Viability of Micro Wind Turbines in the Urban Environment · PDF fileWECS (including micro wind turbines) include: – Initial cost per kW generated – Maintenance costs ... –...

Ghanim Putrus

Reader in Electrical Power Engineering

Power and Wind Energy Research (PaWER) group

School of Computing, Engineering and Information Sciences

Northumbria University

Newcastle upon Tyne NE16 5RD, UK

E-mail: [email protected]

Mahinsasa Narayana

Keith Sunderland Dublin Institute of Technology, Ireland

Michael Conlon Dublin Institute of Technology, Ireland

Viability of Micro Wind Turbines in the

Urban Environment

World Renewable Energy Forum WREF/WREN

May 13-17, 2012, Denver, Colorado

Presentation Outline

• Introduction and Background

• Energy Conversion in Micro Wind Turbines

• Siting of Wind Turbines

• Sensitivity Analysis

• Results

• Optimal System Configuration

• Conclusions

Viability of Micro Wind Turbines in the

Urban Environment

Introduction

• A growing economy means a growing demand for electrical energy.

• The Kyoto Protocol Targets

– Developed countries to reduce greenhouse gas emissions by ~ 5% of

1990 levels in the period 2008-2012.

• The 20/20/20 energy targets for European countries; By 2020:

– 20% reduced CO2 emission

– 20% lowered energy consumption

– 20% more renewable energy in the system

• The UK Energy Policy

– 80% reduction of greenhouse gas emissions below 1990 levels by 2050

– 31% UK Electricity from renewables by 2020 (currently, this is ~6%)

• This will require: ~ 10 GW of Renewables

– 10 GWe of Combined Heat and Power (CHP) capacity by 2010!

• This will require hundreds of large CHP and numerous CHP installations.

The UK Electricity Generation Mix and Challenges

• Main Challenges to Renewable

Energy:

– Ambitious targets

– Cost

– Reliability and safety

– Technical problems

• Connection to the grid

• Voltage and frequency control

– Public acceptance

2020

2009

Wind Energy Conversion Systems

• Wind energy conversion systems (WECS) are currently

the most fast growing commercial resources of

renewable energy.

• Factors that largely affect the economic viability of

WECS (including micro wind turbines) include:

– Initial cost per kW generated

– Maintenance costs

– Potential energy generated

• Average wind speed

• Turbine type, size, mechanical design, etc.

• Maximum power point tracker (MPPT)

– The actual value of 1 kWh of electricity produced, which

depends on the fuel price, load profile and electricity tariff.

Growth of Renewable Generation Capacity in

the UK

2010 2020

RO : Renewables Obligation

Genera

tion a

s a

perc

enta

ge o

f sale

s

Source: Ofgem Sustainable Development Report, November 2007

• Micro generation can help meeting the targets for renewable energy.

• Micro generation (including micro wind generation) is still at early stages

of market penetration.

Micro Wind Turbines

• Current trends show a growing market for micro wind

systems.

• In the rural environment, the average wind speed is relatively

high and the wind speed/direction is reasonably stable.

• In the urban environment, the average wind speed tends to

be low and wind direction is constantly changing (turbulent

wind).

• Performance of the wind turbines in the urban environment is

very sensitive to the location and is generally poor.

• Most micro WTs do not perform as expected and operate

without adequate MPP tracking.

• Micro wind systems are generally expensive (over £2,500

per kW installed) and payback time (particularly for the urban

environment) currently is unrealistically long.

Micro Wind Turbines

• Available studies on the performance of micro wind

turbines in the urban environment are generic, e.g. that

technology can work if installed correctly and in appropriate

locations!

• There is a need to establish the various factors that affect

performance of small scale wind turbines, particularly in the

urban environment, and find out minimum requirements to

make such installations commercially viable.

Main Components of Micro Wind Turbine

Wind Power

PWind

Aerodynamic

power

extracted by

the wind rotor

PMG

Ploss = IG2 + Friction losses

Aerodynamic

losses

Rectifier

Inverter

Pwind – PLosses

Power Electronic converter losses

MPPT

A.C. power

generated

Micro wind turbines can be:

Horizontal axis (HAWT)

Vertical axis (VAWT).

Wind Energy Conversion

3...2

1 vAρCP

pa

v

R.

Where

is the air density

A is the turbine swept area = R2

(R is the radius of the rotor)

v is the wind speed

Cp is the power coefficient which depends on the pitch angle of

the wind rotor blades and on the tip speed ratio () defined as:

The captured power by the wind rotor

depends on the wind speed and wind

turbine aerodynamic characteristics.

According to Betz’s law, the aerodynamic

power extracted by the wind rotor is:

is the rotational speed of the rotor

V1

V2

V3

V4

Maximum

aerodynamic

power points of

the wind rotor

Rotational speed

Po

we

r

Wind rotor

curves at

different wind

speeds

Operating Points of Wind Turbine Rotor

• At steady state, wind turbine generator systems are operated at the points

where the wind rotor curve and the electrical generator curve coincide. These

points may not represent the optimal condition of the system.

