.

A summarisation of the key data points and calculated levelised cost is shown in Table 21.

The good case is when solar irradiance is increased by 15% and worst case is decreased by

15%.

Steam generation

Scenario Total irradiance

kWH/year

Levelised cost £/kWh

25 year life span

Levelised cost £/kWh

30 year life span

Good case 3.623E+06 £1.09 £0.91

Present data 3.15E+06 £1.26 £1.05

Worst case 2.68E+06 £1.48 £1.23

Table 21 - levelised cost for different scenarios

Fixed costs are defeined as (42):

Maintenance cost (Group, 2003) from table 5-20 = 15.3$/MWh

Therefore maintenance cost = 15.3*3150 = $48195/1.58 divide by exchange rate = £30503

Fixed Costs

1. Maintenance 5 -10 per cent of fixed capital £30,503

2. Operating labour from manning estimates £70,000

3. Supervision 20 per cent of item (2) £14,000

4. Plant overheads 50 per cent of item (2) £35,000

4.1.3.7 Financial analysis

A financial analysis of the solar tower power plant as described above, the cumulative profit of the £491,596


53

4.1.3.7 | 4.1.3.8 Ahmed D

plant is shown in Figure 33.

Figure 33 - Cumulative cash flow of solar tower investment

The profitability of a solar tower plant located at the South East not inflated and before tax, can be

seen in Figure 33 this is based on the assumption that each kWh is sold directly to consumers at

13p/kWh and excess exported at12.5p/kWh. The plant without any additional revenue doesn‟t break

even whatsoever. In order to consider the quality of the investment in a solar tower plant, the Net

Present Value (NPV) was calculated. The NPV indicates the value of the investment over time,

where a positive NPV indicates an attractive investment. A risk factor must be considered when

calculating NPV. A risk factor of 8 % was chosen due to the nature of the technology being

commercially unsuccessful; hence the risk will be higher, especially as is this is a small plant not

producing large amount of power.

4.1.3.8 Discussion

The levelised cost of solar power tower generation is dependent on demand and the amount of

solar irradiance available. It was necessary to correlate the significance irradiance will have

on the levelised cost; consequently irradiance was increased by 15 % to get best case and was

decreased by the same amount to get worst case. Last years irradiance data was substantially

greater than previous years therefore it was necessary to change irradiance and see the

significance this will have on the levelised cost. From Table 21 it can be seen that the good

case gives a levelised cost of 0.91 pence/kWh for a life span of 30 years compared to present

data of 1.05 pence/ kWh. The good case gives a 15% saving which is very significant.

Whereas the worst case gives an increase of 17% from present this is very costly.

-20000000

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0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30

Cu

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ativ

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ash

Flo

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£)

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Cumulative Cash Flow


54

4.1.3.8 Ahmed D | 4.1.4 Muhamed T

Solar tower power generation is not economically competitive enough to other solar

technologies for small scale energy production. This is because energy can not be produced

cost effectively because of the high maintenance costs of the plant due to the high

temperatures in which materials are exposed to and the frequent use of mechanical equipment.

In addition solar commercial power tower plants must be very large to take advantage of

economy of scales, to have more efficient designs, and to distribute the costs of the

maintenance crew over greater energy production. An independent study promoted by the

World Bank confirms STPP as the most economical technology to produce bulk electricity

from solar energy (Manuel Romero, 2002).

For the case of solar tower power plants, the degree of uncertainty on cost figures and

feasibility studies is relatively high since there is a lack of information concerning mass

production costs of solar components and O&M costs. Since the UK has good rainfall

throughout the year and snowfall during the winter, these environmental conditions will have

a significant affect on the performance of the cells. Solar processes are generally characterised

by high initial cost and low operating costs but for STPP the maintenance cost are relatively

high compared to other solar technology especially when producing energy in a small scale. If

this was a feasibility study to produce energy in a large scale STPP generation would be more

competitive. For all the reason mentioned above STPP generation will not be used to provide

energy for a village of 2000 people.

4.1.4 Solar Troughs

The design of solar thermal energy collectors has moved forward over the past decade and has

become more economically feasible with the progression of design. Costs per kilowatt have

been reported at $0.08 - $0.1 (43). Solar troughs consist of large liner parabolic curved mirror

concentrators which are used to focus the sunlight on to receiver tubes. There are located

along the line in which the trough is focused. A Heat Transfer Fluid (HTF), such as synthetic

thermal oil is circulated in the tubes and the oil is heated by the concentrated sunlight. This

heated oil produces steam to drive a generator or conventional turbine which can either be

part of a gas turbine cycle and conventional steam cycle, or integrated into a combined steam.

California hosts nine commercial scale solar trough plants ranging from 14 to 80 MW each

and can provide 354 megawatts of electric (MWe) total capacity. These power plants have

been operating for 27 years and have produced the largest solar thermal generating capacity in

the world (43).


55

4.1.4.1 | 4.1.4.2 Muhamed T

Figure 34 - Ariel view of the solar power stations SEGS III to VII (Solar Electric Generating Systems), KJC, Kramer Junction, California, with an installed capacity of 30MW each Invalid source specified.

4.1.4.1 Typical model of Solar Trough

Figure 35 is a schematic diagram of the process flow which represents the majority of

parabolic trough solar power plants available today. The heat receiver will heat up the fluid

that has been pumped into the receiver. After the heat absorption process, the fluid will be

transferred to the thermal storage at high temperature. Subsequently, the fluid is pumped into

the heat exchanger where the conventional power plant generates the steam that is necessary

to drive the turbines and generate electricity.

Figure 35 - The solar thermal power system

4.1.4.2 Parabolic Collector Structure

Figure 36 shows the solar collector and the absorber pipe which runs along the collector. Each

solar collector is built up from parabolic reflectors (mirrors), receiver tubes, the steel structure

and tracking system that consists of the sensors, driver and controls. This structure allows the

solar collector to operate at 150-400°C. The collector orientation is programmed to track the

sun from east to west during the day to ensure that the mirrors reflect sunlight for the longest

period possible, optimising power production.


56

4.1.4.2 | 4.1.4.3 Muhamed T

Figure 36 - Typical solar field of parabolic trough solar collector (44)

4.1.4.3 Heat Collecting Elements (HCE)

Figure 37 - Absorber tube (44)

Parabolic trough absorber tube is also known as the heat collection element (HCE) and is

shown in Figure 37. The HCE is the most important part of a solar trough because it will

determine the efficiency of the heat transfer. This structure is illustrated in Figure 28. The

HCE combines glass to metal seals and metal bellows for a vacuum-tight enclosure which

protects the surface as well as minimising heat losses. The optimised heat transfer efficiency

to the HTF from the solar radiation is provided by a ceramic compact heat

resistant alloy formed metal coating on the steel tube. Metallic substances are able to absorb

gas molecules and are introduced into the vacuum space to absorb hydrogen and other gases

that leak into the vacuum ring.

Figure 38 - Sample of 2-D view Invalid source specified. and 3-D view heat absorber element


57

4.1.4.4 | 4.1.4.5 Muhamed T

4.1.4.4 Fluid systems

The heat transfer system is the combination of solar heat exchangers, a pump, piping and

valves. Whilst the HTF is heated, it flows through the heat receiver and undergoes the heat

exchange process in the power block which produces high pressure superheated steam. Then,

the superheated steam is channelled to a reheat steam turbine/generator. The steam from the

generator is condensed (the condenser is fed by the mechanical draft wet cooling towers) and

fed back to the heat exchangers and water pumps to transform it back into steam. Meanwhile,

the cooled HTF is pumped back to the solar field and re-circulated again in the absorber pipe.

It is important to choose the right HTF since the right type of HTF will determine the type of

thermal storage technologies that can be employed in the plant. Figure 39 shows several HTF

and their properties.

At a very high operating temperature (>200°C), water could produce high pressures inside the

receiver tubes and piping. Hence, thermal oil is commonly used as a HTF due to its ability to

operate at this high temperature range. Since high pressure steam requires stronger joints and

piping is can be more expensive due to the increase quality and cost of the pipes.

4.1.4.5 Heat Exchanger

Conduction and convection are the two fundamental processes involved in the heat transfer.

As water is heated, its molecules will gain and spread the kinetic energy through conduction

process. As this happens, more space is occupied by the hot molecules compared to the cold

molecules above them.

Figure 39 - Heat transfer fluids (HTF) and their properties (102)


58

4.1.4.6 | 4.1.4.7 Muhamed T

In the collector, the heat is transferred from the absorber plates to the fluid by conduction. The

fluid is channelled through the carrier pipes to the heat transfer chamber where the convection

process take place to transfer the heat.

4.1.4.6 Control and tracking system

A parabolic trough collector is a dynamic device as it rotates around the tracking axis to

follow the daily movement of the sun. The powerful hydraulic drive units are essential to

rotate the heavy collectors.

4.1.4.7 Storage

Figure 40 - Extended solar trough with Storage Invalid source specified.

A solar trough power plant has the ability to store heat during the day, use it to generate

power at night and even during bad weather. Figure 40 shows the parallel system that allows

the heat to be stored while the power plant is still in operation. Unlike an oil/steam heat

exchanger, oil will be channelled to the oil/salt heat exchanger. Figure 31, represents the heat

that will be transferred to the molten salt. At the same time, molten salt will be pumped from

the cold salt tank through the oil/salt heat exchanger into the hot salt tank where the molten

salt is kept.

During cloudy conditions, heat stored in the hot molten salt will replace the sunlight. At this

stage the hot molten salt will be pumped into the cold salt tank through the oil/salt heat

exchanger. Heat will be transferred to the oil in the exchanger and normal cycles of thermal

exchange process will take place in the rest of the system. With this system the solar thermal

power plant can continuously provide energy to the users. For example, AndaSol power plant

in Spain is a mix of 25,000 tons of potassium nitrate and sodium heated at 384° C (723° F.) to


59

4.1.4.8 | 4.1.4.9 Muhamed T

ensure the storage tanks supply additional power even when the sun goes down (45).

4.1.4.8 Modelling mathematical

The mathematical model in solar trough is used to calculate the output and describe the

representation of the real situation. All the calculations are based on literature review and

collected data. There are two basic scenarios:-

a) Average case: average solar irradiance, normal efficiency of the solar trough system and

average power usage. (For the data refer to geography and social sections)

b) Optimal case: the same scenario as the average case however a high efficiency is used.

4.1.4.9 Power requirement

The power output is calculated using the equation below for the South East

Power required every hour for a year in average

Individual Requirement =1,500.00 kWh/annum in 2010 (section 3.3)

Village size =2,000.00 people

Hours in a year =8,760.00 hours (365x24hrs)

Power Average of the year, Pout = (Individual requirement x Village size) / Hours in a year

Pout = 342.47kW ≈ 400.00 kW (for the worst case scenario)

Solar Irradiance as average for a year

Total Yearly Irradiance =1,154,924.72 W/h (source?)

Hours in a year =8,760.00 hours (365x24hrs)

Yearly Average, G =Total yearly Irradiance / Hours in a year

G = 131.84 W/m2

Plant Efficiency

The plant efficiency can be calculated by a combination of the equations and literature from

previous research on the topic. The efficiency is calculated in two ways, optimal efficiency

and average efficiency.


60

4.1.4.8 Muhamed T

Solar reflectance and optical efficiency

The calculation of solar reflectance and optical efficiency was based on typical optimal data

for mirror reflection, receiver spillage, glass envelope transmission losses and receiver

absorption losses.

Figure 41 - Collector efficiency for various absorber tube diameter Invalid source specified.

Figure 41 shows that as the collector efficiency increases the absorber tube inner diameter

decreases. There are higher internal convection coefficients in the feed water flow rate when

the absorber tube inner diameter decreases. Although a high beam radiation will increase the

overall efficiency. For this study, the best scenario is a 38mm inner diameter absorber tube

with 50% efficiency under 140W/m2 solar irradiation.

Thermal efficiency

Receiver thermal efficiencies represent the radiated and convected receiver losses. Other areas

that affect efficiency are piping, storage and oil-to-steam thermal losses. From Figure 42, the

average thermal efficiency for a temperature collector of 150°C is around 70%.

Figure 42 - Thermal Efficiency graph versus collector temperature above ambient (35)


61

4.1.4.10 Muhamed T

Turbine and generator efficiencies

The solar industry uses efficiencies of 36.7% for the steam turbine and 98.0% for the

electrical generator (36).

Auxiliary power loads and plant availability

Plant design studies and good engineering practice use ~1% auxiliary load for heat transfer

fluid pumping, ~5% for all remaining miscellaneous loads and have a plant availability at

97.1%. The overall auxiliary power loads and plant availability calculations (36) are:

[36]

4.1.4.10 Total efficiency of the systems

There are much total efficiency calculated in reports and studies driven by researchers in

SEGS, SunLab, Sargent (46) and Burns & Mcdonnel (36). Table 13 displays the efficiencies

from the reseach and the calculations made.

Project

SEGS

VI

SunLab

Forecast

Sargent

&

Lundy

Burns &

McDonnel Design

Solar reflectance and optical efficiency - - - 0.80 0.5

Typical optimal data for mirror reflection 0.533 0.598 0.57 0.92 -

Glass envelope transmission losses - - - 0.96 -

Receiver spillage /Receiver losses 0.729 0.852 0.81 0.95 -

Receiver absorption losses - - - 0.95 -

Thermal efficiency - - - 0.78 0.7

Typical losses - - - 0.86 -

Piping and storage losses 0.961 0.967 0.967 0.95 -

Oil-to-steam thermal losses - - - 0.95 -

Turbine and generator efficiencies - - - 0.36 0.35966

The efficiencies of the steam turbine - - - 0.37 0.37

Electrical generator NA 0.996 0.996 0.98 0.98

Auxiliary power loads and plant

availability 0.98 0.94 0.94 0.91 0.91

Total System Efficiency (%) 10.6% 17% 15.4% 20.31% 11.49%

Table 22 - The total system efficiency analysis from studies, SEGS VI project and the calculation

Figure 43 - Solar trough efficiency by demonstrated and projected (47)


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4.1.4.11 Muhamed T

Figure 42 shows the annual solar efficiency as between 10-15%, this is reasonable and

coincides with the findings of 11.49%. For the overall calculation findings, the efficiencies

are listed below:-

ηplant (optimal) 20.3% (36)

ηplant (average scenario) 11.4 %

4.1.4.11 Plant Area

The calculation on plan areas are shown below, the total power out of the plant is given by the

product of the power in and the efficiency of the plant.

