THE SOLAR CHIMNEYTHE SOLAR CHIMNEYSolar Energy I

Physics 471

2002-03-1

By

Elif YURDANUR

Sırma ŞEN

Instructor: Prof.Dr.Ahmet ECEVİT

Dept. of Physics, M.E.T.U., Ankara.

1.1. Introduction.................................................…Introduction.................................................…….…. 11

22. . The Solar Chimney.....................................…The Solar Chimney.....................................…….…. 22 2.1. The Collector.........................................2.1. The Collector.........................................…………..……..

44

2.1.1. Construction of the Collector ........…2.1.1. Construction of the Collector ........… 77 2.2. 2.2. The Turbines...................................The Turbines...................................…………………………

99

2.2.1. Construction of the Turbines...…2.2.1. Construction of the Turbines...……..….. 1212 2.2. 3.3. The Chimney .......................The Chimney .......................…………………………….…………….

1414

2.3.1. Construction of the Chimney...…2.3.1. Construction of the Chimney...……… 1717

3.3. Cost................................................…Cost................................................……………..………….. 2020

44. . Conclusion ........................................…Conclusion ........................................…………..……….. 2424

References .......................................…References .......................................…………..……….. 2626

Table of Contents Table of Contents Page

1. Introduction1. Introduction It is well-known that the energy It is well-known that the energy

sources we have are either limited, sources we have are either limited, hazardous or dangerous. The solar energy, hazardous or dangerous. The solar energy, however, is continuous and ecologically however, is continuous and ecologically friendly (nonpolluting) [1]. It has started to friendly (nonpolluting) [1]. It has started to play an important role in our lives.play an important role in our lives.

There are many ways of using the There are many ways of using the solar energy. One of them is solar energy. One of them is the solar the solar chimneychimney, , which canwhich can convert the solar convert the solar energy into electrical energy directly. A energy into electrical energy directly. A solar chimney is as shown in Figure 1.solar chimney is as shown in Figure 1.

-1--1-

Fig.1Fig.1 The Solar Chimney in Manzanares The Solar Chimney in Manzanares

[2].[2].-2--2-

The solar chimney is composed of three main parts:

The CollectorThe cover

which helpsthe air to

be heated.

The TurbinesThe device

through whichthe warmed air passes in order

to generateelectrical energy.

The ChimneyThe pipe where the hot air from the turbines

rises up.

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2.1. The Collector2.1. The Collector

The collector is a The collector is a cover in which the air is cover in which the air is heated. The coverheated. The cover is is approximatelyapproximately 5 meters 5 meters high and has no sides, high and has no sides, it has only horizontalit has only horizontal top covering as shown top covering as shown in Figure 2.in Figure 2.

-4--4-

Fig.2Fig.2 The Collector [2]. The Collector [2].

Fig.3 A ViewFig.3 A View from the Inside of a Collector [2]. from the Inside of a Collector [2].

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As seen in Figure 3, the inside of a collector is about 5 meters high.

The air below this cover is heated by The air below this cover is heated by means of means of greenhouse effect.greenhouse effect. For this For this process, the collector should be made up process, the collector should be made up of a transparent material such as glass or of a transparent material such as glass or plastic film so that the solar radiation can plastic film so that the solar radiation can enter inside. The covering admits the enter inside. The covering admits the short-wave radiation component. However short-wave radiation component. However it retains long-wave radiation from the it retains long-wave radiation from the heated ground, and transfers its heat to heated ground, and transfers its heat to the air flowing above it to the chimney [2]. the air flowing above it to the chimney [2].

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2.1.1. Construction of the 2.1.1. Construction of the CollectorCollector

SizeSize: : The height of the collector is The height of the collector is ideally between 2 and 6 meters [2].ideally between 2 and 6 meters [2].

There is no limitation for the area of There is no limitation for the area of the collector. If we have larger area, we the collector. If we have larger area, we can generate more energy. For example, can generate more energy. For example, for a 10MW energy output, 2.5x10for a 10MW energy output, 2.5x105 5 mm2 2 area area is required [3].is required [3].

The height of a collector should The height of a collector should slightly increase towards the conjunction slightly increase towards the conjunction with the chimney so that the air is diverted with the chimney so that the air is diverted to vertical movement with minimum friction to vertical movement with minimum friction loss.loss. -7--7-

Life SpanLife Span: : It is determined by its It is determined by its resistance to dust and sand. With proper resistance to dust and sand. With proper maintenance, its life span can easily be 60 maintenance, its life span can easily be 60 years or more [2]. years or more [2].

In addition, the collector can be more In addition, the collector can be more efficient by double-glazing the parts near efficient by double-glazing the parts near the tower. In this way the collector can the tower. In this way the collector can retain heat more successfully as the air retain heat more successfully as the air temperature increases from the perimeter temperature increases from the perimeter towards the tower. towards the tower.

