SOLAR CHIMNEY Solar Energy I Physics 471 2001-02-1 Instructor : Prof. Dr. AHMET ECEVIT Presented by : Yusuf SIMSEK.

SOLAR CHIMNEY

Solar Energy I

Physics 471

2001-02-1

Instructor : Prof. Dr. AHMET ECEVIT

Presented by: Yusuf SIMSEK

TABLE OF CONTENT PAGE

1. Introduction 4

2. The Collector 7

2. Structure of the Collector 8

3. Glazed Collector 9

4. The Energy Storage in the Collector 11

5. Chimney 13

6. Solar Chimney Prototype at Manzanares (Spain) 14

7. Turbines 16

8. How Does Collector Work? 17

9. Collector Efficiency 21

11. The Chimney 25

12. The Turbine 32

13. The Appropriate Charesteristic Curve 35

14. Typical Dymensions for Solar Chimneys 38

15. Termodynamics 39

16. Operation 41

17. Technical Data Quantities 42

18. Energy Production Costs 44

19. Conclusion 47

1.INTRODUCTION

Solar chimney converts the solar radiation into electricity. It consists of three simple parts:

–– Glass roof collector

–– Chimney

–– Turbine

Basically, air is heated by solar radiation under the glass roof and it starts to move toward to the chimney. Turbines which are placed at the base of the chimney converts this mechanical power into electricity (Fig. 1.).

“A single solar chimney with a suitable large glazed roof area and a high chimney can be designed to generate 100 to 200 MW continously 24 h a day. Thus even a small number of solar chimneys can replace a large nuclear power station. Solar chimneys operate simply and have a number of other advantages:

–– The collector can use all solar radiation, direct and diffused.

–– Due to the heat storage system the soalr chimney will operate 24h on pure solar energy.

–– Solar chimneys are particularly reliable and not liable to break down, in comparision with other solar generating plants.

–– Unlike conventional power stations (and also other solar thermal power station types), solar chimneys do not need cooling water.

–– Unlike conventional power stations (and also other solar thermal power station types), solar chimneys do not cooling water.

–– The building materials needed for solar chimney, mainly concrete and glass, are available everywhere in sufficient quantities.

–– Even in poor countries it is possible to build a large plant without high foreign currency expenditure by using their own resources and work forces [1].”

2. The Collector Collector is the part of the chimney that produce hot air by the green house effect. It has a roof made up of plastic film or glass plastic film. The roof material is stretched horizontally two or six meter above the ground. The height of the roof increases adjacent to the chimney base, so that the air is diverted to the chimney base with minimum friction loss. “This covering admits the short wave solar radiation component and retains long-wave radiation from the heated ground. Thus the ground under the roof heats up and

transfers its heat to the air flowing radially above it from the outside to the chimney [2].”

Collector

Chimney

Turbine

Fig. 1.Parts of the Solar Chimney

3. Structure of the Collector The structure of the collector changes to the covering material we used. If we use plastic film we can construct the skeleton by adjusting the space between the rods as 6 meter. In this type skeleton attaching plastic film is easy and it is particularly suitable for very large collector surface in remote places because of the small quantites of the materials needed and low transportation cost. “The 45 000 m2 of the prototype were covered with various plastic film and glass to establish the optimum and cheapest material in the long life term [3].”

4. Glazed Collector A flate glazed roof must have much more durable skeleton. Besause glazing increases the mass of the roof. Its rods are more stronger and they are attached like in the picture below (Fig. 2.). A collector roof of this kind has a very long life–span. “With proper maintanence this can easilly be 60 years or more [4].”

Fig. 2. Collector Glass Roof of Solar Chimney Prototype at Manzanares from Inside

“A flate glazed collector can convert up to 70% of irratiated solar energy into heat, dependent on air throughput, a typical annual average is 50%. Also the ground under the roof provides natural energy storage

at no cost [5].” Clearly, the temperature increases towards to the tower and energy loss increases near the chimney. We can increase the ability of the collector roof by double glazing about the tower (Fig. 3).

