The Solar Chimney

1
The Solar Chimney

• Solar Energy-1
• Physics 471
• 2004-1
• Presented ByVolkan CIRDAKLI
• InstructorProf. Dr. Ahmet ECEVIT

2
Contents

• Introduction
• The Solar Chimney
• Parts of the Solar Chimney
• Collector
• Turbines
• Chimney
• Working Principles of Solar Chimney
• Technology
• The Energy Storage In the Collector
• Cost
• The Mildura Solar Chimney

3
Contents

• Advantages
• Disadvantages
• Conclusion
• References

4
1.Introduction

• In many parts of the worldthere is a growing
  awareness that some alternative energy sources
  could have an important role to play in the
  production of electricity.
• Howeveronly the solar energy represents totally
  nonpolluting inexhaustible energy resource that
  can be utilized economically to supply Mans
  energy needs for all time 1.

5
Fig. 1 The Prototype Manzanares Solar Chimney 2.

• There are lots of methods of using the solar
  energy and the Solar Chimney is one of them
  which can be seen below in figure 1.

6
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
  collectorturbines and the chimney.

7
2.a. Parts of the Solar Chimney

• 2.a.i. The Collector
• Collector is the partwhich is used to produce
  hot air by green-house effect. It is usually 5-6
  meters high and covers a very large area about
  thousands of m² as seen in figure 2.

Collector
Fig. 2 The Collector 2.

8

• 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.
9

• There is no limitation for the surface area. The
  larger the area the more energy generated from
  the chimney.
• There should be slightly increasing height
  towards to the chimney in order to obtain minimum
  friction loss.
• Covering materials may be different such as
  glass plastic film or glazed collector.The most
  efficient one is glazed collector.It can convert
  up to 70 of irratiated solar energy into heat a
  typical annual average is 50. Also with proper
  maintenance its life span can easily be 60 years
  or more.

10

• 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.
11

• Turbines are placed horizontally in chimney
  vertically in the collector.In order to obtain
  maximum energy from the warmed airturbines
  blades should cover all the cross-sectional area
  of the chimney.
• To do thisone big turbine or a few small
  turbines should be used in chimney as can be
  seen from the figure 5. and figure 6.

12
Fig. 5 Turbine with large diameter 5.
Fig. 6 Small turbines 5.
13

• 2.a.iii. The chimney
• The most important part of the plant is the
  chimneyseen in figure 7. It acts as a thermal
  engine. Since the friction loss is minimum in the
  chimney it likes a pressure tube.

Chimney
Fig. 7 The chimney 2.
14

• 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
15
Although the efficiency is proportional to the
height of the chimney there is a limitation in
practice.

• There are two types of different chimneys using
  for the plant. Free standing 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.

16

• Fig. 8 Free-standing 5.

Fig. 9 Guyed Tubes 5.
17
2.b. Working principles of Solar Chimney

• Transparent roof which is seen in figure 10
  admits the short wave solar radiation component
  and retains long-wave radiation from the heated
  ground. Thus when solar radiation pass through
  the transparent roof it is absorbed by the ground
  elements and it converts into heat energy.

Fig. 10 Transparent roof 4.
18

• Since air is heated it starts to rise up and
  move towards to chimneyseen in figure 11. Also
  it gains velocity.

• Heated air enters the chimney placed at the
  center of the roof and creates an up draught
  there.
• Inside the chimney turbines with electric
  generatorproduce electricity 6.

Fig. 11 Schematic seen of the solar chimney 6
19
Collector Efficiency
Heat Output
Collector Area
Solar Radiation
The temperature differences between the collector
and out flow
Mass flow
Chimney cross-section area
Specific heat capacity of the air
Air speed at collector outflow
Specific dendsity of air at temperature To T
at collector outflow
20

• Comparing with the collector and turbine the
  chimney efficiency is relativelly low. For
  example at a height 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  
21

• Answer First the wind turbines enclosed in a
  pipe can produce 8 times 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 velocity through
  the air channel 7.