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2.2. The Turbines2.2. The Turbines

Turbine is a device Turbine is a device in which the electrical in which the electrical energy is derived. The air energy is derived. The air warmed in the collector warmed in the collector rises up towards the rises up towards the chimney and runs the chimney and runs the turbine. This results in turbine. This results in rotational energy in the rotational energy in the turbine. This can be seen turbine. This can be seen in the Figure 4.in the Figure 4.

-9--9-

Fig.4 Heated Air Rises Up [4].

This rotational energy is converted This rotational energy is converted into electrical energy. For this process one into electrical energy. For this process one turbine whose blades cover the whole turbine whose blades cover the whole cross-section of the chimney or many cross-section of the chimney or many smaller turbines distributed around the smaller turbines distributed around the circumference of the chimney wall can be circumference of the chimney wall can be used [2].used [2].

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For both choices, turbines should always For both choices, turbines should always be placed at the base of the chimneybe placed at the base of the chimney as seen as seen iin n the the

Figures 5 and 6.Figures 5 and 6. -11--11-

Fig.5Fig.5 A Single Turbine [2] A Single Turbine [2].. Fig.6 Small Turbines [2]Fig.6 Small Turbines [2]..

2.2.1. Construction of the Turbines2.2.1. Construction of the Turbines

SizeSize:: Either a large number of small Either a large number of small turbines with horizontal axes may be turbines with horizontal axes may be arranged around the base of the chimney, arranged around the base of the chimney, or one large, say a 100 MW turbine with a or one large, say a 100 MW turbine with a vertical axis is placed in the chimney’s vertical axis is placed in the chimney’s cross-section [5].cross-section [5].

If small turbines are to be chosen, for If small turbines are to be chosen, for instance 6 small turbines, they must be instance 6 small turbines, they must be selected in such a way that the blade selected in such a way that the blade lenght of each turbine will be a sixth of the lenght of each turbine will be a sixth of the chimney diameter.chimney diameter.

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Life SpanLife Span:: The turbine’s life span is The turbine’s life span is based on its resistance to rapid pressure based on its resistance to rapid pressure and speed changes of the air [2].and speed changes of the air [2].

Moreover, if smaller turbines are Moreover, if smaller turbines are used instead of a single large turbine, the used instead of a single large turbine, the overall cost will be lower [5].overall cost will be lower [5].

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2.3. The Chimney2.3. The Chimney

The main The main body of the plant body of the plant which the warmed which the warmed air flows through air flows through can be seen in the can be seen in the Figure 7. Figure 7.

-14--14-Fig.7Fig.7 The Chimney [2]The Chimney [2]..

In collector, the air temperature rises In collector, the air temperature rises up and therefore air gains a velocity to go up and therefore air gains a velocity to go upward in the chimney. However this upward in the chimney. However this amount of temperature rise is partically amount of temperature rise is partically independent of the efficiency of the independent of the efficiency of the chimney. This efficiency (n) is determined chimney. This efficiency (n) is determined by the outside temperature (Tby the outside temperature (T00) and the ) and the

height of the chimney (Hheight of the chimney (Hcc); which can be ); which can be

seen by the relation:seen by the relation:

n n ~~ H Hc c / T/ T00 (eqn. 1)(eqn. 1) [2]. [2].

-15--15-

The wind speed in the open air around the collector is The wind speed in the open air around the collector is significantly less than the air velocity through the air channel [significantly less than the air velocity through the air channel [66].].

The chimney can make particularly good use at nights The chimney can make particularly good use at nights when the outside temperature Twhen the outside temperature T00 is very low.is very low.

At nights?At nights?

-16--16-

nn~~ H Hcc / / TT00 (eqn.1) (eqn.1)

The chimney should be as tall as possible.The chimney should be as tall as possible.

Why?Why?

The ground heats up during the day time and The ground heats up during the day time and emits its heat at night [emits its heat at night [77].].

How?How?

2.3.1. Construction of the Chimney2.3.1. Construction of the Chimney

SizeSize : : The chimney must be as tall as The chimney must be as tall as possible.possible.

Life SpanLife Span : : The life span of the chimney The life span of the chimney depends on its material and its standing style. depends on its material and its standing style. The chimneys can be classified into two The chimneys can be classified into two groups in terms of their standings: groups in terms of their standings:

Free-standing (reinforced concrete),Free-standing (reinforced concrete),Guyed tubes as shown in the Figures 8 and 9.Guyed tubes as shown in the Figures 8 and 9.

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Fig.9 Guyed Tubes [2].Fig.9 Guyed Tubes [2].

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Fİg.8 Free-standing (reinforced Fİg.8 Free-standing (reinforced

concrete) [2].concrete) [2].