[37]

Where the power input is given by the solar irradiance per unit area and the area of the plant

collector.

[38]

Using the efficiency values, and known values for power requirements and irradiance it is

possible to estimate a required collector area, as shown below:

[39]

From [39] the area of collector and total complex for the optimal and the average case has

been calculated at:

Area Collector Complex

Optimal (m2) 14,945.64 20,000.00

Average (m2) 26,405.26 32,000.00

Table 23 - Estimated area values for solar trough collector and comples

4.1.4.12 Storage in summer times

Figure 44, shows that the power output generated from the models and the hourly average

demands in Winter and Summer. It is clear that, the power generated during day light hours in

the Summer can support the energy demands after sun set. There is a need for short term

storage to fulfil these demands. The storage required to support this is approximately

11.7MW/day. Details of the storage is shown in chapter Error! Reference source not

ound..


63

4.1.4.13 Muhamed T

Figure 44 - Power (Wh) demands and generate from the model

4.1.4.13 Winter Demands and Supply.

In winter, supply did not meet demand, shown in Figure 44. The total demand in the winter

period is on average 42MW per day, but the power produced is ~4.5MW per day. A way to

solve this problem is through using a seasonal storage system that can store energy in summer

and cover the deficit in the winter. This will need to store between 11-14GW per year

however, the 14GW storage is not realistic. Therefore, the only solution is to increase the

solar collector area. Figure 45 represents using a collector area of 80,000m2. As a result, there

is no need for seasonal storage as the generation can produce enough power to meet demand

both summer and winter. The surplus power can then be sold to the National Grid.

Figure 45 - Daily average power output Wh/month with new change -increase the total area of solar

collector = 80,000m2

0.00E+00

5.00E+05

1.00E+06

1.50E+06

2.00E+06

2.50E+06

00:3

0

01:3

0

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Po

we

r (W

h)

Solar Time (hours)

Power Output (Summer)

Winter Demand

Summer Demand

Power Output (Winter)

0.00E+00

5.00E+05

1.00E+06

1.50E+06

2.00E+06

2.50E+06

Jan Feb March April May June July Aug Sept Oct Nov Dec

Po

we

r o

utp

ut

(Wh

)

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64

4.1.4.14 Muhamed T

4.1.4.14 Costing

In order to evaluate the financial feasibility of solar troughs as a method of generation a cost

analysis must be preformed and a levelised cost calculated.

4.1.4.14.1 Capital costs

There are five major capital cost components that are mirrors, concentrator structure, thermal

energy storage, receivers and power blocks. The calculations for the capital costs made from

the SunLab and Sargent & Lundy (46) research is shown in the table below:

Case Sun Lab Sargent&

Lundy Estimate TOTAL

Project SEGS VI Trough 150 Trough 150

Service lifespan

25-30years 25-30years 25 years

Solar Collection

System (£/m2)

159 103 124 114 3,021,957.73

Support Structure,

(£/m2)

43 34 36 35 933,750.98

Heat Collection

Elements, (£/unit) 540 405 431 418 24,077.68

Mirrors, (£/m2) 27 18 20 19 509,318.72

Power Block, (£/kWe) 336 187 172 180 1,013,775.67

Thermal

Storage,(£/kWe) NA 244 181 212 48,649,824.30

Total Plant Cost, (£) £54,152,705.08

Table 24 - Costing values for a solar trough power plant including capital and OM

This plant also has the following associated with it:

1. Area size = 26405.26m2

2. Number of Heat Collection Element (HCE) = 58 Unit (average 470 m2/unit)

3. Maximum Generator = 5.6kWh peak

4. Thermal storage capacity = 229MW

The total capital cost for the solar trough plant is predicted as £54,152,705.08.

4.1.4.14.2 Operation and Maintenance

Figure 46 represents the Operation & Maintenance (O&M) cost of the power generated over

the design life (46). The costs for 2011 for operation and maintenance are between $0.013 and

$0.018 (£0.0083 to £0.0115) per KWe. Therefore the total operation and maintenance cost is

£136,234.57 per year (in 2011). All costs refer to the replacement of mirrors, HCE

maintenance, steam turbines, water and process in the turbine, staffing, services contracts.


65

4.1.4.14 | 4.1.4.15 Muhamed T

Figure 46: Operation & Maintain ace (O&M) cost over the power generates (46)

4.1.4.14.3 Levelised cost energy

The levelised power cost is based on achieving the annual net efficiencies. For comparison,

the estimated levelised energy cost for the plant without thermal storage is included in Figure

47. The calculated levelised energy cost is £0.68

Figure 47 - Levelised energy cost (46)

4.1.4.15 Analysis

The analysis of performance of the solar systems is conducted in two steps. First, estimation

of the total energy needs of solar trough generation and the contribution of solar energy

equipment by calculating the solar fraction:

[40]

[41]


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4.1.4.15 | 4.1.4.16 Muhamed T

This value is too small, by considering the economical savings resulting from the use of solar

energy for each application. Achieved by comparing the average financial climate through

calculating the economical fraction:

[42]

[43]

[44]

This value is negative and as such this method of generation is not economical. From the

calculation, solar troughs are not economical due to their high cost to build and the reduced

solar irradiation that is required.

4.1.4.15.1 Cumulative cash flow

Figure 48 shows that by the end of the design life (25 years), the cash flow of this project is

still negative. This indicates it not to a profitable investment if power is sold at a competitive

rate. The capital cost of this project is so high that the initial investment will not be returned

within the design life of this project.

Figure 48 - Solar trough model cash flow

4.1.4.16 Output and conclusion

The overall system has advantages and disadvantages to commercialization in south east of

UK. As discussed it is good for solar troughs to have low cost maintenance (around

£136,000/year) however the construction cost is high as is land requirement.

Type Value (average case)

Normalised value (£/kWh) £0.68

Total of Lifespan 25 years

Capital cost (£/year) £54,152,705.08

-55000000

-54000000

-53000000

-52000000

-51000000

-50000000

-49000000

-48000000

-47000000

-46000000

-45000000

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

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mal

ativ

e C

ash

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Year


67

4.2 | 4.2.1 Kim T

Operation and Maintainace (O&M) (£/year) £136,234.57

Efficiency total (%) 11.4%

Collector area covered ( m2) 26,405.26m

2

4.2 Storage

Solar generation cannot be used to provide 100% of the energy demand for an area without

support from either an additional energy source or a storage system. This is because all solar

powered plants are unable to generate energy at night. Electricity demand sees a peak just after

the sun has set, so significant storage capacity is required should no alternative energy source be

used to meet demand during the night.

Clean natural energy such as solar energy provides a clean alternative to nuclear power and to

fossil fuels. It does not produce waste that damages the environment. However the equipment

used to convert the clean energy and store it into a more flexible form of energy produces

pollution that may disturb the activity or balance of human or animal life, for example noise

pollution and visual pollution.

Solar energy production is difficult to forecast due to the unpredictable nature of the variables

which affect it, such as cloud cover and temperature. These variables cause fluctuation which

must either be resolved by the output of conventional plants or using storage to buffer the

fluctuations.

The two main storage types, seasonal and short term storage have been considered separately.

Seasonal storage and short term storage will work to different demand variables and will need to

be designed to accommodate different capacities and rates of discharge. Due to this the most

suitable types of storage which can operate at the required rates of discharge and store the correct

energy capacity may be different for seasonal and short term storage.

4.2.1 Short Term Storage

Short term storage is mainly used for mobile systems and solar electric applications due to

because of the small capacities and low discharge rates. The different storage methods considered

include: flywheels, capacitors, batteries and super-conducting magnetic energy storage (SMES).

Flywheels have an efficiency of 85% and store energy in the form of kinetic energy. They store

energy by increasing the speed of a rotating drum and when the energy is required it is released

until the speed has reduced. Flywheels are mainly used for small scale because the materials used

to make them are very expensive. Flywheels would not be a suitable method of storage because

they produce a lot of noise. One option would be to place the storage far from the village to

Table 25 : Final value calculate


68 4.2.1 | 4.2.1.1 Kim T

minimize the noise population to the village; however this would have to consider factors such as

loss of energy through transmission, and transmission costs. The second constraint that makes

flywheels unfeasible is the undeveloped on a commercial scale for its use in electrical storage

because they were previously used in rotating machinery (48).

Capacitors and batteries have many similarities, one of which is the modular structure. It allows

the device to be more portable and used easily. However, instead of storing energy in chemical

form, capacitors store energy in an electrostatic field. The life span of a capacitor is 10 years

compared to flywheels which have at least 20 years. The efficiency is also slightly lower at 80%.

Despite having a high power density due to the internal resistance, capacitors were deemed to be

less suitable for this study because of their low energy density. The low density means that the

storage would require a larger module to store the required energy for the small village of 2000.

These properties make capacitors more suitable for short duration power boosts rather than a

powering a household for the whole night (49).

Batteries are attractive for a number of reasons. They absorb and release energy directly and so

are easier to operate. Due to their modular nature they are easy to handle and transport, and they

also have little effect on the environment (see section 6). The batteries do not require any

machinery to facilitate storage i.e. pumps and turbines. Battery efficiency ranges from 60% to

95% depending on the battery and the depth of discharge executed. They are the most commonly

used storage for solar electric applications (50). SMES is another storage method in which the

energy can be directly stored and discharged. The efficiency can be is as high as 90% but

unfortunately they are very expensive on a small scale. SMES can only become economically

attractive on a larger scale. Therefore batteries were deemed the most appropriate storage device

for electricity storage and will be explored in greater detail to assess their feasibility for this

project.

4.2.1.1 Batteries

The energy stored in batteries is chemical energy which is then converted directly into electrical

energy through electrochemical discharge reactions. In many cases batteries are needed to

regulate the fluctuations of power output. An analysis of different types of batteries was

conducted in order to select the most appropriate battery. These selected batteries would be

required to store energy from the PV plant and the solar chimney. These two competing

technologies were deemed the most feasible for the study and both store electrical energy. The

battery used for both generations is lead-acid because, the most frequently used batteries for PV-

systems are lead-acid and nickel-cadmium, hence the reason they were an interest from the

beginning (51). The purpose of this investigation is to analyse different battery performance and


69 4.2.1.2 Kim T

subsequent costs that would be incurred. The main units of the system to be aware of are: a

charger, the battery of choice, inverter and a cooling system or an air conditioner. Cooling

systems and air conditioners are required to keep the storage room cool and reduce the losses

from the components because of overheating. The inverter is a device that converts the power

from dc to ac. Six of the most common batteries were evaluated in order to identify the most

effective battery for the generating technologies and a comparison was completed to guide the

choice made (see section 4.2.1.6).

4.2.1.2 Goals and scope

The goal is to analyse some of the battery performance characteristics in order to show which is

the most viable battery i.e. assess the characteristics and measure the benefits of each to find the

most economically feasible solution with the most favourable performance. The batteries

evaluated were lead-acid, ni-metal-hydride, nickel-cadmium, lithium-ion, zinc-bromine and

sodium-sulphur. The variables are:

Energy requirements for the production and transportation of the batteries.

Charge-discharge efficiency, which is the efficiency for the battery to charge and

discharge the battery.

Service life, which is the life time of the battery after which it can no longer be used.

The investigation of production and transportation energy requirements is a large area of study.

This also includes the analysis of the transport distance to the site and energy required to power an

air conditioner. Transport contributes about 1 to 9% for road transport and 73% for air, and the

production of PV arrays and batteries ranges from 24% to 70% of the energy. This is an area that

requires more investigation when there is time; unfortunately this was a section that had to be

ignored because there was not enough time and space in the report (50).

Figure 49 shows the PV-battery system components and energy requirements, Eli. The image

shows production and transportation of a component. It also shows a PV array converting solar

energy into electrical energy which is either sent to an inverter to be immediately used or stored

by the battery. The energy is then distributed to users after it has been changed from dc to ac by

the inverter. Only the charger, battery, inverter and the AC are analysed for this storage study.


70 4.2.1.3 Kim T

Figure 49 - PV-battery system components and life cycle (51)

4.2.1.3 Description of the batteries

Table 26 shows a summary of the common batteries that have been studied and the some of the

characteristics used to determine the best battery; the efficiencies, operating temperatures, costs

and rated powers. Lead-acid and ni-cadmium are the most frequently used technology for

photovoltaic application. However lithium-ion and ni-metal-hydride are growing rapidly in the

small scale applications but their high production cost has limited their use for storage.

Battery Type Efficiency

range (%)

Operation

Temperature

Capital Costs

($/kWh)

Rated Power

(MW)

Lead acid (PbA) 70 to 84 -20 to 60 100-125 0.002 to 60

Ni-metal-hydride (NiMH)

65 to 85 0 to 40 525-540 0.01 to 2.5

Nickel-cadmium (NiCd) 65 to 85 -50 to 50 300-600 0.005 to 50

Lithium-ion (Li-ion) 85 to95 -20 to 50 600-1200 0.005 to 2

Sodium sulphur (NaS) 75 to 83 310 to 350 350-500 1 to 80

Zinc Bromine (ZnBr) 60 to 73 10 to 40 150-250 0.1 to 6

Table 26 - Description of the common batteries used (51),(52),(53),(54)

Deep cycle PbA is designed to store large amounts of energy, quickly during charging sessions. It

has heavy non-porous plates that help the battery to withstand repeated charge-discharging cycles

(55). The advantage is the low capital costs and the main disadvantage is cycle life which is

limited when discharged deeply. This means they have to be closely monitored so that they do not

completely discharge.