Fig. 3. Aerial View of Solar Chimney Prototype at Dusk.

5. The Energy Storage in the Collector “Water filled black tubes are laid down side by side on the black sheeted or sprayed soil under the glass roof collector (Fig. 4). They are filled with water once and remain closed thereafter, so that no evaporation can take place. The volume of water in the tubes is selected to correspond to a water layer with a depth of 5 to 20 cm depending on the desired power output. Since the heat transfer between black tubes and water is much larger than that between the black sheet and the soil, even at low water flow speed in the tubes, and since the heat capacity of water (4.2 kJ/kg) is much higher than that of soil (0.75 - 0.85 kJ/kg) the water inside the tubes stores a part of the solar heat and releases it during the night, when the air in the collector cools down [6].”

Fig. 4:Principle of heat storage underneath the roof using water-filled black tubes.

“The chimney is the plant’s actual thermal engine (Fig. 5). Its optimal surface-volume ratio decreases friction loss and makes it like a pressure tube. “The upthrust of the air heated in the collector is aproximately proportional to the air temperature rise ΔT in the collector and the volume of the cchimney. In a solar chimney the collector raises the temperature of the air by about ΔT= 35oC. This produce an updraught velocity in the chimney of about V=15m/s [7].”

6. Chimney

Fig. 5. Chimney

“The sheet metal was only 1.5mm thick

150m high

10m diameter

The debt of beading was 150mm

The sheets were abuted vertically at intervals of 8.6m and shiftened every 4m by exterior trussrirelers [8].”

7. Solar Chimney Prototype at Manzanares (Spain) (Fig. 6)

Fig. 6. Solar Chimney Prototype at Manzanares

Fig. 7. Prototype of the solar chimney at Manzanares.

chimney 195 m high

and 10 m in diameter

surrounded by a collector 240 m in diameter.

The turbines, the air current is converted into mechanical energy. The turbines are always placed at a height of 9 meter at the base of the chimney. According to the size of the turbine, they placed horizontally (Fig. 8) or verticaly (Fig. 9) and also the number of the turbines can vary.

8.Turbines

Fig. 8. Horizontal Fig. 9. Vertical

When solar radiation pass through the transparent roof it is absorbed by the ground elements and it converts into heat energy. When air is heated it starts to rise up and, starts to move toward the chimney and gains a velocity (Fig. 10).

9.How Does A Collector Work?

“A solar chimney collector converts available solar radiation G onto the collector surface Acoll into heat output.

Collector efficiency ncoll can be expressed as ratio of the

heatoutput of the collector as heated air Q and the solar radiation G (measured in W/m2) times Acoll[9].”

Fig. 10. Solar Chimney Power Plants

Collector Efficiency Heat Output

Collector Area Solar Radiation

Mass flow

Spesific heat capacity of the air

The temperature differences between the collector and out flow

Air speed at collector outflow/chimney inflow Chimney cross-section area

Spesific dendsity of air at temperature To + ΔT at collector outflow/chimney inflow

10. Collector Efficiency

Additionaly valid for heat balance collector:

Effective absorption coefficient of the collector

Loss correction value (in W/m2K), allowing for emission and convection loss

Thus collector efficiency can also be expressed like this:

In order to find velocity

These equations are independent of roof height because friction loses and ground storage in the collector area neglected.

= 0.75-0.8

= 5-6 W/m2

G=1000 W/m2

ΔT=300C

Typical Values:

=% 62

11.The Chimney

“The efficiency of the chimney (i.e. The conversion of heat into kinetic energy) is particularly independent of the rise of air temperature in the collector; it is essentially determined by the outside temperature To at ground level (the lower the better). Thus solar chimneys can make particularly good use of the low rise in air temperature produced by heat emitted by the ground during the night and even the meager solar radiation of a cold day. Comparing with the collector and turbine, the chimney efficiency is relativelly low, hence the importance of size in its efficiency curve. For example, at a height of 1000 meters, chimney efficiency is somewhat greater than 3% [10].”

HC

Outher air is cold relative to the air inside the chimney

Pressure in outher enviroment is different from the inside the

chimney.

