471-2004-1-solarchimneys-VolkanCirdakli (1)

8/3/2019 471-2004-1-solarchimneys-VolkanCirdakli (1)

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The Solar Chimney

Solar Energy-1

Physics 471

2004-1Presented By:Volkan CIRDAKLI

Instructor:Prof. Dr. Ahmet ECEVIT


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Contents:

1. Introduction2. The Solar Chimney

a. Parts of the Solar Chimneyi. Collector

ii. Turbinesiii. Chimney

b. Working Principles of Solar Chimney

c. Technology

3. The Energy Storage In the Collector

4. Cost

5. The Mildura Solar Chimney


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6. Advantages

7. Disadvantages

8. ConclusionReferences

Contents:


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1.Introduction:

In many parts of the world,there is agrowing awareness that some

alternative energy sources could have

an important role to play in the

production of electricity.

However,only the solar energy

represents totally nonpolluting

inexhaustible energy resource thatcan be utilized economically to

supply Mans energy needs for

all time [1].


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Fig. 1 The Prototype Manzanares Solar

Chimney [2].

There are lots of methods of using the

solar energy , and the Solar Chimneyis one of them, which can be seen

below, in figure 1.


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2.The Solar Chimney

In 1978, it was suggested by

Professor Schlaich of Stuttgart

university that power could be

produced by a hybrid solar system

[3]. The solar chimney system

consists of three parts; The

collector,turbines and the chimney.


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2.a. Parts of the Solar Chimney2.a.i. The CollectorCollector is the

part,which is usedto produce hot air

by green-houseeffect. It is usually

5-6

meters high andcovers a very largearea aboutthousands of m as

seen in fgure 2.

Fig. 2 The Collector [2].

Collector


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Since glazing increases the mass of

the roof, glazed collectors should

have stronger rods and should be

attached as in figure 3.

Fig. 3 The glazed collector roof of Solar Chimney [4].


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There is no limitation for the surface area. Thelarger the area, the more energy generated fromthe chimney.

There should be slightly increasing heighttowards to the chimney in order to obtainminimum friction loss.

Covering materials may be different, such as;glass, plastic film or glazed collector.The mostefficient one is glazed collector.It can convert upto 70% of irratiated solar energy into heat a

typical annual average is 50%. Also, with propermaintenance, its life span can easily be 60 yearsor more.


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2.a.ii. Turbines

Turbines, seen in figure 4, are used to convert

air current to the mechanical energy.

Fig. 4 Turbine for Solar Chimney Power Station [2].


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Turbines are placed horizontally in

chimney, vertically in the collector.Inorder to obtain maximum energy

from the warmed air,turbines blades

should cover all the cross-sectional

area of the chimney.

To do this,one big turbine or a few

small turbines should be used in

chimney, as can be seen from thefigure 5. and figure 6.


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Fig. 5 Turbine with large diameter [5]. Fig. 6 Small turbines [5].


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2.a.iii. The chimney

The most importantpart of the plant is

the chimney,seen in

fgure 7. It acts as a

thermal engine.Since the friction

loss is minimum in

the chimney it likesa pressure tube.

Chimney

Fig. 7 The chimney [2].


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Longer the chimneys height, the more the

energy produced from the chimney. The efficiency of the chimney is not

depend on the amount of the temperature

rising, but depends on the outside

temperature.

Thus, efficiency directly proportional to the

ratio between the height of the chimney and

the outside temperature. [5]


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There are two types of different

chimneys using for the plant. Freestanding chimneys and guyed tubes

(Figure 8. and figure 9. ) .

The life span of a free standing

chimney is longer than that of the

guyed tubes. It lasts about a hundred

years, while the guyed tubes is much

shorter.

Although, the efficiency is

proportional to the height of the

chimney, there is a limitation inpractice.


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Fig. 8Fig. 8 FreeFree--standingstanding [5].[5]. Fig.Fig. 99 Guyed Tubes [5].Guyed Tubes [5].


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2.b. Working principles of

Solar ChimneyTransparent roof, which isseen in fgure 10, admits theshort wave solar radiationcomponent and retains long-wave radiation from the heatedground. Thus, when solar

radiation pass through thetransparent roof it is absorbedby the ground elements and itconverts into heat energy.

Fig. 10 Transparent

roof [4].


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Since air is heated, it starts to rise up

and move towards to chimney,seen in

fgure 11. Also, it gains velocity.Heated air enters the

chimney placed at the

center of the roof andcreates an up draught

there.

Inside the chimney,turbines with electric

generator,produce

electricity [6].

Fig. 11 Schematic seen of

the solar chimney [6]


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Heat Output

Collector Area Solar Radiation

Specific heat capacity

of the air

Mass flow

Collector Efficiency

The temperature

differences between the

collector and out flow

Air speed at collector outflow

Specific dendsity of air at temperatureTo + T at collector outflow

Chimney cross-section area


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Comparing with the collector and

turbine, the chimney efficiency is

relativelly low. For example, at aheight of 1000 meters, chimney

efficiency is somewhat greater than

3% [5].