71 4.2.1.3 Kim T

Nickel alloy batteries, i.e. NiMH and NiCd, have high energy and power densities, require low

maintenance; however the capital costs are higher than PbA batteries and another disadvantage is

that they are difficult to dispose of at the end of their life.

Li-ion batteries have their anode and cathode made of carbon and lithiated metal oxide

respectively. Figure 50 shows Li-ion during charging. In the cathode, the lithium atoms become

lithium ions and flow through the electrolyte into the anode where they are deposited in the

carbon layers as atoms. The process is reversed during discharge. This battery is most commonly

used for vehicles and laptops because of the high energy densities. The capital costs are very high,

ranging from $600 to $1200/kWh(54).

Figure 50: Lithium ion battery

NaS batteries operate at high temperatures as shown in Table 26, thus the battery must not be

allowed to cool down otherwise the molten sulphur and sodium in the battery will solidify,

damaging the battery. This molten state provides sufficient electrolyte conductivity. The

electrolyte is a sodium ion conducting solid. The main issues with NaS are having backup power

available and safety issues concerning the design because of the high temperatures. This means

backup generator costs must be included in the total installation costs and safety precautions.

Exposure to moisture will cause corrosion and cause the sodium to combust, so for protection the

batteries are sealed.

ZnBr has liquid electrolytes which are pumped from electrolyte reservoirs into the battery stack

in two circuits where one is for the cathode half and the other half of the cell is the anode. ZnBr

batteries are not as expensive as the other batteries; the capital cost is about $150 to $250/kWh

(52).


72 4.2.1.4 Kim T

4.2.1.4 Method Used to Calculate Parameters

The following calculations were used for both the PV system and the solar chimney. The same

assumptions (see section 4.1.1.9 and 4.1.2.5) were made for both technologies. The only

difference is the site of the storage device which will later be discussed in further detail.

Assuming an average value for the battery efficiency (refer to Table 26), 92.5% for the charger

efficiency and 93% for the inverter. The output was calculated as follows:

[45]

a) Calculating the service life

The cycle life or the float life limits the battery service life. Assuming 365 cycles per year the

service life of the battery is calculated. The assumed temperature for the temperature factor is 30,

see Appendix 10.4.1 for service life factors, cycles and costs for the solar chimney battery

options. Using the average number of cycles, N, the cycle life is therefore defined as:

[46]

The float life is given by:

[47]

b) Calculating the Cost of the System

Costing has been considered for the following major components:

Inverter

Solar Technology (solar panels or solar chimney, see section 4.1.1.6 and 4.1.2.5)

Batteries

The cost of the charger has been ignored because the value is too small to make a difference to the

total costs. This section only includes methods for calculating the cost of an inverter, batteries,

and estimates for the AC and generators. The prices of the AC and the generator were taken from

consumer reports and rough estimated where made (56). The total costs are added up together to

give upfront costs and life-cycle cost per kW of solar energy (57). Most of the costs were obtained

in US Dollar and then converted into the pound using an exchange rate of 0.632098 (58).

i. Cost of Inverter

The costs are given as a function of peak power. Note for electrical applications the units for

power are usually in kilowatts (kW). The size of the inverter is defined by the amount of peak


73 4.2.1.4 Kim T

power that can be delivered. The peak usage for the whole year is 650kW for solar chimney

calculations and 820kW. So when scaled down to peak usage per house, it is 0.984kW. So

assuming

[48]

Assuming the cost for inverters is round about $1550/kW kW (59), the cost as a function of peak

power is:

[49]

Where the equation the becomes

[50]

ii. Cost of Batteries

Battery costs are calculated as a function of energy used. The energy stored by batteries is the

energy used after dark and on cloudy days. To maintain a long life, overdrawing and overcharging

the battery should be avoided. For instance if a battery is discharged at 50% per day it would last

at least twice as long, unlike a cycle of 80%. However a shorter discharge causes the costs to rise

because of the size of the battery. So assuming the discharge is 80%, the battery will store:

[51]

Using the battery costs in Table 26, total battery costs were calculated for best and worst cases.

The following equation was used:

[52]

iii. Total Annual Cost Calculations

This is just simply adding up all the costs:

[53]

iv. Operating Costs and Capital Costs for the life cycle of the plant

[54]

To calculate the capital cost for the life cycle, multiply the capital cost per year by the number of

times the component needs to be replaced.


74 4.2 1.5.1 | 4.2.1.5.2 Kim T

4.2.1.5 Battery Performance, parameters and Assumptions

4.2.1.5.1 Energy Efficiency

The energy efficiency is the ratio of the output energy and the input. For batteries the efficiency is

also known as charge-discharge efficiency because it takes into account one whole cycle.

Chargers have 90% to 95% efficiency, and inverters have 90% to 94% of efficiency. To calculate

the output energy for the charger and inverter, an average efficiency value was used. It is assumed

that temperature deviations are included in these efficiencies. Table 26 shows a range of

efficiencies for the batteries. Li-ion has the highest efficiency and ZnBr has the lowest.

Temperature is a factor that affects efficiency of a battery therefore the storage room temperature

has to be maintained at a constant level using a passive or an active system. Passive systems are

based on insulation and may also use water circulation systems to cool the room. They do not

need any electricity as an energy source to operate. Active systems such as the air conditioner

require energy to regulate the temperature. Thus, it is assumed that cooling is provided by the air

conditioner using the electricity converted by the panels. The AC provides enough cool air to

produce ice or cold water which keeps the temperature constant at all time (51).

A temperatures factor is also applied because if the temperatures go below the operating

conditions this may freeze electrolytes and high temperatures can damage the battery (49). This is

because the chemical activity increases to a point where the battery can no longer perform well

and the chemicals start to break down. So for example a temperature of above 40 degrees Celsius

would damage ZnBr but not cause any damage to Ni-Cd because it has a more robust mechanical

design (51). NaS operates at very high temperatures so safety precautions such as insulators are

required.

4.2.1.5.2 Service Life

Float life estimated the service life because of corrosion processes. The battery is usually deemed

to be the end of its service life when it is working at 80% of its initial capacity or when it stops

working entirely. Ambient temperature affects the performance and service life of ZnBr and NaS

batteries, so the effects are limited by regulating the operating temperatures with a thermal

management system or pumping the electrolytes. The batteries‟ service life will normally be

limited by float life or cycle life depending on which is reached first. A cycle is when a battery is

discharged and then charged back to its initial level. Deep cycle or depth of discharge (DOD) is

another way of describing state of charge (SOC). Thus the choice of battery defines the depth of

discharge (DOD) which limits the service life of the battery. To estimate SOC, subtract 100%

from DOD. When the battery is charge-discharged at 20%, this is referred to as a shallow

discharge. Deep cycle on the other hand have up to DOD of 50% to 80% and are charge-


75 4.2.1.5.3 | 4.2.1.5.4 | 4.2.1.6 Kim T

discharged repeatedly without getting damaged. Shallow cycle batteries are used for starting cars,

whilst deep cycle batteries are better for PV systems and solar chimneys (60).

4.2.1.5.3 Estimating the demand

Demand versus production curves were plotted so that the amount of power produced and power

required could be estimated (see section 3.3 for the demand for 2000 inhabitants). Figure 51 show

the production from the PV plant of electricity supply to one house. The electricity from the plant

was approximated to give electricity produced per household instead of electricity for 2000

inhabitants. However the costs of the small batteries for the PV plant will be scaled up to compare

with the storage for solar chimney.

Figure 51 - Shows the winter production of the PV plant and demand curves per household

It was assumed that for a solar chimney, the batteries would be situated on the same site as the

chimney. This means that the energy required for 2000 people or the 833 homes is stored in the

batteries and is then distributed to the residences straight from the plant.

4.2.1.5.4 Cost of the System

The battery costs were calculated for a best and worst case scenario. To calculate the cost of solar

electricity the upfront cost to install the technology and the life-cycle costs must be estimated. In

the calculations, only the major components were taken into consideration. The cost of the

charger was ignored because the price is so small it would make little difference in comparison to

the other components.

4.2.1.6 Storage Scenarios and Summary

The short term storage for the solar chimney was designed for worst case circumstances, which is

in December. In winter, the production levels are lower because there is not enough sun during

the day so the chimney cannot produce enough electricity. Secondly, the demand level is high due

0.00

250.00

500.00

750.00

1,000.00

1,250.00

1,500.00

1,750.00

2,000.00

2,250.00

2,500.00

01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23

Outp

ut (W

)

Time of day (hr)

Summer

Production

Summer

Demand


76 4.2.1.6 | 4.2.1.7 Kim T

to increased usage of heaters, lighting and water heating, thus the demand capacity is high (see

section 4.1.2.5). The demand capacity is defined in this case as the amount of energy that needs to

be provided after dark. In the summer, the battery storage levels are lower because there is more

sunlight combined with a lower demand. The battery designed for the solar chimney is for

scenario where the plant capacity is increased in order to store enough electricity to supply to the

village.

The capacity in winter was calculated to be 4.41MW. This was calculated by summing up the

demand when the solar chimney was not producing electricity. This is a rough estimation and

therefore a modified value of 4.5MW was made in order to account for the periods when the

electricity starts to decrease or the curve begins to level off on the graphs such as in Figure 51.

The calculated capacity in summer is 2.78MW. The battery is charged to full capacity each time

so when the battery is in use during winter the DOD is 80%. However, when the battery is in use

during summer, it is only being discharged partially. This increases the number of cycles. Thus

the number of cycles increases in summer. The depth of discharge is then reduced, thus

prolonging the service life of the battery. The battery is charged to full capacity each time but is

only discharged to at least 40%. So the actual lifespan of the battery will be the sum of the

service life at 80% and 40%, as shown in Appendix 10.4.

Alternatively, The PV battery storage is designed for summer because the panels do not produce

enough energy in winter. The panels only produce 2.3kW which is all used up, therefore there is

no energy stored. The demand capacity is 12.77kW which can either be supplied by the grid or;

the remaining energy from the summer production can be stored for winter. The option selected

was to buy electricity from the grid because the calculations involved are time consuming and the

space available in the report in minimal. The estimated capacity in summer is 5kW.This is to be

supplied over 10 hours thus as a result the battery charging time is 14 hours. The battery is

designed to store 9.44kWh of energy (see Table 29).

4.2.1.7 Solar Chimney Storage Results

Using goal seek in excel the input required for batteries to produce a capacity of 4.5MWh for

PbA, Ni-Cd and NaS was 8.49MW, 8.72MW, 8.28MW respectively. Appendix 10.4.3 and Table

28 show the quantity stored in the batteries and the annual battery costs. The most expensive

batteries are Ni-Cd and NaS. It is recommended that NaS should have a backup generator in case

of emergencies because it operates at high temperatures. Therefore, an estimated cost for a

generator was included only for NaS. A 10% contingency was applied because it is possible to

overlook factors. For the operating and maintenance costs (OM), operating labour and wages,


77 4.2.1.8 Kim T

which would normally be included, were omitted because these costs will be part of the plant

costing analysis (see section 4.1.2.5). This will make it easier to add the battery system costs to

the plant costs. The factor included in the OM was maintenance. Little maintenance is required so

2% was believed to be enough to cover for instance cleaning supplies.

4.2.1.8 PV Plant Storage Results

The evaluation method for the PV plant battery storage was similar to solar chimney. However, a

few differences were noted in the results;

The number of replacements alters because the life span of the plant is 40 years. The charger,

inverter and AC all need to be replaced at least three times. PbA, Ni-Cd and NaS need to be

replaced 16, 8 and 2 times respectively. Assuming that the number of cycles are the same, the life

cycle of the batteries is not affected because the same depth of discharge is assumed (refer to

Table 26).

The costs change because the scenarios are different however the costs are scaled up so that they

can be compared to the solar chimney battery costs.

Note that some of the assumptions are different for the storage, for instance a backup generator is

recommended in the homes in case emergency for the PV application. There the cost of

generators was included in all the battery costs.

The design specification of the battery was different, as mentioned above; the PV plant does not

produce enough electricity for winter so the battery was only designed for summer storage. The

battery is for a scenario where the plant is producing electricity only in summer because the

winter production is not enough to meet demand. The total amount of electricity being produced

in winter is 2.3 kW and the total demand required for one day is 12.77 kW per household. The

option is to supply electricty from a seasonal storage method or buy electricity from the grid.

However to simplify the anaylsis, it is assumed this additional electricity is provided from the

grid.

In summer, the electricity is generated from 0500 am to 1900 from the solar plant. The total

produced is 19.85 kW and the demand during this time is 5.88kW. The remaining energy is

therefore 13.97 kWh. After dark the amount of electricity that needs to be provided per household

over 10 hours is 5 kWh (The calculated capacity was 3.5kWh and 5kWh was estimated). Hence to

account for losses, 9.44 kWh has to be stored in the battery (see Table 27).

Different batteries have differrent discharge times; PbA, NiMH and NaS have a maximum

discharge time of 10 hours. Ni-Cd and Li-ion have a maximum discharge time of 11 and ZnBr has


78 4.2.1.8 Kim T

the lowest of 2 hours. It is important that the selected battery is capable of discharging over the

required time otherwise too many batteries would be required (61).

Table 27 shows the service life of PbA as 80% of DOD. Deep discharges drain the battery‟s cycle

life. This is especially a concern for PbA because deep discharges cause the structural of the

battery‟s active material to change and at the same time creates lead-sulphate crystals with low

conductivity. This sort of structure causes difficulties in recharging the battery back to its full

capacity so the battery should not exceed 80% depth of discharge (51). t3,cycle and t3,float are life

limiting conditions, and the one that is reached first determines the service life. t3,cycle is the

number of cycles divided by 365cycle/yr, and t3,float was already estimated by Rydh et al (2005).

The determination of this value requires capacity testing by fully discharging the battery at

different interval i.e. 20 days. The tables in the Appendix 10.4 shows that for 80% DOD Li-ion,

NaS and ZnBr have the highest cycle life and while Ni-Cd has the highest t3,float . NaS has the

highest service life and PbA has the lowest. This is big disadvantage because the battery has to be

replaced many times and this affects the cost of running the battery over the life span of the plant.