The life span of a reinforced concrete The life span of a reinforced concrete tower in a dry climate is at least 100 years. tower in a dry climate is at least 100 years. On the other hand, guyed tubes has a On the other hand, guyed tubes has a shorter life span. shorter life span.

Besides these, altough the efficiency Besides these, altough the efficiency of the chimney increases by the increase of the chimney increases by the increase in height, there is a practical limitation for in height, there is a practical limitation for building such a long chimney. The ideal building such a long chimney. The ideal height is 1000 m.height is 1000 m.

-19--19-

3. Cost3. Cost

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 calculated. The energy production costs of the solar chimney, coal and combined cycle power plants are charted by "Energie in Baden-Württemberg“ as shown in the Table 1 [4].

-20--20-

energy production costs

Comparison between the energy production costs of two 200 MW solar chimneys and400 MW coal and combined cycle power plants according to the present business managerialcalculations. 

Comparison between the energy production costs of two 200 MW solar chimneys and 400 MW coal and combined cycle power plants according to the present business managerial calculations. 

Table 1 Energy Production Costs [4].

-21--21-

In short term, it may seem more expensive than the other resources.

In long term, since solar chimney has no ecological harm and no consumption of resources, not even for the construction, it has more advantages. The Chart 1 shows the solar chimney’s costs in 40 years.

-22--22-

Chart 1 Energy Production Costs from Solar Chimneys, Coal and Combined Cycle Power Plants Depending on the Interest Rate [4]. -23--23-

4.4. ConclusionConclusion

To sum up, the principle of the To sum up, the principle of the chimney consists of three basic steps: chimney consists of three basic steps:

Hot air is produced by the sun under a Hot air is produced by the sun under a large roof. large roof.

This flows to a chimney in the middle of This flows to a chimney in the middle of the roof and is drawn upwards. the roof and is drawn upwards.

This updraft drives turbines installed at the This updraft drives turbines installed at the base of the chimney, and the electricity is base of the chimney, and the electricity is produced [2].produced [2].

-24--24-

Generating electricity from the solar Generating electricity from the solar energy is important, especially for future, energy is important, especially for future, since it is unlimited. The solar chimney is a since it is unlimited. The solar chimney is a cheap and useful example of this energy.cheap and useful example of this energy.

The other sources of energy will The other sources of energy will become exhausted but sunlight will still be become exhausted but sunlight will still be falling on earth with undiminished strength falling on earth with undiminished strength for many many years [8]. for many many years [8].

-25--25-

ReferencesReferences1. Williams,J.R.(1977).Technology and 1. Williams,J.R.(1977).Technology and applications;Ann Arbor Science Publishers applications;Ann Arbor Science Publishers Inc,p.138,139.Inc,p.138,139.

2. Schlaich,J.(1995).The Solar Chimney;Edition 2. Schlaich,J.(1995).The Solar Chimney;Edition Axel Menges,p.7,16-21,27,51,53.Axel Menges,p.7,16-21,27,51,53.

3. Taylor,R.H.(1983).Alternative energy 3. Taylor,R.H.(1983).Alternative energy Sources;Adam Hilger Ltd,p.292.Sources;Adam Hilger Ltd,p.292.

4. Solar Chimney-Technology.Retrieved 28 4. Solar Chimney-Technology.Retrieved 28 November 2002 from;November 2002 from;httphttp://www.sbp.de/de/html/projects/solar/aufwind/p://www.sbp.de/de/html/projects/solar/aufwind/pages_auf/enprocos.ages_auf/enprocos.htmhtm..

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5. Solar Chimney-Technology.Retrieved 11 5. Solar Chimney-Technology.Retrieved 11 November 2002 from;November 2002 from;

http://www.sbp.de./de/html/projects/solar/aufwind/pahttp://www.sbp.de./de/html/projects/solar/aufwind/pages_auf/techno.htmges_auf/techno.htm..

6. Solar Chimney Power Plant versus Wind from the 6. Solar Chimney Power Plant versus Wind from the Sun Power Plant.Retrieved 11 November 2002 from;Sun Power Plant.Retrieved 11 November 2002 from;httphttp://www.windfromthesun.com/questions.htm://www.windfromthesun.com/questions.htm..

7. Solar Chimney-Principle.Retrieved 11 November 7. Solar Chimney-Principle.Retrieved 11 November 2002 from;2002 from;

http://www.sbp.de./de/html/projects/solar/aufwind/pahttp://www.sbp.de./de/html/projects/solar/aufwind/pages_auf/principl.htmges_auf/principl.htm..

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8. Messl,H. and Butler,S.T.(1974).Solar 8. Messl,H. and Butler,S.T.(1974).Solar Energy;Pergamon Press,p.276Energy;Pergamon Press,p.276..

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