P(pressure) under the gravity changes with respect to h

in differatial form

And

g : acceleration due to gravity

HC : Chimney height

: density

Fig. 11 Chimney Height

T0

Out of the chimney

Inside of the chimney

Air density in outer environment

Air density in the chimney

HC

Fig. 11 Chimney Height

Thus ΔPtot increases with chimney height.

ΔPtot is consist of two components

The static pressure difference drops at the turbine, the dynamic component describes the kinetic energy of the air flow.

(dynamic and static)

so

Ptot= ΔptotVC,max AC Efficiency of the chimney can be established

ΔPS= O ΔPtot=ΔPd

ΔPtot =ΔPS+ΔPd

Power volume

Actual division of the pressure difference into a static and a dynamic component depends on the energy taken up by the turbine. If the turbine is left out, a maximum flow speed of VC,max is achieved and the whole pressure difference is used to accelerate the air.

Toricelli Equation:

T0 ambient temperature at ground level

ΔT Temperature rises between collector inflow and collector outflow /chimney inflow

This basic simplified explanation one of the basic charesteristic of the solar chimney,which is that the chimney efficiency is fundamentaly dependent only on chimney height. Flow speed and temperature rise in the collector do not come into it.

Thus the power contained in the flow

12.The Turbine “Turbine in a solar chimney do not work with staged velocity like a free-running wind energy converter, but as a closed pressure-staged wind turbogenerator, in which, similarly to a hydroelectric power station, static pressure is converted to rotational energy using a cased turbine- in this aplication installed in a pipe. The energy yield of a cased pressure-staged turbine of this kind is about eight times greater than that of a speed-stepped open-air turbine of the same diameter.

Air speed before and after the turbine is about the same. The output achieved is proportional to the product of volume flow per unit time and the fall in pressure at the turbine. With a view to maximum energy yield the aim of the turbine regulation system is to maximize this product under all operating conditions [11].”

Blade pitch is adjusted during operation to regulate power output according to the altering air speed and air flow (Fig. 11). As soon as the wind speed in the chimney exceed 2.5 m/s the turbine is started automaticaly and cut into the public grid. The output power of the turbine is adjusted by limiting the rotation frequency of the turbine. This can be adjusted by changing the blade angle automatically (Fig. 12).

Fig. 11. Turbine Propeller Fig. 12. Blade Angle

The pressure drop

Theoretical useful power Powerwt at turbine

Powerwt =VC AC ΔPS

Electrical Power W = V I

Volume Flow

And finally we get the equation

13. The Appropriate Charesteristic Curve

2/3 ΔPtot

ΔPtot

ΔPs

P=VΔPS

.O

.V

Powerwt takes a minimum between these extreme at:

Fig. 13. Characteristic Curve

Thus mechanical power taken up by the turbine is:

Powerwt,max = (2/3)ncoll nc Acoll G

Powerwt,max = (2/3)ncoll(g/CpTo)HoAcollG

Chimney Height HC: –––––––– 750m

Collector Diameter Dcoll: –––––––– 2200m

Solar Irradiation G: –––––––– 1000W/m2

Mechanical Efficiency nwt : –––––––– 0.8

Collector Efficiency ncoll : –––––––– 0.6

Heat Capacity of the Air CP : –––––––– 1005j/kgK

Ambient Temperature T0 : –––––––– 200C

Gravity Acceleration g : –––––––– 9.81m/s2

Pelectric: (2/3)(0.8x0.6)[9.81/(1005x293)]x750x3751000x1000

Pelectric: 30 MW

14. Typical Dymensions for Solar Chimneys With Different Power

Power Block Size

MW 5 30 100 200

Collector Diameter Dcoll

m 1110 2200 3600 4000

Chimney Height HC

m 445 750 950 1500

Chimney Diameter DC

m 54 84 115 175

Annual Energy Production

GWh/y 13.9 87.4 305.2 600

With 2300 kWh/m2y global radiationDymensions

Table. 1: Typical Dymensions for Solar Chimneys With Different Power

15. Thermodynamics

Power Block Size MW 5 30 100

Temperature rise in Collector

oK 25.6 31.0 35.7

Updraft Velocity in Chimney

(ful load) m/s 9.1 12.6 15.8

Total Pressure Difference

Pa 388.3 767.1 1100.5

Pressure Loss by Friction

(Collector And Chimney)