Table 27 and Table 28 show that PbA is the cheapest battery. Both the capital cost and the

operating costs are significantly lower than Ni-Cd and NaS. The AC for the storage room ranges

from about £189 to over £700 (56). The specifications of the AC were not available so it is

assumed the typical home system AC that can maintain cool temperatures is £284.

Fixed Capital

Cost (CFC) (£)

Quantity

Stored/Peak

usage

Unit Price

£ Unit

Total

Cost £

(BEST)

Price

£ Unit

Total

Cost £

(WORST)

PbA 9.44 kWh £ 63 £/kWh £ 595 £ 79 £/kWh £ 746

Ni-Cd 9.69 kWh £190 £/kWh £ 1,841 £ 379 £/kWh £ 3,673

NaS 9.20 kWh £ 221 £/kWh £ 2,033 £ 316 £/kWh £ 2,907

Backup

Generator 6 - 12 kW

£

1,300 - £ 1,300

£ 1,300

Air

conditioner

£ 284 - £ 284

£ 284

Inverter 0.984 /kW £ 981 /kWh £ 965 £ 981 /kWh £ 965

ANNUAL CAPITAL COST, inc 1% contingency

PbA

£ 3,175

£ 3,328

Ni-Cd £ 4,434 £ 6,284

NaS £ 4,628 £ 5,511

Table 27 - Annual capital costs for the PV plant battery options (62),(63),

The backup generator was included as a precaution, the chances of its constant use are minimal

and so it may not need to be replaced for a long period of time after it‟s installation. As a result it

can last, or be used over the 30 year life span without replacing it. The cost for a generator for


79 4.2.1.8 | 4.2.1.9 Kim T

systems that require 6 -12 kW power is $2100 or £1300 (56). The operating costs include 1% for

maintenance costs because minimal maintenance is required. The maintenance is mainly for the

backup generator which needs engine oil; carburettor air filters and fuel filter (56). A 5%

contingency was included in for items that were not included i.e. fuel for the generator.

Direct Costs Percentage Total Cost £

(BEST)

Total Cost £

(WORST)

Maintenance (MTC) 1 % of CFC b £ 6 £ 6

Replacement 80% of CFC

Lead Acid £ 476 £ 597

Nickel Cadmium £ 1,473 £ 2,938

Sodium Sulphur £ 1,627 £ 2,326

Total Direct Costs

Lead Acid £ 482 £ 603



TOTAL ANNUAL EXPENSES (CFP), inc 5%

contingency

Lead Acid £ 506 £ 633



Table 28 - Annual operating costs for the PV plant batteries options (64), (63)

4.2.1.9 The Complete Battery Design and Costs

After the results were analysed, PbA was found to be the most feasible battery for both solar

electric generations. The table below shows a summary of the two batteries. PbA is the most

feasible battery due to a number of factors. The cost of the battery is low and it has a high rated

power, however the downfall is that it has a lower discharge rate compared to other batteries.

Solar Chimney PV Plant

Winter (kW) Summer (kW) Winter (kW) Summer (kW)

Accessible energy 2,400 52,000 0 14

Capacity 4,500 2,780 12.77 5

Energy stored (kWh) 7860 Grid 9.44

Battery Capacity 7,860 kWh 9.44 kWh

Energy Output/Used,

winter 80%DOD (kWh) 4840 -

Energy Output/Used,

summer (kWh) 2989 5.39

Estimated DOD (%)

during

summer/Assumed DOD

38 80

Table 29: Summary for the solar chimney and PV plant PbA battery storage


80 4.2.1.9 Kim T

The table below is the cost of PbA per year and the costs for the whole lifespan of the plant. The

costs are only based on the worst case prices. The PV plant battery costs were also scaled up to

show how much it would be on a larger scale. This is shown Table 31.

Components Capital

Costs £/yr

O&M

Costs £/yr

Life Cycle

Capital Costs £

(worst)

Life Cycle

O&M Costs £

(worst)

PbA £ 620,940 £ 522,115 £ 4,967,520 £ 24,858,600

Inverter £ 637,650 £ 0 £ 2,550,600 £ 0

AC £ 284 £ 31.65 £ 1,420 £ 2,402

Total for 2000

people

£ 1,384,761 £ 548,254 £ 7,519,540 £ 24,861,002

£ 1,933,015 £ 32,380,542

Solar Chimney £33,780,000 £428,800 £33,780,000

£34,208,800

Chimney Storage

Modified £36,141,815

Table 30 - Summary table of PbA worst case annual costs and life cycle cost for the solar chimney

Components

Capital

Costs

£/yr

O&M

Costs £/yr

Life Cycle Capital

Costs £ (worst)

Life Cycle O&M

Costs £ (worst)

PbA £746 £ 597 £ 11,775 £ 28,401

Inverter £965 £ 0 £ 2,896 £ 0

AC £284 £ 31.65 £ 1,065 £ 1,802

Backup Generator £1,300 £ 6 £ 1,300 £ 180

Total for house £ 3,328 £ 665 £ 17,036 £ 30,382

£3,994 £ 47,418

Total for 2000

people

£

2,773,346 £554,976 £14,196,725 £25,318,429

£3,328,321 £39,515,154

Total(Cap+OM) £3328321 £39515154

PV Plant £2592657 £433150 £2592657 £12994504

Total(Cap+OM) £3025807 £15587161

PV Storage Modified

£6354128 £55102315

Table 31 - Summary table of annual costs of running lead acid and the life cycle cost for the PV system (worst

case

If the costs for the PV battery are scaled up to 2000 inhabitants, the annual cost for 2000

inhabitants is £3M (Table 31). The upfront costs, which is the sum of the capital costs of the

system components and the PV plant is about £5M per year, (section 4.1.1.6) and about £35M for

the solar chimney. The solar chimney battery and the PV battery life cycle costs are £32M and

40M respectively. However considering that the PV battery is only storing during summer, this

cost is very high.


81 4.2.1.9.1 Kim T | 4.2.2 Helen F

4.2.1.9.1 Uncertainties

There are many uncertainties with these battery designs. A lot of the costs are estimated without

the real specification. For instance, the AC costs were estimated without knowing the exact size

and rating. Also, the backup generator for the NaS battery in the solar chimney case is assumed to

be required, although further study may reveal it is not.

NiMH, Li-ion, NaS and ZnBr are batteries that are not commonly used for PV application, they

are still immature and the development of the batteries may change their material requirements,

thus changing costs and performance. Other uncertainties are due to limited information available

since manufacturers protect their products from competitors. For instance battery capacities are

provided by the manufacturers who are not always easy to get hold of. Also, there are

uncertainties about applying battery storage to solar chimneys because there are no available

studies. There are however papers such as Rydh et al (2005) which recommend PbA or Ni-Cd as

the best battery option for PV applications.

Another problem is that there is no way of telling if these calculated costs are realistic because it

is difficult to find studies where prices can be compared. It is usually helpful to be able to

compare prices with existing technologies for validation. For further development and accuracy,

these storage models need to be modified to account for errors and incorrect values used. For

instance, for the PV application scenario (B), the actual peak usage is 4297kW per year and

6500kW for the solar chimney, scenario (B). Nevertheless, this analysis indicates that the PbA

battery is a feasible solution.

4.2.2 Seasonal Storage

The fundamental problem with using any of the conventional solar energy generation methods is

that as the daylight hours reduce during winter months in the UK which affect the energy

generated considerably, the electricity demand will increase (see section 3.3). One option is to

design the system to be able to generate enough electricity for the worst case winter day. It must

then store enough in short term storage through that day for the night when demand is higher.

This would be vastly expensive and in view of the costs of solar generation it would warrant the

scheme economically unfeasible. In the UK, the majority of solar technology is used only in

combination with another energy source or grid connected energy so that there is an alternative to

use during the winter or night time when there is a shortfall in the supply from solar. Considering

the storage options is therefore key in assessing the ability to provide the maximum feasible

amount of solar energy to power a town of 2000 inhabitants.

An alternative to this is having a long term storage solution. The long term storage system would

be charged over the summer period when supply is surplus to demand and used over the winter


82 4.2.2 | 4.2.2.1 | 4.2.2.1.1 Helen F

months when generation is not meeting demand. The peak demand this system would have to

meet is 758.3 kW (see section 3.3). This is a worst case and occurs at 18:30 on a winter‟s day

after the sun has set and the solar generator has ceased to generate energy. Refer Appendix

10.5.1.Part of this could come from short term storage so that the excess energy generated during

the day is not wasted.

The size and type of seasonal storage that can be used is primarily dependent on the required

storage capacity, the time it must be stored for, the output power capacity required and the method

of generation. Once a type of storage has been identified as the most appropriate, the location,

geology, cost, topography, land area and other environmental factors can influence the decision to

continue with that storage technology.

The storage methods can be divided into two types: electrical energy storage and thermal energy

storage. Electrical energy storage involves a method of transferring the electrical energy into

another medium, for example chemical energy (battery) or potential energy (water pumped

uphill). When it is required, it is converted back into electrical energy. Alternatively thermal

energy storage is the accumulation of thermal energy and requires a means of retaining this heat

for a long period of time, limiting leakage to a level that is acceptable. These energy storage

methods have been included and considered for application to solar chimneys, solar towers, PV

cells and troughs.

4.2.2.1 Seasonal Thermal Storage

A brief evaluation of the potential storage solutions for the solar tower and solar trough generation

methods were considered. However, they were not further analyzed because these methods have

emerged as the least economically viable of the four solar generation methods assessed and will

not be further developed to include storage.

The four main types of thermal storage are sensible heat, latent heat, heat of sorption and heat of

reaction. The latter two methods are relatively undeveloped, primarily because the energy density

(J/m2) which may be stored using heat of sorption and reaction is low in comparison to sensible

and latent heat. (65). Higher energy density methods of sensible and latent heat storage will

therefore be considered for seasonal thermal storage.

4.2.2.1.1 Solar Tower & Solar Trough Thermal Seasonal Storage Considerations

The solar tower and trough generators both release output thermal energy. Each of these

generating methods are likely to use a chemical medium such as water, paraffin or molten salt to

collect the energy and retail it for a period of several hours for short term storage. (66) These

chemicals are called heat transfer fluids and are investigated in section 4.1.4 and 4.1.3. Energy


83 4.2.2.1.1 | 4.2.2.2 Helen F

input is also required to keep the storage systems based on molten salt and paraffin running and

current systems using thermal storage tanks on the surface have a high energy leakage rate. This

makes these mediums unsuitable for long term storage.

Seasonal thermal storage in aquifers however, could prove to be an answer for solar thermal

storage. Figure 7 shows the output energy for a given input over the course of a year. The figures

appear favourable and in addition to the inputted energy, additional solar energy may be acquired

from the ground which has been heated by solar energy. This would be an area of further research

if thermal energy generation and storage was being considered.

Figure 52 - Histogram of monthly heat injection and heat extraction. Taken from (67)

4.2.2.2 Electrical Seasonal Storage Methods

Electrical storage methods are suitable for solar chimneys and PV generation types as their output

is electricity. Electrical storage would not be suitable for solar towers or solar troughs as the

primary output for these is heat and therefore a thermal storage method should be considered.

Although the intention is to convert the heat from the tower or trough generator into electricity, if

the storage is kept as heat storage, it will go through fewer energy conversions which incur losses

which will maximise the energy yield. Electrical seasonal storage methods will be applied only to

solar chimney and PV generation methods.

The electrical storage methods commercially available include batteries, capacitors, flywheels,

superconducting magnetic energy storage (SMES), compressed air energy storage (CAES) and

pumped hydroelectric storage. None of these methods are generally used for discharge periods of

more than 24 hours, let alone 6 months for seasonal energy storage - see Figure 53.


84 4.2.2.2 Helen F

Figure 53 - Graph to show optimal capacities and discharge periods for a range of commercially available

electricity storage methods. (68)

There is a possibility of using alternative storage methods for seasonal electricity storage which

are not currently commercially available. There is work being carried out in chemically bonding

hydrogen in liquid organic hydrocarbons (69), however this work is not at a stage of development

where it can be considered as a serious solution, with current maximum efficiencies estimated at

48%.

A number of the commercially available storage types are not suitable for long term storage due

to their daily rates of energy leakage, also referred to as „daily parasitic loss‟. Within a 24 hour

period, a flywheel will have lost 100% of it‟s energy. (70) Those with the smallest daily leakage

rates are pumped hydroelectric storage, CAES and Vanadium redox batteries. (70)

Vanadium redox batteries have been considered as a feasible long term storage solution and on a

very small laboratory scale have worked relatively successfully (71). However in a report of „the

potential of using these flow batteries with small scale solar plants‟, caution is erred as “further

work is required to translate the results achieved in the laboratory to a full-size battery.” (71)

Another flow battery that can be considered as an alternative is the zinc-bromine battery.

CAES is a method by which gas (air) in underground cavities is pressurised and depressurised to

store and generate electricity. A well known plant is in Huntdorf, Germany and is used for

leveling the daily energy fluctuations. CAES require increasingly expensive clear fuel such as

natural gas or distillate oil which provide 1%-5% of the energy that the system can store and

generate.(72) In addition the dependency on the correct geological situation for a successful


85 4.2.2.2 | 4.2.2.3 | 4.2.2.3.1 Helen F

CAES site rather limits the locations suitable for introduction of this technology. Areas for

consideration along the southern coast of England are mostly of chalk geology which is brittle and

unsuitable for CAES due to the fractures which occur. (73) The limestone bedrock can be found

100 m from the surface. In many areas this would mean drilling through 100 m of chalk or clay to

reach suitable rock for CAES. These reasons along with the possible dangers of leakage from the

caverns make CAES a highly risky and expensive method of storage when applied to the South

East of England.