So, Why use a pipe or air channel to

enclose the turbines? Why not have a

large "wind farm," with turbines

mounted on towers in the open air? ,


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Answer: First, the wind turbines

enclosed in a pipe can produce 8times as much power for a given

wind speed than a turbine in the open

air. Second, the wind farm concept

would require a much larger number

of turbines. Also, the wind speed in

the open air around the collector is

significantly less than the air velocitythrough the air channel [7].


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2.c. TechnologySolar chimneys are large-scale powerplants with an output of 5 to 200 MW

each [4].

A 100 MW plant will produce about 750

GWh/year at 2.300 kWh/m global

horizontal radiation [4].

For that the glass roof has to be several

kilometers in diameter and the tube has tobe as high as possible to achieve a large

annual output [4].


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The turbines are basically

more closely related to thepressure-staged hydroelectric

turbines than to the speed-stepped

wind turbines. Therefore they have

been developed and designed incollaboration with hydroelectric

power plant manufacturers [4].

The turbines life span is based onits resistance to rapid pressure and

speed changes of the air [5].


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3.The Energy Storage In the

CollectorSince collectors produce hot air bygreen house effect, to produce electric

during the night, tight water-filled

tubes are placed under the roof, asseen in fgure 12. [6].

Day Night

Fig. 12 Principle of heat storage underneath the roof using water-filled black

tubes [6].


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The water heats up during the

daytime and emits its heat at night. These tubes are filled only once, no

further water is needed, because the

tubes remain closed after filling

process.

The volume of water in the tubes is

selected to correspond to a water

layer with a depth of 5 to 20 cmdepending on the desired power

output [5].


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4.Cost

With the support of constructioncompanies, the glass industry and

turbine manufacturers a rather exact

cost estimate for a 200 MW solar

chimney could be compiled. We

asked the utility "Energie Baden

Wrttemberg" to determine the

energy production costs compared tocoal- and combined cycle power

plants based on equal and common

methods [8]. (Table. 1).


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Table 1. Comparison between the energy production costs of two x 200

MW solar chimneys and 400 MW coal and combined cycle power plants

according to the present business managerial calculations [8].


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Fig. 13 Energy production costs from solar chimneys, coal and

combined cycle power plants depending on the interest rate [8].


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5.The Mildura Solar Chimney

The 1000m SolarChimney in Mildura,Australia, will be thehighest man-madestructure on Earth, andcan produce 200MW ofelectricity, providing

power to 200,000homes.Schematic seenof a construction of achimney is in figure 14.

Fig. 14 Construction of a

chimney [2].


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The cost to build the tower is

estimated at $395 million. (About 14percent more than an equivalent coal-

fired power station, and about 70

percent more per installed megawatt

than a comparable wind farm).

The Australian government target of

producing 2% of energy from

renewable sources by 2010 (9500GigaWatt hours) could be met

easily[2].


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Details of the solar chimney are as follows:

Location: Mildura, Australia

Type: Solar Tower power plant with steel-

reinforced concrete tower and steel/glass solar air

collector (alternatively with polymer glazing)

Features: The base of the tower will be between

170 to 200 metres. The chimney is basically a verysimple tube with wall thickness of 25cm, diameter

of 150m and a height of 1000m. The collector roof

will be 5000m in diameter.

Power: Up to 500 Gigawatt hours per year

Company: Enviromission LtdConstruction time: About 18-24 months

Expected completion date: 2005 [2].


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6.Advantages

Solar chimney power stations areparticularly suitable for generating

electricity in deserts and sun-rich

wasteland.

It provides electricity 24 hour a

day from solar energy alone.

No fuel is needed. It needs no

cooling water and is suitable in

extreme drying regions.


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It is particularly reliable and a little

trouble-prone compared with other

power plants.

The materials concrete, glass and

steel necessary for the building of

solar chimney power stations areeverywhere in sufficient quantities.

No ecological harm and no

consumption of resources.


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8.Conclusion

Solar chimney power stations couldmake important contributions to the

energy supplies in Africa, Asia and

Australia, because there is plenty ofspace and sunlight available there [2].

It is very important for the future,

because our resources are limited,

except our sun.


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References:1. Williams,J.R.(1977).Technology and

applications;Ann Arbor Science PublishersInc.

2. A brief history of solar chimney.Retrieved10.11.2004 from;

http://www.visionengineer.com/env/solar_flue.shtml

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

4. Solar Chimney-Technology.Retrieved10.11.2004 from;

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


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5. Schlaich,J.(1995).The SolarChimney;Edition Axel Menges

6. Solar Chimney-Principle.Retrieved10.11.2004 from;

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

7. Solar Chimney Power Plant versusWind from the Sun PowerPlant.Retrieved 10.11.2004 from;

http://www.windfromthesun.com/questions.htm

8. Solar Chimney-Energy cost.Retrieved10.11.2004 from;

http://www.sbp.de/de/html/projects/solar/aufwind/pages_auf/enprocos.htm

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