22
2.c. Technology

• Solar chimneys are large-scale power plants with
  an output of 5 to 200 MW each 4.
• A 100 MW plant will produce about 750 GWh/year at
  2.300 kWh/m² global horizontal radiation 4.
• For that the glass roof has to be several
  kilometers in diameter and the tube has to be as
  high as possible to achieve a large annual output
  4.

23

• The turbines are basically more closely
  related to the pressure-staged
  hydroelectric turbines than to the speed-stepped
  wind turbines. Therefore they have been developed
  and designed in collaboration with hydroelectric
  power plant manufacturers 4.
• The turbines life span is based on its
  resistance to rapid pressure and speed changes of
  the air 5.

24
3.The Energy Storage In the Collector

• Since collectors produce hot air by green house
  effect to produce electric during the night
  tight water-filled tubes are placed under the
  roof as seen in figure 12. 6.

Day
Night
Fig. 12 Principle of heat storage underneath the
roof using water-filled black tubes 6.
25

• 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 cm depending on the desired power output 5.

26
4.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 compiled. We asked the utility Energie
  Baden Württemberg to determine the energy
  production costs compared to coal- and combined
  cycle power plants based on equal and common
  methods 8. (Table. 1).

27
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.
28
Fig. 13 Energy production costs from solar
chimneys coal and combined cycle power plants
depending on the interest rate 8.
29
5.The Mildura Solar Chimney

• The 1000m Solar Chimney in Mildura Australia
  will be the highest man-made structure on Earth
  and can produce 200MW of electricity providing
  power to 200000 homes.Schematic seen of a
  construction of a chimney is in figure 14.

Fig. 14 Construction of a chimney 2.
30

• The cost to build the tower is estimated at 395
  million. (About 14 percent 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 (9500
  GigaWatt hours) could be met easily2.

31

• Details of the solar chimney are as
  followsLocation Mildura AustraliaType
  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 very simple 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
  yearCompany Enviromission LtdConstruction
  time About 18-24 monthsExpected completion
  date 2005 2.

32
6.Advantages

• Solar chimney power stations are particularly
  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.

33

• 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
  are everywhere in sufficient quantities.
• No ecological harm and no consumption of
  resources.

34
7.Disadvantages

• Some estimates say that the cost of generating
  electricity from a solar chimney is 5x more than
  from a gas turbine. Although fuel is not
  required solar chimneys have a very high capital
  cost 2.
• The structure itself is massive and requires a
  lot of engineering expertise and materials to
  construct 2.

35
8.Conclusion

• Solar chimney power stations could make important
  contributions to the energy supplies in Africa
  Asia and Australia because there is plenty of
  space and sunlight available there 2.
• It is very important for the future because our
  resources are limited except our sun.

36
References

• WilliamsJ.R.(1977).Technology and
  applicationsAnn Arbor Science Publishers Inc.
• A brief history of solar chimney.Retrieved
  10.11.2004 from http//www.visionengineer.com/
  env/solar_flue.shtml
• TaylorR.H.(1983).Alternative energy SourcesAdam
  Hilger Ltdp.292.
• Solar Chimney-Technology.Retrieved 10.11.2004
  from
• http//www.sbp.de./de/html/projects/solar/aufwind
  /pages_auf/techno.htm.

37

• SchlaichJ.(1995).The Solar ChimneyEdition Axel
  Menges
• Solar Chimney-Principle.Retrieved 10.11.2004
  from
• http//www.sbp.de./de/html/projects/solar/aufwind
  /pages_auf/principl.htm.
• 7. Solar Chimney Power Plant versus Wind from
  the Sun Power Plant.Retrieved 10.11.2004 from
• http//www.windfromthesun.com/questions.htm
• 8. Solar Chimney-Energy cost.Retrieved
  10.11.2004 from
• http//www.sbp.de/de/html/projects/solar/aufwind/
  pages_auf/enprocos.htm