“William Pickard who investigated the pros and cons of pumped hydro storage and CAES for

storing renewable energy and came to the conclusion that “underground pumped hydro ultimately

will prove to be superior.” (74)

Pumped hydroelectric energy storage will be considered as a potential long term storage solution

due to its small rate of daily leakage and because hydro-electric schemes have been successfully

constructed around the world. What will be different with this particular design is its storage

capacity. Instead of holding enough potential energy to generate for 6-8 hours, it will require

enough energy to discharge over the period of 6 months. The levelised cost of the storage facility

will be the deciding factor as although it is technically feasible, the capital cost could be too high

and may render the project practically unfeasible.

4.2.2.3 Pumped Hydro Energy Storage

A pumped hydroelectric storage system consists of two reservoirs at different heights. Energy is

stored by driving pumps which take the water in the lower reservoir to the higher reservoir,

raising the potential energy of the water. This potential energy can be „released‟ when the water

from the higher level reservoir runs through a turbine and back into the lower level reservoir.

4.2.2.3.1 Mechanics

The generation phase begins with water from the upper reservoir being let out through what is

called the penstock, which is simply a steel tube of a specific diameter, designed to allow the

water to run through the pipe work at a certain velocity. The water will run through the pipes

down to the turbine which powers a generator. See Figure 54


86 4.2.2.3.1 | 4.2.2.4 Helen F

Figure 54 - A representaion of the process of a hydr-electric pumped storage system (75)

To store energy, the reverse process occurs. A pumping turbine will turn and push the water uphill

from the lower reservoir to the upper reservoir. If a reversible turbine is used then the same

turbine and pipe work may be used. This reduces the capital cost of putting in the turbine and pipe

work and through reducing moving parts, the operating and maintenance costs are also decreased.

Savings of up to 30% have been recorded on capital costs by using the reversible units (75)

The energy used for pumping the water uphill is inevitably more than the energy produced when

the turbine is generating. This is largely due to the efficiency of the turbine and losses in the pipe

caused by viscous drag, water turbulence, pipe friction and evaporation rate.

4.2.2.4 Supply and Demand

The worst case storage scenario is in the winter months where a surplus of 4.462 MW is generated

during the day. During the winter, the 400 kW solar chimney option would generate a surplus of

4.462 MW during daylight hours and only 3.4 MW would be required from a seasonal storage

solution to provide the energy deficit. Note that additional capacity may be required here in order

to make up for the shortfall in the 4.462 MW from short term storage, as this is assuming an

efficiency of 100% energy turn around for the short term storage method. See section 3.3

If the short term turn around efficiency is 72% then there will be 3.213 MWh available energy

from the batteries during the winter.

The average hourly demand for a winters day is 443.2292 kW. Over the course of 24 hours this

sums to 10637.5 kWh or 10.6 MWh.

Much of this energy is provided by the operation of the tower during the day. 2.967 MWh is

provided. The amount required from long term storage is:

[55]


87 4.2.2.4 Helen F

To account for variation in solar irradiance of 5.2%, an additional 6% of the required capacity will

be included in the design figure for storage for the solar chimney, equating to:

[56]

Spread over the discharge period of 9 hours,

[57]

Over the 40 year period in which the plant is operational, a 15.56363% increase in power capacity

should be expected to account for expansion of the town. See section 3.3. The irradiance data also

varies so an additional 5.2%.

[58]

[59]

Finally, to calculate the total storage capacity, monthly demand data has been subtracted from the

monthly output data to find the seasonal deficit see Appendix 10.5.1. The period when the solar

chimney and PV plant cannot generate electricity is when the seasonal storage is used. For the

chimney the power required from seasonal storage is 890304 kWh, as shown in Table 32. A total

storage capacity of 900 MWh has been assumed to allow for expansion of the seasonal storage

requirement. These calculations have been repeated in order to obtain the peak output required for

the photovoltaic power plant, should mass seasonal storage be opted for. The results are given in

Table 32

Month Output - Demand (kWh) Discharge (kWh) Charge (kWh)

January -245189 -245189

February -149896 -149896

March 52305.96 52306.0

April 202964.9 202964.9

May 352661.7 352661.7

June 408010.1 408010.1

July 335538.8 335538.8

August 235455.3 235455.3

September 142027.6 142027.6

October -74076.1 -74076.1

November -175287 -175287

December -245857 -245857

Yearly Discharge (kWh) Yearly Charge (kWh)

-890304.9 1728964.4

Table 32 - Table to show calculation of seasonal storage requirement to support the solar chimney generation

method


88 4.2.2.4 | 4.2.2.5 Helen F

Generation

Method

Winter Daily

Surplus (MW)

Seasonal Deficit

(kWh)

Chimney 4.462 890304

PV 0.118 1042228

Trough n/a 835879

Tower n/a 1042975

Table 33 - Table to show long term storage requirements

The storage capacity for the hydro pumped storage in the chimney plant‟s case is assumed to

require a capacity of 900 MW for the course of 6 months. The storage capacity can be related to

the volume of water in the reservoir according to the equation:

= Storage Capacity

[60]

For a storage capacity of 900 MWh, a volume of 8,300,000 m3 of water would need to be stored.

This would need to be situated in an appropriate location where the area provides a higher altitude

and a lower altitude such as valleys, mountains, quarries or abandoned mines.

4.2.2.5 Turbine Choice

The turbine choice reflects the head difference between the two reservoirs and the discharge rate

per second. To attain a reasonable estimate of the turbine size, type and cost, a net head of 70 m

has been assumed.

Different turbines are effective at different flow rates and head values. Figure 55 shows the

relationship between these factors and the most common turbine types. A propeller turbine for

example is only effective for head differences of up to 10 m. A francis turbine has been selected

for this hydro pumped storage as the head opted for is mid range. Another option could have been

to use a Pelton or Turgo wheel, however the volumetric flow rate is 1.74 m3/s as shown in

Appendix 10.5.2 and would exceed the flow rate in which these turbines operate efficiently.


89 4.2.2.5 | 4.2.2.6 Helen F

Figure 55 - Optimum turbine choice varying with net head and discharge rate through the turbine (76)

More than one turbine will be required so that the plant can operate efficiently at a range of

different flow rates. They would be arranged in a series formation, similar to that in Figure 56

which helps regulate the flow.

Figure 56 - Arrangement of turbines to regulate the output/input flow (74)

The francis turbines are a popular choice for small hydropower projects and have been used

extensively in power generation. Many power storage projects in China have been recently

developed for numerous schemes for small villages (77). As a result, there are relatively cheap

200 kW packages available commercially which includes a turbine and generator unit on the

market. It would be economically advantageous to take advantage of this.

4.2.2.6 Geographic and geological considerations.

One of the primary difficulties with implementing a hydro pumped storage system is finding a

suitable location. Siting a suitable location for a reservoir is a challenge for several reasons; the

lack of uninhabited areas of land in the UK, the correct geology as impermeable rock is required

for the containment of a large body of water and the specific level change in the land required

within a reasonable distance whilst satisfying the previous two criteria.


90 4.2.2.6 Helen F

The water capacity required for an energy storage scheme of this scale is on the scale of a very

small reservoir at 8,300,000m3 of water compared to the proposed Thames Water reservoir which

will contain 100,000,000m3 of water (78). However siting a reservoir of 8,300,000m

3 is

challenging due to the South East of England being heavily populated. It should be expected that a

„perfect location‟ ready to fill with water will not be found and roads and/or buildings will have to

removed and relocated.

Nevertheless, a possible location for the hydro pumped system has been identified near Ringmer,

East Sussex. The location was deemed suitable because of the combination of the correct

geological features. As indicated in the map below, there is a valley with a small river running

through it which can provide a water source for the reservoirs. This would feed the reservoir to fill

it and negate the need to pay for the water to initially fill the reservoir.

Figure 57 - Map of Ringmer, Sussex and surrounding geography showing proposed location of the upper storage

reservoir and extent of reservoir walls. Taken and adapted from appendix 10.5.3.

Ringmer has ideal geology in that it is clay. According to the British Geological Society (BGS)

the area of Ringer “is an exposed Late Albian Upper Gault clay band which is dominant in the

immediate area running roughly east to west from Eastbourne to south of Petersfield.”(79) The

reservoir is situated on „Clay Hill‟ which would provide a naturally impervious barrier to stop

water from leaking from the reservoir. (South of Clay Hill lies Ringmer and a chalk pit). This

chalk pit could be used as the lower reservoir. The BGS records show that the chalk covers a vast

area around Lewis, just South of Ringmer. (79)


91 4.2.2.7 | 4.2.2.8 Helen F

4.2.2.7 Cost of Storage

4.2.2.7.1 Capital Costs

The main capital cost involved in the construction of a pumped hydroelectric storage system is the

construction cost of the reservoir. The Abingdon reservoir which is planned to be constructed by

Thames Water in Oxfordshire equates to a cost of £10/m3 of water capacity. (78) A study by Mott

MacDonald assessing potential costs of several reservoirs in Lamberhurst also estimated a total

capital cost equating to £9.1-9.3/m3 (80)

In comparison to the cost of the reservoir, the cost of the turbines is of very little significance. A

flow rate of 1.754 m3 has been assigned to the hydro storage for the solar chimney, and as shown

in figure 6, the cost of the francis turbine would be below £200,000. By keeping the flow rate

below 2.5 m3/s the turbine costs can stay reasonably low.

Figure 58 - Cost estimates for francis turbines vs flow rate for 50m head (81)

The penstock is another costly item which must be considered. Typically the penstock can equate

to 30-40% of the capital costs (82). Penstock costs will be assumed as 40% of total capital costs

for the purpose of this project.

4.2.2.7.2 Operating Costs

Operating costs covers annual costs for will consist of a constant yearly sum for small work

required such as cleaning, weed removal and annual inspections. For a small hydro scheme which

maintains a peak power capacity of below a megawatt, „one part-time operator is usually

sufficient‟. (83) An annual salary of £21,000 has been estimated for the operator.

4.2.2.8 Lifespan

The life span considered for the reservoir will match that of the generation design life. The PV

plant has an estimated design life of 30 years (see section 4.1.1), whilst the solar chimney has 40


92 4.2.2.9 Helen F | 5 group

years. However, due to the robust construction required for reservoirs, the actual life of the

reservoir will exceed both 30 and 40 years. After the initial construction of the reservoir, very

little work is required. Replacement and upgrading of mechanical parts can be carried out to

extend the design life of the mechanical and electrical equipment. This carries a very small

portion of the overall cost. The reservoir wall should be surveyed to ensure it has not endured any

damages or deterioration over time. This should happen at the annual inspection. If maintenance

of the structure is carried out rigorously then the life span of the reservoir should extend far

beyond the 30 - 40 year life span of the solar chimney and the PV power plant.

4.2.2.9 Development Time

A hydro facility of this size would require a development time of 2 to 5 years to allow for

environmental studies, approvals and several levels of feasibility studies. (83).

5 Analysis

In order to determine if solar generation is a feasible method of electrical production the results

the Section 4 are compared against each other and analysed.

5.1 Generation

The comparison of the various methods of generation discussed in section 4.1 is shown in Table

34; methods are compared by key information common to all such as cost and dimensions.

PV Solar

Chimney

Solar

Tower

Solar

Trough Coal Nuclear

Life span (years) 30 40 30 25 - -

Area (m2) 190,139 2,243,175 292,515 32,000 - -

Efficiency 17.3% 0.63% 14% 11.5% - -

Peak Output (MW) 35.4 6.5 3.25 2.02 - -

Av Annual Production (GWh) 13.37 12.04 3.15 3.5 - -

OM cost (£Thousand/y) 2,336.4 428.8 491.6 136.2 - -

Capital cost (£Mil) 11.18 33.78 74.5 54.2 - -

Levelised cost (p/kWh) 21.5 10.6 83 68 10.5-13.8 10

Table 34 - Comparison of electrical generation methods comparing key features of each based on new builds

starting after 2009 (17)

Only Solar Chimneys have a levelised cost less than the average consumer cost of electricity of

13p/kWh, meaning it has a potential for profit. This method is also more financially feasible than

building new coal or nuclear power plants due to the increased cost in construction and carbon tax

associated with them in recent years (17). PV, Solar Towers and Solar Troughs however, have a


93 5.1 Group

much higher levelised cost and as such are not financially viable with the current construction and

OM costs associated with them.

Based on levelised cost a solar chimney plant, discussed in 4.1.2.5, is the most feasible option for

generation. This cost however, does not take into account the size and cost of the land plot needed

to construct a plant. Solar chimneys require vast areas of land in comparison to PV and other

forms of generation, due to their low efficiency. Based on a land cost of £1.23 per m2 in the South

East (84) the cost of land required was calculated and is shown in Table 35. As shown the

purchase of the land only affects the solar chimney plant, however this land can continue to be

used whilst part of the plant as discussed in section 4.1.2.4.

PV Solar

Chimney Solar Tower Solar Trough

Land Cost (£) 54324.18 2759105 359793.5 39360

Levelised Cost (p/kWh) 21.5 11.25 83 68

Table 35 - Cost of land plot for each method of solar generation and its effect on levelised cost

The irradiance data varies over time, as does the generation meaning supply does not follow the

trend of demand, as shown in Figure 6 and Figure 4. As a result short term and in some scenarios

long term storage will be required, the use of these is evaluated in section 5.2. The addition of

both short and long term storage significantly increases the cost of the system from a levelised

cost, most notably in PV where an increase 14p/kWh to 390p/kWh was observed. In order to

remove the need for seasonal storage the plant must either over produce or be supplemented by

an alternate supply, such as the grid, see section 4.1.2.5. By removing seasonal storage levelised

costs can be reduced however power must either brought from an external source to fill the deficit

or the surplus sold externally, both of which may affect feasibility.

The ability of each generation method to survive in the British climate is also a factor effecting

feasibility, Solar Troughs and Solar Towers are both complex systems with finely calibrated

moving parts, the performance of which will deteriorate over time with climate effects. These

methods will require constant maintenance and calibration to counter wind effects and

weathering. Solar chimneys and fixed angle PV plants are much more resilient to climate effects,

the solar chimney will require a concrete cover depth of approx 30mm or more in order to survive

extended weather exposure. All of the discussed plant designs will sufferer from high wind

loading due to the large surface areas inducing high pressures and as such with require correct

grounding. The most feasible plant design in terms of durability to climate would be the solar

chimney and PV plant due to the simplicity of design.