• When the wind speed varies, the rotor speed should be adjusted to follow the

optimum operating point for maximum power generation. However, changing

the rotor speed to follow the variation of wind speed is particularly difficult in

turbulent wind conditions.

V1

V2

V3

V4

Restoring power

curve of the

generator

Maximum

aerodynamic power

points of the wind

rotor

Rotational speed

Po

wer

Wind speeds

Wind rotor curve

(Fixed pitched wind

turbine)

Operating

points Wind rotor

PMG

Wind Energy Conversion

• The coefficient Cp has a maximum value at a certain value of which

results in a maximum possible (theoretical) power extraction of ~60%.

• MPP tracking in turbulent wind conditions is very difficult (not effective) due

to the inertia of the wind turbine .

• This, in addition to losses due to blade roughness, hub, tip, generator and

inverter losses result in a reduction of the overall energy conversion to

around 30%.

Mechanical

Power

Aerodynamic

losses

(55%)

Electrical

Power output

(30%)

Electric

generator

losses

(10%)

Converter

losses

(5%)

Wind power

(100%)

Electrical Power

Siting of Small Wind Turbine

• In most of the places in the UK, the wind speed is

more than 5 m/s at 25 m height.

• Siting of wind turbines is very important to achieve

accepted performance. Location; Location; Location!

• The BERR developed Numerical Objective Analysis

of Boundary Layer (NOABL) Wind Speed Database

ultilises an air flow model that estimates the effect of

topography on wind speed. This model is limited by

the fact that there is no allowance for the effect of

local thermally driven winds and also by virtue that it

has a 1 km2 resolution (at either 10 m, 25 m or 45 m

above ground level) in which there is no

consideration of small scale topography.

• In more constricted (urban) areas, wind speeds will

be lower and wind resource estimation, particularly

at lower elevations, is very challenging.

Annual mean wind speed

Sensitivity Analysis

• Cost of energy and initial cost of the system are the most important

parameters to evaluate economic viability of small wind power systems.

• Cost Of Energy (COE) is the average cost per 1 kWh (£/kWh) of useful

electrical energy produced by the system and may be described as:

Where;

– Cann,tot = Total average annual cost of the system (£/Year),

– Eprim = Primary load served (kWh/Year),

– Edef = Deferrable load served (kWh/Year),

– Egrid,sales = Total grid sales (kWh/Year)

• Estimated cost of a typical small system is £2,500 - £5,000 per kW

capacity installed, though this may go down to less than £1,000 with mass

production.

• The maintenance costs are between 1.5% and 3% of the turbine cost but

increase with time as the turbines get older.

salesgriddefprim

totann

EEE

CCOE

,

,

Sensitivity Analysis

• The average annual capital cost (Cann,cap) of the system may be represented as:

Where

– Ccap = Initial capital cost (£)

– CRF(i, N) = Capital recovery factor defined as:

– i = Annual interest rate

– N = Project lifetime measured in number of years

• System considered:

– 2.4 kW micro wind turbine system (Skystream 3.7).

– Initial cost of the system = £9500

– Annual operation and maintenance cost = £250.

– Life time of the system = 25 years

– Replacement cost is considered equal to initial cost of the system (salvage cost is neglected).

– The annual interest rate = 6%.

– Annual energy production is determined based on power curves provided by the manufacturer.

),(., NiCRFCC capcapann

1)1(

)1(),(

N

N

i

iiNiCRF

Power Flow and Load Profiles

Typical daily load profile for a

domestic load

Based on ADMD referenced to a

nominal 100 consumers and measured

at a distribution substation on an

outgoing feeder

Household

consumer Grid sales and

purchases

Electricity

demand

2.4 kW micro wind

turbine system

(Skystream 3.7)

Grid

Generation

Main

Distribution

Board

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Time (hr)

Po

wer

dem

an

d (

kW

)

Summer

Autumn and spring

Winter

Typical Energy Production

• A typical wind pattern in UK was considered (hourly wind data based on 5 m/s annual

mean wind speed).

• Grid sales and purchases were calculated by considering hourly based energy

generation of the wind turbine and typical domestic demand throughout the year.

Monthly mean wind speed, energy production and grid sales

for 5 m/s annual mean wind speed

801

676

719

451

312

216

179 179

331

530

607

718

371

310

436

219

11297

69 71

130

279

340317

0

100

200

300

400

500

600

700

800

900

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

En

erg

y (

kW

h)

0

1

2

3

4

5

6

7

Win

d s

pee

d (

m/s

)

Energy production by the wind turbine(kWh)

Grid sales (kWh)

Monthly mean wind speed (m/s)

Results of Sensitivity Analysis

• “HOMER” micro power optimisation model (developed by

National Renewable Energy Laboratory, USA) was used to

calculate cost of energy for various initial cost values and

different annual mean speeds.

• Annual energy productions by the wind turbine (SW-

Skysream3.7) and cost of energy production based on different

initial cost values for different annual mean speeds were

determined.