Pa28.6 62.9 80.6

Pressure Drop at turbine

Pa314.3 629.1 902.4

With 2300 kWh/m2y global radiation

Table. 2: Thermodynamics Data

Pressure Loss at Chimney Top

Pa 40.4 75.1

Average Annual Efficiency

Collector % 56.24% 54.72%

Chimney % 1.45% 2.33%

Turbines % 77.00% 78.30%

Whole System % 0.63% 1.00%

117.5

52.65%

3.10%

80.10%

1.31%

Table. 2: Thermodynamics Data

Power Block Size MW 5 30 100

Annual Energy Production

Total GWh/y 13.9 87.4 305.2

Per m2 kWh/m2y 14.4 23.0 30.0

Annual Operating Hours

h/y 8423 8506 8723

Full Load Hours h/y 2780 2913 3052

Capacity Factor % 31.7% 33.3% 34.8%

Night Energy Production

GWh/y 1.5 8.7 32.0

16. Operation

Table. 3: Operation Data

Power Block Size MW 5 30 100

Collector Diameter m 1110 2200 3600

Glass Collector Roof-interior Diameter

m 162 252 346

Total Covered Area m 76 118 159

Glass Roof Area

Totalm2 967700 3801000 10180000

Double Glazed

2x4mmm2 328880 1318000 3570000

Single Glazed

1x4mm m2 61900 2433000 6510000

17. Technical Data Quantities

Table. 4: Collector Data Quantities

Glass Roof Area m2 947700 3801000 10080000

Chimney Area m2 4500 11000 20000

Glass Roof Height

(external)m 2.0 4.5 6.5

Glass Roof Height

(internal )m 10.0 15.5 20.5

Total Quantity 4mm Raw Glass

km2 1.3 5.1 13.7

Table. 4: Collector Data Quantities

18. Energy Production Costs “With the support of construction companies, the glass industry and turbine manufacturers a rather exact cost estimate for a 200 MW solar chimney could be compiled. We asked a big utility "Energie in Baden-Württemberg" to determine the energy production costs compared to coal- and combined cycle power plants based on equal and common methods (Table. 5) [12].

Table. 5: Comparison between the energy production costs of a 2 x 200 MW solar chimneys and 400 MW coal and combined cycle power plants according to the

present business managerial calculations.

Fig. 14. Energy production costs from solar chimneys, coal and combined cycle power plants depending on the interest rate.

CONCLUSION “No ecological harm and no consumption of resources, not even for the construction. Solar chimneys predominantly consist of concrete and glass which are made from sand and stone plus self-generated energy. Consequently in desert areas - with inexhaustible sand and stone solar chimneys can reproduce themselves. A truly sustainable source of energy! [13].”

REFERENCES:

1. The Solar Chimney. The use of three “old“ technologies. Retrieved 1 December 2001 from; http://wire0.ises.org/wire/Publications/Research.nsf/defaultview/0DED34BF3EB9A985C12569840055F09E/$File/SolarChimney_short_version.pdf

2. Schlaich, J. (1995). Solar Chimney: Electricity from the Sun. Stuttgart; Edition Axel Menges, p.16.

3. Schlaich, J. (1995). Solar Chimney: Electricity from the Sun. Stuttgart; Edition Axel Menges, p.28.

4. Schlaich, J. (1995). Solar Chimney: Electricity from the Sun. Stuttgart; Edition Axel Menges, p.17.

5. Schlaich, J. (1995). Solar Chimney: Electricity from the Sun. Stuttgart; Edition Axel Menges, p.16.

6. The Solar Chimney. The energy storage. Retrieved 1 December 2001 from; http://wire0.ises.org/wire/Publications/Research.nsf/defaultview/0DED34BF3EB9A985C12569840055F09E/$File/SolarChimney_short_version.pdf