94 5.1 | 5.2 Group

The average domestic cost of electricity for 2011 is estimated at 13p/kWh, section 3.4.3, as such

the sale price of the generated units must be able to compete with this price. Excess electricity

exported will have to be sold at competitive rate. Based on a domestic sales price of 13p/kWh and

export price 11.5p/kWh the NPV for each generation is shown below in Table 36. The export rate

was chosen based on a generation levelised cost of approx 10p/kWh in line with a coal or nuclear

plant built in 2009. This value would vary unfavourably over the course of the year with demand,

resulting lower cost in the summer period where production is at its peak and higher costs during

the winter where there is little production.

PV Solar Chimney Solar Tower Solar Trough

Discount Rate 7% 10% 8% 10%

NPV -23,663,624 -23049415.2 -27,227,918 -51,904,124

Table 36 - NPV values for various methods of generation and their associated discount rate

As PV is more widely tested and several commercial PV plants exist in Europe and climates

similar to the UK it has a lower discount rate compared to the other methods. The other forms of

generation have higher discount rates as they are all untested in conditions similar to the UK and

some of the technologies are new. The NPV values for of the forms of generation are largely

negative with Solar chimneys have the highest of the NPV‟s; these values indicate solar

generation is an unfavourable investment.

Considering all the forms of generation investigated, solar chimneys are the most feasible; with a

low levelised cost it is possible to generate a profit, as shown in Figure 25. Other generation

method either have too great a construction cost compared to production, such as Solar Troughs

and Solar Towers, or the OM absorbs all profits as is the case with PV.

5.2 Storage

Storage is a key aspect of the evaluation of the feasibility of solar generation. The viability of both

short and long term storage will determine the design and method of generation as well as

affecting the final cost associated.

5.2.1 Short Term

5.2.1.1 Efficiency

The most efficient battery is Li-ion with the highest possible efficiency being 95%. The lowest

efficiency is 60% for ZnBr. However, these two batteries, including NiMH are not viable to use

for the two solar electric generation systems because their rated power is low (see Table 26). The

batteries are required to store between 7MW to 10MW in the solar chimney case. Ni-Cd is also a

very high efficient battery, but the capital costs and operating costs are high. Although it requires


95 5.2.1.2 | 5.2.1.3 Group

fewer replacements than PbA, it is anticipated that the life cycles costs will be high because of the

high capital costs (Appendix 10.4). The overall efficiency, with the charger, battery and inverter

included, is 72% for both the PV plant and solar chimney.

For the PV application, PbA, Ni-Cd and NaS initially seemed like the best option. However after

analysis, it was noted that the rated power of NaS was out of range. The batteries in this case are

required to store only about 9kW to 10kW of power depending on the battery. It would have been

beneficial to also analyse Li-ion to see how it completes with PbA and Ni-Cd. However, this

would require more time to evaluate.

5.2.1.2 Depth of discharge and Service Life

The DOD of a battery determines the service life of a battery. The DOD for the batteries was

80%. Table 37 shows that NaS has a very high service life of 13 years. Ni-Cd lifespan is very low

and PbA has the worst. This cases the costs to rise when the life cycle costs of the whole plant are

calculated, due to the constant replacement. However, the lifespan of the chimney battery increase

because the DOD is reduced in summer (see section 3.3)

This is a different situation for the PV plant battery storage. The battery only runs in the summer

at 80% DOD. During winter the battery is not in use but it is important to leave the battery fully

charged otherwise the electrolytes will dry out. Although the battery service life for the PV

application had initially been calculated to be 2 years, this estimation is incorrect (see Table 37).

Take note that this needs to be amended because it was based on the same assumption as the

chimney battery that it would be going through 365cycle/yr or in other words 1 cycle a day. This

is not true for the PV battery because the battery is only operating for the 3 months in summer and

the rest of the time it is not in use and contains stored energy. So operating the battery for

90cycles/yr will give the following life cycle:

Component N80 σ(T) Service Life DOD=80% Service life (for 90 days)

PbA 1000 0.69 1.9 8

Ni-Cd 1500 0.9 3.7 15

NaS 5000 1 13.7 56

Table 37 - Corrected service life for PbA for the PV application

5.2.1.3 Costs

The remaining options for the chimney were PbA and NaS, and PbA and Ni-Cd for the PV

application. NaS although a competitive option is not viable because of the unsafe operating

conditions and the cost was slightly higher than PbA. Therefore, the most suitable battery in both

cases is PbA. The annual costs and life time costs are shown in table 8 and table 9. The total cost


96 5.2.2 Group

for the first year of use, based on the assumption that the NPV value is zero for subsequent years,

is nearly £2,000,000 for the chimney and £4,000 per household for the PV application (see Table

27Table 30) (Khu, S.T email conversation with Kimberley Tapfumaneyi 7/01/2011). The

different scenario used to analyse the two generations make it difficult to compare the two

batteries for the generations. This is because different factors have been used due to different

assumptions made, (see section Short Term Storage). Hence, the different costs for the storage

modified generations and the total system costs in the storage section. Also, complete analysis of

the whole project concerns such as the modified costs for the generations where different. (see

section 4.2.1 and 4.1).

Finally, the costs for the solar chimney and PV plant batteries were based on costs of one scenario

from the short term storage. This is an area of uncertainty because the cost will vary for scenario

to scenario because the capacity of the batteries and the peak output will change. Therefore, this

will affect the levelized costs of the technologies.

5.2.2 Seasonal

Hydroelectric pumped storage was chosen for a seasonal storage solution due to its theoretical

feasibility assessed in section 4.2.2. By applying the constraints and variables discussed in section

3.2 a numerical model could be created to analyze the feasibility of seasonal storage with a range

of scenarios. The scenarios have been identified as A, B and C in section 4.1.2.5 and 4.1.1.9

where:

Scenario Storage Scenario

A Long term and short term

storage used

B Only short term storage used

C No storage. Plant supplies

demand directly.

Scenarios A and B will be analyzed in this section for use with both solar chimneys and the p-v

plant as scenario B and C have identical storage scenarios.


97 5.2.2 Group

Figure 59 - Histogram to show total cost of a pumped hydro storage facility for a year periof

Figure 59, , as expected, shows that the capital cost of the storage facility is vast. The operating

costs however are minute in comparison. The capital costs here does not yet include the price of

the land. The increased capital cost due to land purchase is shown in Figure 61.

For purpose of direct comparison, costs have been compared for a 40 year period and so the P-v

plant costs which originally had a design life of 30 years have been scaled up to measure directly

with the chimney which has a design life of 40 years. The capital costs of hydro pumped storage

are relatively high in comparison with the cost of operating the plant thereafter, so it seems a

reasonable assumption that a more cost effective solution would be to spread the design life of the

chimney over an increased number of years, as shown in Figure 60.

Figure 60 - Graph to show the effect of increasing the design life on levelised cost

To meet the differing power capacities required by chimney and p-v plant the volumetric flow

rate, number of turbines, penstocks and generators is different between the plants to avoid having

a different head for each example which would impact on location.


98 5.2.2 | 5.3 Group

Figure 61 - Histogram to show the total cost of storage for scenario generation discussed in 4.1.1.9 and 4.1.2.5

The cost of land when calculated ranged from £86,100 to £2,765,000 and has been included in the

calculation of the total cost for each storage scenario in Figure 61. The most economically

feasible storage scenario is Chimney scenario B which benefits from low capital costs and

operating costs and a reasonable energy yield (Section 4.1.2.5). The costs do not increase

significantly when scaled up to meet the requirements of scenario B where the plant must be able

to meet a higher power output to ensure there is no overall energy deficit in the winter months.

The increased cost of meeting scenario B is less than the capital cost of the seasonal storage

facility. Implementing a seasonal storage solution for the chimney is therefore not beneficial.

The costs of p-v power plant are also dramatically reduced for scenario B. Again, increasing the

size and power capacity of the power plant is a more economically feasible solution to meet

Winter demand than building a seasonal storage facility for a design life of 40 years. This is down

to the enormous capital costs involved in building the reservoirs. Although there are other storage

methods available for storage, section 4.2.2 found no feasible alternatives for a 6 month discharge

period at the power capacity required, an electrical seasonal storage method seems to be

unfeasible at this time.

5.3 Complete System

The most feasible solar generation system evaluated in section 5.1 consists of solar chimney

generation combined with short term battery storage as discussed in section 5.2.1 without seasonal

storage. The Chimney design recommended is that of scenario B shown in Table 14 with lead acid

batteries delivering a practical usable capacity of 4500kWh and actual capacity of 7860kWh for


99

nocturnal distribution. This capacity of storage is based on the winter nocturnal requirements of a

village and is design for overnight delivery.

For a real plant a mid-term storage would also be required to store up to a fortnights electrical

requirement for the village to of 2,000 in order to buffer for fluctuations in irradiance and poor

weather periods. This could be done using batteries however due to the capital and short life cycle

a small hydro-electrical system should be considered such as a water tower with a generation and

pump system.

Due to the vast capital required, seasonal storage was deemed impractical. It is more financial

feasible to construct a much larger plant capable of generating the power required by the village

all year around. The excess power can be sold on for a small profit allowing for extra revenue to

be accrued. Further profits can be amassed by using the area under the collector to house various

business spaces as discussed in section 4.1.2.5. By using the collector as a natural greenhouse and

renting the agricultural land underneath an additional profit of £9.6 Million can be obtained. The

financial analysis of the complete system can be seen in the electronic appendices attached. A

recommend construction gantt chart for the complete system can be found in Appendix 10.6.

The levelised cost of the plant is proportional to the lifespan, the stated project duration of 40 is a

conservative estimate, the chimney being concrete and steel will last at least 60 years, the

collector structure is steel and can also be treated and maintained to last 60 years as well. The

collector roofing and turbines will however require replacing during a 60 year lifespan, despite

this, the levelised cost can be dramatically reduced. The effect of varying plant lifespan on

levelised cost can be seen in Figure 62

Figure 62 - Effect of variation in life span on levelised cost for a solar chimney power plant

0

0.05

0.1

0.15

0.2

0.25

20 25 30 35 40 45 50 55 60

Leve

lised

Co

st (

£/kW

h)

Lifespan


100 5.3 Group

As shown a longer lifetime equates to a lower levelised cost, the chimney is initially tasked to a

40 year lifespan however if at the end of this period, the use of plant can be extended relatively

cheaply via the replacement of the turbine, collector roof and maintenance on the collector

framework.

6 Discussion

Many types of renewable energies in the UK do not qualify for feed in tariffs. Of the four main

types of solar power generation evaluated within this report only photovoltaic solar panels qualify

for the tariff. Due to the size of the proposed solar plants in this report only scenario C (summer

production only with small winter production) is small enough to qualify for the top bracket of

funding. The peak output is 4297kW (with the maximum plant size being 5MW) generating 29.3p

of revenue per kWh sold to the National Grid. Unfortunately a review of feed in tariffs is due in

2012 so the scheme may not continue making the cost of going greener greater and for many not

economically viable.

When building a power plant near a residential area the opinion of the residents must be

considered. Many residents will be unlikely to approve a large industrial complex in close

proximity to their dwelling. Measures can be taken to help improve public opinion of the plant, or

alternatively to hide or disguise it in order to appease residents. PV plants are relatively low,

reaching only a few meters in height and can be easily concealed from view with hedges or trees.

Solar Chimney plants however are much taller and would not be possible to conceal, rather than

hide the chimney it would be possible to design an aesthetically pleasing chimney with a viewing

platform and access incorporated. The collector can also be used to incorporate community spaces

and sports facilities to appease local residents as discussed in section 4.1.4.5.

The traditional design of the solar chimney is simple, industrial and is seen as being an eyesore.

Architects are beginning to produce designs that attempt to combat the imposing features of the

towers and ways of utilising the vast area of covered space under the transparent canopy

surrounding the chimney to create the convection current. The towers are being designed with

elaborate viewing platforms to maximise the views available at the top of the chimney. Also large

decorative sheets and sections can be used to break up the tower giving it an interesting and

modern look.

Under the chimney will be approximately 2.2 km squared of flat land that has a number of

different uses. The land towards the centre of the chimney will be warmer and the convection

current will gain some speed so will not be suitable for general use. Proposed in the appendix are

sports grounds and agricultural lands that would create revenue and contribute to lowering the


101

levelised price per kWh. One other conceptual idea that has been proposed is to construct small

towns (and eventually cities) under the canopy. This would mean that only small amounts of land

would be lost in using a solar chimney as a method of sustainable power production.

The use of solar power as a method electrical generation will become increasingly feasible in the

immediate future; this is due to improvements in generation technology most notable solar towers

and PV, combined with the increasing levelised cost for new coal and nuclear plants (19). The

introduction of carbon tax will also serve to increase the unit cost for more traditional combustible

forms of generation, making levelised costs for solar power competitive. Based on predictions

from (19 the levelised costs for coal will reach 0.14 £/kWh by 2023 (cost is without inflation and

cost is due to increasing fuel costs and increasing carbon tax), meaning solar will be a much more

profitable and a feasible source of generation.

The loss of energy during storage is an important factor to consider. The loss of energy is

measured by a discharge rate and depends on temperature and the chemistry of the cell. Over long

periods of time batteries will self discharge. PbA self discharges at a rate of 4% to 6% per month.

So over 9 months which is the longest period the battery is out of use for the PV scenario (X) the

battery would have lost only at least 54% of its stored energy. If the battery is discharged below

20% (44), the electrolytes will dry out or decompose the chemical content. The discharge rate for

Ni-Cd for instance is even higher at 15 to 20%. This means the battery will be completely drained

by the end of winter. The second option is to increase the capacity of the battery but this would

not be beneficial because Ni-Cd capital cost is high. So the loss in storage will not affect the

chimney because the battery is used throughout the year.