Annual Energy Productions and Cost of Energy

Production by the Wind Turbine per kWh

2.4 kW micro wind turbine system (SW-Skystream3.7)

Annual mean wind speed

3m/s 4m/s 5m/s 6m/s 7m/s 8m/s 9m/s

Init

ial c

os

t p

er

1k

W

ins

talla

tio

n

£7,917 £1.29 £0.57 £0.35 £0.25 £0.20 £0.17 £0.16

£7,125 £1.16 £0.52 £0.31 £0.23 £0.18 £0.16 £0.14

£6,333 £1.03 £0.46 £0.28 £0.20 £0.16 £0.14 £0.13

£5,542 £0.90 £0.40 £0.24 £0.18 £0.14 £0.12 £0.11

£4,750 £0.77 £0.34 £0.21 £0.15 £0.12 £0.10 £0.10

£3,958 £0.64 £0.29 £0.17 £0.13 £0.10 £0.09 £0.08

£3,167 £0.52 £0.23 £0.14 £0.10 £0.08 £0.07 £0.06

£2,375 £0.39 £0.17 £0.10 £0.08 £0.06 £0.05 £0.05

£1,583 £0.26 £0.12 £0.07 £0.05 £0.04 £0.04 £0.03

£792 £0.13 £0.06 £0.04 £0.03 £0.02 £0.02 £0.02

AEP (kWh) 1542 3462 5717 7921 9856 11406 12545

Assuming current electricity buying price of ~0.15 £/kWh, a minimum average wind

speed of 5 m/s is needed to make the wind turbine a cost effective source of electricity

based on current prices and technology used.

This agrees with the recommendation of the Energy saving Trust, UK.

Optimal System Configuration

• Optimal system configuration to supply domestic demand is analysed by considering

energy cost for grid supply only or grid in addition to an integrated wind turbine.

• Energy cost of grid supply integrated with wind turbine depends on time based energy

demand, energy generation by wind turbine, electricity Feed In Tariff and buying price.

• HOMER was used to determine optimal system configuration for different initial cost and

various annual mean speeds.

• A grid-connected wind turbine would be cost effective within the area shaded in green.

The cost of electricity generation per kWh for a micro grid-connected wind turbine

Viable Initial Cost of Micro Wind Turbines

Annual mean wind

speed

Viable maximum initial cost

per 1 kW capacity installed

3 m/s < £950 / kW

4m/s < £2280 / kW

5m/s < £3800 / kW

6m/s < £5700 / kW

7m/s < £7410 / kW

• For micro wind turbines to be viable in the urban environment,

need to:

• Reduce the initial cost of the system (to less than £1000/kW

capacity installed). Operation cost is comparatively low.

• Improve the wind turbine aerodynamics and energy capture at

low wind speed

• Reduce power losses in the generator and power electronic

converter.

• Have generous Feed In Tariffs (FIT) for the foreseeable future.

Conclusions

• An important component which affects the performance of the

wind turbine system is the maximum power point tracker (MPPT).

• The turbulent nature of wind in the urban environment and the

inertia of the wind turbine make it practically impossible to track

the wind speed/direction and operate close to the maximum

power point, particularly for HAWTs.

• It is important to consider the use of advanced dynamic

maximum power point tracking control techniques, e.g. wind

speed forecasting, predictive control, active yaw control, etc. to

maximize energy capture when operating in turbulent wind

conditions.

Conclusions

Predictive Control by Considering Wind Speed

Forecasting Techniques

0

1

2

3

4

5

6

7

0 200 400 600 800 1000 1200 1400Time (sec)

Win

d s

pee

d (

m/s

)

measured

Prediction_NN

• Wind speed-time series data typically exhibit autocorrelation, which can

be defined as the degree of dependence on preceding values.

• Time series prediction takes an existing series of data and forecasts

future values.

MPPT Performance with and without Wind

Prediction

Wind rotor

Radius of wind rotor : 1.105m

Blade profile : NACA4415

Number of blades : 2

Moment of inertia (J) : 9.77kg.m2

0

5

10

15

20

25

30

35

40

45

0 200 400 600 800 1000 1200 1400Time (s)

Ro

tatio

na

l sp

ee

d (

rad

/s)

Optimum

Actual with prediction

Actual without prediction

• Performance of the predictive MPPT control was compared with

conventional MPPT control system, which operates without prediction .

• The results obtained show that predictive control system improves the

response time of the MPPT controller and performs well in turbulent wind

condition.

Energy Extraction in 1350 Sec

With prediction Without prediction

Available energy 44.0218kJ 44.0218kJ

Extracted energy 34.9705kJ 32.9018kJ

Actual energy

extraction %

79.43% 74.73%

Thank You

Viability of Micro Wind Turbines in the

Urban Environment

Ghanim Putrus

School of Computing, Engineering and Information Sciences

Northumbria University

Newcastle upon Tyne NE16 5RD, UK

E-mail: [email protected]