7. Schlaich, J. (1995). Solar Chimney: Electricity from the Sun. Stuttgart; Edition Axel Menges, p.18.

8. Internet sayfasini bul

9. Schlaich, J. (1995). Solar Chimney: Electricity from the Sun. Stuttgart; Edition Axel Menges, p.52.

10. Schlaich, J. (1995). Solar Chimney: Electricity from the Sun. Stuttgart; Edition Axel Menges, p.18.

11. Schlaich, J. (1995). Solar Chimney: Electricity from the Sun. Stuttgart; Edition Axel Menges, p.20.

12. The Solar Chimney. Energy Production Costs. Retrieved 1 December 2001 from; http://wire0.ises.org/wire/Publications/Research.nsf/defaultview/0DED34BF3EB9A985C12569840055F09E/$File/SolarChimney_short_version.pdf

13. The Solar Chimney. Energy Production Costs. Retrieved 1 December 2001 from; http://wire0.ises.org/wire/Publications/Research.nsf/defaultview/0DED34BF3EB9A985C12569840055F09E/$File/SolarChimney_short_version.pdf

Fig. 2. Collector glass roof of solar chimney prototype at Manzanares from inside. Retrieved 30 November 2001 from;

http://wire0.ises.org/wire/independents/imagelibrary.nsf/25bcb7328e30a3e 2c12567530049c67f/A892385128ECAD96C12569840050A66F/$File/glass_roof_from_inside.jpg

Fig. 3. Aerial View of Solar Chimney Prototype at Dusk. Retrieved

30 November 2001 from; http://wire0.ises.org/wire/independents/ImageLibrary.nsf/H/O?Open&840A07E8A8A6A557C1256984004EEDF8

Fig. 4. The energy storage; Principle of heat storage underneath the roof using water-filled black tubes. Retrieved 1 December 2001 from; http://wire0.ises.org/wire/Publications/Research.

nsf/defaultview/0DED34BF3EB9A985C12569840055F09E /$File/SolarChimney_short_version.pdf

Fig. 5. Solar Chimney prototype during construction. Retrieved 30 November 2001 from; http://wire0.ises.org/wire/independents/imagelibrary.nsf/396e92819880db7dc125680f00443688/1982AF4545393096C1256984004F7395/$File/SolarChimneyManzanaresChimneyConstruction.jpg

Fig. 6. Solar Chimney Prototype at Manzanares. Retrieved 30 November 2001 from; http://wire0.ises.org/wire/independents/imagelibrary.nsf/396e92819880db7dc125680f00443688/1162284EE820787FC1256984004CF03F/$File/manzanares_air.jpg

Fig. 10. Solar Chimney Power Plants. Retrieved 30 November 2001 from; http://www.argonet.co.uk/users/bobsier/sola6.html

Fig. 14. The Solar Chimney. Energy Production Costs. Retrieved 1 December 2001 from; http://wire0.ises.org/wire/Publications/Research.nsf/defaultview/0DED34BF3EB9A985C12569840055F09E/$File/SolarChimney_short_version.pdf

Table. 1: Schlaich, J. (1995). Solar Chimney: Electricity from

the Sun. Stuttgart; Edition Axel Menges, p.36.

Table. 2: Schlaich, J. (1995). Solar Chimney: Electricity from,

the Sun. Stuttgart; Edition Axel Menges, p.37.

Table. 3: Schlaich, J. (1995). Solar Chimney: Electricity from

the Sun. Stuttgart; Edition Axel Menges, p.37.

Table. 4: Schlaich, J. (1995). Solar Chimney: Electricity from

the Sun. Stuttgart; Edition Axel Menges, p.38.

Table. 5: The Solar Chimney. Energy Production Costs.

Retrieved 1 December 2001 from; http://wire0.ises.org/wire/Publications/Research.nsf/defaultview/0DED34BF3EB9A985C12569840055F09E/$File/SolarChimney_short_version.pdf