Lead acid batteries are very environmentally friendly because 97% of the battery is recyclable.

The plastic from the battery is reused to make new battery cases and covers. The lead is recycled

and used for new grid. The lead ingots are used to make grids and the sodium sulphate from the

electrolytes are both sold and used in textiles, detergents or glass (Battery Council International).

Lead acid have very low costs however other costs for batteries such as Lithium batteries will

start to fall as the technology becomes more developed. However, the target is $300 per kWh

which is still too far to reach because the battery ranges from $600 to 1200$/kWh. The only

current benefit Lithium batteries have over lead acid is the lifespan, thus compensating for their

high costs (80). However, despite the low costs of lead acid it is a massive downfall when applied

to the generation costs because it greatly affects the levelised costs.

Short term storage is a requirement of all solar power plants in order to provide uninterrupted

power; this is due to the lack of available sunlight for night time generation. It is possible however


102

to store water bags under the solar chimney collector in order to store energy in the day and

release it a night, allowing for 24 hour production. This method of nocturnal generation can be

implemented cheaply requiring the only the purchase of sealed water sacks. This would eliminate

the need for expensive short term battery storage and increase the profitability of the plant.

Another consideration would be to remove short term storage for nocturnal demand and rely on

existing traditional generation and distribution systems to power the village during night hours.

The solar plant could be sized to produce enough power for the village during the day, export the

excess produced and switching to the national grid supply after dark. The cost of nocturnal supply

would be entirely covered by the customers and the exported energy would increase revenue,

overall reducing the OM costs and maximizing profit.

A benefit of using a solar chimney solution for energy storage is its ability to be recycled. If glass

or recyclable plastic is used for the greenhouse windows, most of the roof can then be recycled.

The steels connecting them can also be melted down and reformed for other uses. The tower itself

cannot be reformed in the same way as the glass, plastic or steel, but could be reused should the

plant be discharged at the end of its design life. The tower could serve a purpose as a cooling

tower for example, should its rate of deterioration be acceptable. If not it‟s rubble could be used as

recycled aggregate or hard core, should it meet specifications, for other construction projects.

Work has been done on methods of recycling PV cells where it has not on solar chimneys,

partially due to PV cells having been a relatively mainstream technology for some time. In July

2007, the European PV industry established a „PV cycle‟ a signed up to achieves certain goals by

2013, including “a minimum of 65% of PV modules installed in Europe since 1990, and recycle

85% of waste.” (88)Most parts of the PV cell can be recycled. The metal frame and circuitry can

be melted and recovered. The smelters doing this work benefit from the silica in the glass which

they would use directly for part of their smelting operations. (89)

The solar chimney and PV components can be dismantled and recycled relatively easily, however

the battery storage poses more of a challenge due to the toxic metals used for storage. The same

problem is experienced by solar towers and solar troughs which require toxic molten salts to

collect the thermal energy. Molten salts are harmful to skin and are also hazardous when inhaled.

(90)Consequently decommissioning costs for the tower and trough thermal power plants could be

expensive.

The chimney structure could have a significant impact on its success in planning stages. For

instance an industrial concrete „steam tower‟ like structure would be considered an eyesore,

particularly as the site is likely to be located on agricultural land in a rural area. Careful design


103 6 | 7 Group

involving blending the rather large chimney structure into the local environment by curving the

tower and roof structure could be the key factor that influences public opinion. At an additional

cost, the tower could be partially clad in steel or glass to reflect light, which could have the effect

of „blending‟ the tower into the sky.

Optimising the shape of the structure to appease public opinion would however have a structural

affect and additional loadings would have to be considered. It could also improve the structures

stability, for instance changing the roof curvature could reduce the wind loading on the roof,

making the construction costs more favourable. Additional construction detail such as a self

cleaning coating will reduce maintenance costs considerably. Further optimisation could yield

further cost savings.

In a bid to be more competitive solar tower and solar trough generation can provide a portion of

the heat energy required by the village of 2000 people. Both of these methods produce substantial

amounts energy and some of this energy is lost to the environment. Providing heat energy for the

village can be achieved by using a heat integration or heat recovery system. The system works by

recovering heat from hot streams with potentially high energy content such as the steam from the

condenser. This recovered heat can be used to pre-heat the heating water that will be used by the

village.

7 Conclusions

It is the conclusion of this study that, based on the values obtained from section 5, electricity

generation with solar power is feasible for a village of 2000 inhabitants. A shown, solar chimneys

can commercially compete in the open market, chimney with a levelised cost of 10.6 pence/kWh.

However due to the long return time, high capital required and negative NVP, solar generation is

not currently a desirable investment.

Other forms of generation, namely solar troughs and towers, were discounted due to high capital

or the need for long term storage. The most viable options for storage within this report are the

hydro-electric dams. These have massive capital costs that were unable recoup over the lifetime of

project with the levels of revenue used.

The land under the solar chimney canopy can be practically used for such purposes as farming

without affecting production. as the increased temperature in the area under the canopy is at a

higher temperature than outside and could therefore be rented out at a favourable rental price.

This is a unique advantage of solar chimneys over other forms of generation and as such further

research into its practical uses is recommended.


104 7 | 8 Group

The most prominent problem with current solar generation is the lack of nocturnal production, as

such additional storage is required for the short term which negatively effects the economic

feasibility of solar generation. It was concluded from the results obtained that whilst short term

storage is financially feasible, long term is not with the current design life of the projects

considered. If a solar generation is to be practically implemented a mid-term storage system will

be required in order to account for variations in irradiance that is not absorbed by the generation

excess buffer.

The solar chimney, should its performance be proven, would be a robust technology in the face of

time. Unlike PV which requires the replacement of PV cells at the end of their design life, the

concrete tower should it be constructed with care should last longer that the 40 years stated, with

only minimal replacement of moving parts in the turbine and generator.

Based on the trend in increasing levelised costs for traditional forms generation coupled with

carbon tax it is predicated that solar generation will become more competitive. Due to advances in

solar generation technology, the levelised cost for solar generation should reduce whilst the cost

for fossil fuel based energy generation will increase. As a result the statement that solar

generation is feasible will remain valid for the immediate future.

This report has a limited scope of study, as such future research is recommended. Areas not

covered in this study that would require an indepth study are the environmental policy and

legislation concerning power plant construction, the decommissioning and recycling necessary

once a plant reaches its design life and the effect of variation in the economy on the feasibility of

solar generation.

8 Recommendations

The construction of a Solar chimney and short term storage system should be constructed in the

South East UK to supply a village of 2000 people with electricity at a minimum unit cost of 10.6

pence/kWh.

Due to the economies of scale it would be more financially viable to supply a village of 20,000

people with electricity rather than 2000 people. The construction of a higher chimney would

vastly increase the available output and would reduce the unit price.

Long term storage is not recommended due to the large capital costs. If the design life of the long

term storage could be guaranteed for longer (above 200 years) then this would become more

realistic and lower the unit price. Further investigation and analysis needs to be undertaken to


105 8 Group

determine if this would bring the unit price down to a point that would make it competitive with

scenario B and traditional methods of power generation.

It is not advised to construct solar troughs and solar towers in the South East UK to supply

electricity. A method of using these systems to supply a village of 2000 people with hot water and

heating a require investigation in a further study.

Solar PV is not currently competitive with the commercial energy market based on the best unit

price of 21.5 pence/kWh. In the future, rises in energy prices and the recent addition of Carbon

tax may make solar photovoltaic competitive.

Storage is the main drawback when using solar power as a sole means of power supply. Where

possible the use of storage should be avoided within reason.


106

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86. Technical Manual for lifeline Batteries. [Online] September 2009.

http://www.lifelinebatteries.com/manual.pdf.

87. UK Energy Research Centre. Making the transition to a secure and low-carbon energy

system: synthesis report. April 2009.

88. Department of Energy and Climate Change. Quarterly Energy Prices. s.l. : National

Statistics, September 2010.


113

89. Telford, Thomas. Enviromental Impact Assessment - A guide to procedures. s.l. : Department

for Transport, Local Government and the Regions, 2000.

90. Mott McDonald. UK Electricity Generation Cost Update . Brighton, UK : s.n., June 2010.

91. Richardson, Coulson &. Heat transfer equipment. Chemica lEngineering Design. s.l. :

Elsevier Butterworth-Heinemann, 2004, pp. 637-640.

92. Thorpe, .R. B., Thorpe and C., A. Millington. Design Project 2009-10, Bio-Ethanol,

Version 2.2. Guildford : University of Surrey, 2010.

93. P.J.Donalek, Senior Member. Role and Value of Hydro and Pumped Storage Generation in a

Proposed Regional Electricity Market in Southeast Europe. s.l. : IEEE, June 2003.

94. Lawrence Kazmerski, National Renewable Energy Laboratory (NREL). Wikipedia PV

efficiency. [Online] September 2010. http://en.wikipedia.org/wiki/File:PVeff(rev100921).jpg.

95. Greenemeier, Larry. Scientific American. [Online] December 2009.

http://www.scientificamerican.com/article.cfm?id=hybrid-solar-panels.

96. Small Hydro Project Analysis Module RETScreen. Minister of Natural Resources Canada.

2001-2004.

97. Electropedia. [Online] http://www.mpoweruk.com/performance.htm.

98. Electropedia. [Online] http://www.mpoweruk.com/life.htm.

99. Electrical Energy Storage. University of Colorado Boulder. [Online] [Cited: 18 December

2010.] http://www.colorado.edu/engineering/energystorage/ .

100. Battery Council International. Battery Recycling. [Online]

http://webcache.googleusercontent.com/search?q=cache:CoGqrrfF7xYJ:www.batterycouncil.org/

LeadAcidBatteries/BatteryRecycling/tabid/71/Default.aspx+lead+acid+battery+recycling&cd=8&

hl=en&ct=clnk&gl=uk&client=firefox-a.

101. Alternative Energy. [Online] August 2010. http://www.alternative-energy-news.info/pete-

process-technology-fusion/.

102. Price, H., Luepfert, E., Kearney, D., Zarza, E., Cohen, G., Gee, R., and Mahoney, R.

[book auth.] International Journal of Solar Energy Engineering. Advances in parabolic trough

solar power technology. 2002.


114


115

10 Appendix

10.1 Solar Chimney

10.1.1 Derivation of turbine efficiency

10.1.2 Design and Cost of Solar Chimney Construction

The cost of the solar chimney collector based on the design shown in Figure 17. The roof is

support by a steel frameworks, anchored in the ground at 9 meter intervals, this 9x9 spacing

provides a good compromise between price. Based on a 9x9m support structure the cost of

collector has been estimated at £9.2m2, this cost covers the plastic roofing, the steel support and

concrete used to ground it.

10.1.3 Solar Chimney Collector for use as a Sports Facility

The solar collector can be used as a covered sports facility, in order to achieve this as cheaply as

possible only court and pitched facilities will be built as these require minimal staffing and

maintenance. For the sports facility it is suggested that the following facilities illustrated in Table

35, with net guarding to surround the court and protect the collector could be built and maintained

with a single staff member monitoring admissions and equipment hire. It is noted that in order to

use the collector with sports facilities the collector roof should be at a height of over 4m, this is

within the suggested limits of 2-8m in (24).

Facilities Quanitiy Unit cost (£) Description

Tennis Court 3 4600 Grass surface, painted

white boundry lines,

basic posts and nets with chainlink

surround fence

including gate

Badmitton Court 2 4600

Bowls green 1 500

Hocky pitch 1 6500

Football pitch 1 6500

Table 38 - Basic capital cost for each sports facilitie

10.1.4 Solar Chimney Collector for use as commercial greenhouse rental

The Collector acts as a greenhouse, and as such can be used for agriculture; however only the

central region will be comparable to commercial greenhouses. The outer region of the collector

will be too cold due to its proximity to the air inlet; the central region during hot summers will be

too hot for agricultural uses. It has been estimate that the region illustrated in Figure 63 is viable

for agricultural use.


116

Figure 63 – Area of collector available for use with agriculture

In order to attract customers it will be necessary to provide irrigation and access to water and

power, it is assumed power can be supplied from the plant its self and water collected from the

collector, stored in butts, filtered and redistributed. Irrigation can be cheaply supplied via a drip

irrigation system connected to the butts and a pump. The UK has an average rainfall of ~960mm

annually and the large area of the collector can be used to gather this water. Paving will also be

supplied to separate 10M wide plots of 40M length where an annual rent of £1/m2

is applied for

the agricultural land. The capital cost of fitting a drip irrigation system, cabling and paving are

shown in Table 39. It is necessary to replace the irrigation piping after 20 years as well as the

power cabling.

Material Cost (£/m2)

Water Butt Storage + Filter 3

Drip Piping 2

Piping Pegging 0.7

Pumping 0.2

Floor cloth for weed control 0.6

Paving (for 10X1m have 0.4x1

paving) 3.97

Drainage 0.75

Power Cabling 0.15

Table 39 - Basic costs per square meter for agricultural renting business equipment


117

10.1.5 Costing associated with solar collector

The basic financial information concerning solar chimney with and without the additional sources

of revenue such as the hot house letting scheme and sports facilities are shown in Figure 64.

Plant Plant with Sports Facilities

and Hot House Letting

Annual Output (GWH) 12.04

Revenues

Domestic Sales (@13p/kWh) 390261.6

Export Sales (@11.5p/kWh) 1039125.8

Capital (£Miilion) 33.78 41.7

OM (£/annum) 439,022 531,463

Pay Back Time (years) 36 32

NVP (@10%) -23060406.6 -26115132.0

Residual Value (after 40 years) 8340799.27 11863224.68

Figure 64 - Basic financial information for solar chimney with and without additional revenue sources


118

10.2 Alternatives

Figure 65 - The development of PV Technology (Lawrence Kazmerski 2010)

http://upload.wikimedia.org/wikipedia/commons/7/74/PVeff(rev100921).jpg


119

10.3 Solar Tower Power Plant

10.3.1 Table of Values for Solar Tower

A list of the values used to perform the chemCad simulation and pricing estimates are given

below:

Heliostat

Area of one Heliostat = 90 m2, total number of heliostat = 217

Cost of heliostat (Mancini, 2000) = 456$/m2, therefore total cost of Heliostat = $8,905,680

This is cost of heliostat in the year 2000, therefore price in 2010 = Cost index (Cost indices,

2010) in 2000 = 394.1, index of November 2010 = 525.6

Therefore price in 2010 = (525.6/394.1)× 8,905,680= $11,877.253

Therefore dividing by this month exchange rate = $11,877.253/1.58 = £7,517,249

Tracking system

There 217 solar tracking system each costing 7630 Euros (Mecasolar, 2010), therefore total price

= 217×7630 = 1,655,710 Euros = 1,655,710 /1.18 = £1,403,144

10.3.1.1 Tower

Exchange rate (Times, 2010) = 1.58 this is the

Height of Tower = 60m, length of tower = 15m, width 15m

Price of concrete = $80/m3

Bare cost of tower = $80×15×15×60 =$1,080,000

Therefore cost in pounds = 1080000/1.58 = 683,544

10.3.1.2 Receiver

The receiver is a larger heat exchanger in which air is heated, to generate steam. It is important to

size this heat exchanger in three sections since phase change is occurring. Also the heat transfer

coefficient for each stage in the heat exchanger will be different.

First section


120

Temperatures also obtained from ChemCAD

U for air and condensate = 150

T1 hot fluid temperature inlet = 1842

T2 hot fluid temperature outlet = 1330

t1 cold fluid inlet = 33

t2 cold fluid outlet = 275.5

Overall heat transfer coefficient = 150

F = 1

∆T1 = T1 – t2 = 1842 – 275.5 = 1566.5 °C

∆T2 = T2 – t1 = 1330-33= 1297 °C

C

T

T

TTTLM

5.1427

1297

5.1566ln

12975.1566

1ln

2

21 = 1428

Typical heat transfer coefficients were found in (Richardson, 2004) table 12.1.

U = 150W/m2 °C, heat load in this section = 3800 kW

Thus the area is calculated:

21815.1427150

10003800mA

Second section




t1 cold fluid inlet = 275.5

t2 cold fluid outlet = 275.5


∆Tlm = 578

Q required for phase change = 5500

Therefore = 248

1578200

10005500mA

Final section


121




t1 cold fluid inlet = 275.5

t2 cold fluid outlet = 440


∆Tlm = 24.87

Q required for phase change = 1700

Area = 342

Therefore total area = 342 + 48 + 18 = 408 m2

Bare vessel cost (Figure 7.18) (A.M.Gerrard, 2000) Purchased cost = £90,000

the cost in 2000 = £90,000, therefore price in 2010 = (137.6/100) ×90,000 = £123,840

10.3.1.3 Turbine

The maximum average power input = 3250 kWh/day

From figure 7.19 (A.M.Gerrard, 2000) the cost in 2000 = £2,100,000, therefore price in 2010 =

(137.6/100)*2,100,000 = £2,889,600

Therefore total delivery cost of compressor in 2010 = £2,889,600

10.3.1.4 Generator

Approximately same price as turbine = £3,000,000

10.3.1.5 Condenser

In order to cost the condenser it will be appropriate to find the area, therefore heat load on heat

exchanger from ChemCAD simulation

Q = 7740 kW

T1 hot fluid temperature inlet = 33°C

T2 hot fluid temperature outlet = 33°C

t1 cold fluid inlet = 22°C

t2 cold fluid outlet = 31°C


122

A = Q / LMT × F × U

Temperatures also obtained from ChemCAD

∆T1 = T1 – t2 = 33 - 31 = 2 °C

∆T2 = T2 – t1 = 33-22= 11 °C

C

T

T

TTTLM

3.5

11

2ln

112

1ln

2

21

Typical heat transfer coefficients were found in (Richardson, 2004) table 12.1. For a typical

vacuum condenser, the U value ranges between 200-500 W/m2 °C. Therefore the average will be

used:

U = 350W/m2 °C

Thus the area is calculated:

2417313.5350

10007740mA

Bare vessel cost (Figure 7.18) (A.M.Gerrard, 2000)

Purchased cost = £300,000

the cost in 2000 = £300,000, therefore price in 2010 = (137.6/100) ×300,000 = £412,800

Therefore total delivery cost of condenser in 2010 = £412,800

10.3.1.6 Pump

Power of pump is again obtained from ChemCAD, power = 28.2 kW

The type of pump being used is centrifugal pump

Total number of pumps = 1

From figure 7.34 (A.M.Gerrard, 2000) = £20,000 therefore price in 2010 =

(137.6/100) ×18,000 = £24,768

10.3.1.7 Thermal storage


123

Cost of storage in 2008 = 289 $/kW obtained from table5-13 (Group, 2003)

therefore cost index for 2008 = 575.4, for 2010 = 525.6

therefore cost in 2010 = 525.6/575.4*289 = 264 multiplying by power generatin in year =

264*3.15e6 = $8.32 million = 8.32/1.58 = $5.26 million

Total purchase cost of equipment items (PCE)

Estimation of fixed capital cost, reference Table 6.1 (Richardson, 2004), fluids processing plant:

PCE = £21,320,177

f1 Equipment erection 0.40

f2 Piping 0.70

f3 Instrumentation 0.20

f4 Electrical 0.10

f5 Buildings process 0.15

f6 Utilities 0.5

f7 Storages provided in PCE therefore N/A

f8 Site development N/A

f9 Ancillary buildings 0.15

Total physical plant cost = 16,060,177 × (1 + 0.4 + 0.7 + 0.2 + 0.1 + 0.15 + 0.5 + 0.15) =

£51,392,567

f10 Design and Engineering 0.30

f11 Contractor‟s Fee will be used 0.05

f12 Contingencies 0.10

Fixed capital cost = 51,392,567 × (1 + 0.3 + 0.05 + 0.1) =

£98,901,345


124

Levelised cost is calculated by finding the power output in one year =

Solar irradiance = 1154924.72 Wh/m2/year

Therefore power output =3.15eGWh/year

Thus levelised cost for lifespan of 25 years = 98,901,345 / (3.15e6×25) = £1.26 kWh

and levelised cost for lifespan of 30 years = 78,245,183 / (3.15e6×30) = £1.05 kWh


125

10.4 Short Term Storage

10.4.1 The Service life of PbA and other components in the system (50), (86)

N100 N80

N4

0

Temp

Correc

tion

Factor

t3,cyc

le at

DO

D

=10

0%

t3,cy

cle

at

DO

D

=8

0%

t3,cy

cle

at

DO

D

=4

0%

t3,fl

oat

Serv

ice

Life

DO

D

=10

0%

Serv

ice

Life

DO

D

=80

%

Servic

e Life

DOD=

40%

Act

ual

Serv

ice

life

Number

of

replace

ments

PbA

320-800

400-1000

1500 0.69 1.5 1.9 2.8 10 1.1 1.3 2.8 4.7 8

Ni

MH

300-

500

800-

1200

17

00 0.85 1.2 2.8 4.0 9 1.9 2.3 4.0 6.8 6

Ni-

Cd

300-

500

1000-

1500

20

00 0.9 1.2 3.7 4.9

22

.5 1.0 3.1 4.9 8.6 5

Li-

ion

3000-

5000

5000-

7000

75

00 0.72 9.9

10.

8

10.

8 15 7.9 10.8 10.8 21.6 2

Na

S

2300-

2500

4500-

5000

55

00 1 6.8

13.

7 15 15 6.6 13.0 15 28.7 1

Zn

Br

1500-

2500

2500-

3000

35

00 1 6.8 8.2 9 9 5.5 7.5 9 17.2 2

10.4.2 Annual capital costs for the solar chimney battery options (62), (63)

Annual Costs

Quantity

Stored/peak usage

Unit Price £ (BEST)

Unit Total Cost

£ Price £ (WORST)

Unit Total Cost £

Capital Cost

(CFC) (£)

PbA 7860 kWh £ 63 /kWh

£ 495,180 £ 79 £/kWh £ 620,940

Ni-Cd 8060 kWh £ 190 /kW

h £1,531,400 £ 379 £/kWh £ 3,054,740

NaS 7660 kWh £ 221 /kWh

£ 1,692,860

£ 316 £/kWh £ 2,420,560

Backup

Generator a

9000 kWh £

5,000 - £ 5,000 £ 5,000

£ 5,000

Inverter 650 /kW £ 981 £/kW

£ 637,650

£ 637,650

Air conditioner -

£ 284 - £ 284 £ 284

£ 284

TOTAL ANNUAL CAPITAL COSTS, CTC (Fixed Capital + Working Capital), inc 10%

contingency

PbA

£

1,246,425 £ 1,384,761

Ni-Cd

£

2,386,267 £ 4,061,,941

NaS

£

2,569,373 £ 3,369,843


126

10.4.3 Annual operating costs for the solar chimney batteries options (64)

DIRECT COSTS Percentage Total Cost £ (BEST) Total Cost £(WORST)

Maintenance (MTC) 2% of CFC £ 500 £ 500

Replacement

PbA 80% of CFC £ 396,144 £ 496,752

Ni-Cd

£ 1,225,120 £ 2,443,792

NaS

£ 1,354,288 £ 1,936,448

Total Direct Costs

PbA

£396,644 £497,252

Ni-Cd

£1,225,620 £2,444,292

NaS

£1,354,788 £1,936,948

TOTAL ANNUAL EXPENSES , inc 5% contingency

PbA

£416,476 £522,115

Ni-Cd

£1,286,901 £2,566,507

NaS

£1,422,527 £2,033,795

10.5 Seasonal Storage

10.5.1 Graph to show discharge hours for seasonal storage


127

10.5.2 Table to show calculation of seasonal storage capacity

Mo

nth

Ra

tio

ap

plie

d to

da

ta o

f

0.6

64197421

2 to

brin

g

into

line

with

de

sign

da

ta

So

lar

To

we

r

Ou

tpu

t

(kW

h)

So

lar C

him

Pro

du

ctio

n

(PV

GIS

figu

res)

(Wh

)

So

lar C

him

Pro

du

ctio

n

(HU

RN

figu

res)

(Wh

)

So

lar C

him

Pro

du

ctio

n

(PV

GIS

figu

res)

(kW

h)

So

lar C

him

Pro

du

ctio

n

(HU

RN

figu

res)

(kW

h)

So

lar P

V -a

-

si (kW

h)

Ch

an

ge

(Ch

imn

ey)

Disc

ha

rge

(kW

h)

Ch

arg

e

(kW

h)

Su

rplu

s

Ch

imn

ey

(kW

h)

Ch

an

ge

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we

r

(kW

h)

Disc

ha

rge

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we

r

(kW

h)

Ch

arg

e

(kW

h)

Su

rplu

s

To

we

r

(kW

h)

PV

Ch

an

ge

(kW

h)

Disc

ha

rge

PV

(kW

h)

Ch

arg

e

(kW

h)

Su

rplu

s PV

(kW

h)

Tro

ugh

Tro

ug

h

Ch

an

ge

(kW

h)

Disc

ha

rge

Tro

ug

h

(kW

h)

Ch

arg

e

(kW

h)

Su

rplu

s

Tro

ug

h

(kW

h)

Jan

uary

339003.4

885

74801.0

2527

81586283.7

493814911.3

281586.2

8374

93814.9

1132

72420

-245188.5

77

-245188.5

77

-264202.4

63

-264202.4

63

-266583.4

88

-266583.4

88

100,8

00.0

0-2

38203.4

88

-238203.4

88

Fe

bru

ary

301006.6

407

108817.0

567

144320324.5

151110488.7

144320.3

245

151110.4

887

108120

-149896.1

52

-149896.1

52

-192189.5

84

-192189.5

84

-192886.6

41

-192886.6

41

162,0

00.0

0-1

39006.6

41

-139006.6

41

Marc

h289578.9

068

272589.3

007

265330149.4

341884862.1

265330.1

494

341884.8

621

273020

52305.9

5536

52305.9

5536

-16989.6

061

-16989.6

061

-16558.9

068

-16558.9

068

366,0

00.0

076421.0

9325

76421.0

9325

Ap

ril240739.2

403

353769.6

289

428799562

443704170.9

428799.5

62

443704.1

709

358700

202964.9

307

202964.9

307

113030.3

886

113030.3

886

117960.7

597

117960.7

597

492,0

00.0

0251260.7

597

251260.7

597

May

231168.5

83

465494.4

674

515841716.8

583830321.9

515841.7

168

583830.3

219

477700

352661.7

389

352661.7

389

234325.8

844

234325.8

844

246531.4

17

246531.4

17

627,0

00.0

0395831.4

17

395831.4

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ne

217500.8

149

498725.6

861

568916201.4

625510913.1

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014

625510.9

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536180

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982

408010.0

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281224.8

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281224.8

712

318679.1

851

318679.1

851

693,0

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543

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781

335538.7

781

223565.6

109

223565.6

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452814339.5

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452814.3

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682

235455.2

682

143675.2

425

143675.2

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159700.9

287

159700.9

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486,0

00.0

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287

268640.9

287

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pte

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226573.6

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284408.0

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2911

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301

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61168700

Seasonal

Sto

rage

Require

ment

Can b

e s

old

at ra

te fo

r

chim

ney

outp

ut.

Seasonal

Sto

rage

Require

ment

Can b

e s

old

durin

g

sum

mer

month

s to

grid

Seasonal

Sto

rage

Require

ment

Can b

e s

old

to g

rid d

urin

g

the s

um

mer

Seasonal

Sto

rage

Require

ment

Can b

e s

old

to g

rid d

urin

g

the s

um

mer


128

10.5.3 Map of Ringmer and proposed seasonal storage location


Group 129

10.6 Suggested Project Gantt Chart

Large Scale Solar Generation - personal.ee.surrey.ac.uk

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