??????? SOLAR CHIMNEY ???????

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??????? SOLAR CHIMNEY???????

• Phys 471 (Solar Energy)
• 2001-2002/2
• Instructor Prof. Dr. Ahmet Ecevit
• Presented by Ebru Koç , Özlem Çiçek

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Table of contents
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• 1. Introduction .................................
  ..... 5
• 2. How does a solar chimney work?...... 6
• 3. The technology.................................
  .. 8
• 3.1 The Collector.................................
  ... 8
• 3.2 The Energy Storage..........................
  9
• 3.3 The Chimney...................................
  .11
• 3.4 The Turbines..................................
  ..12

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• 4. A Hydroelectric power station for the
  desert....... 14
• 4.1 A summary of How it work?..................
  .....15
• 4.2 Some similarities between them...............
  .......16
• 5. The Prototype in Manzanares....................
  ............18
• 6. Designing large solar chimney..................
  ............22
• 7. Energy production cost.........................
  .................29
• 8. Physical principles of solar
  chimney.....................33
• 8.1 Approach calculating efficiency..............
  ........34
• 9. Advantages of solar chimney ...................
  ............45
• 10. Disadvantages of solar chimney
  .........................48
• 11. Conclusion....................................
  .......................49
• 12. References....................................
  ........................51

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SOLAR CHIMNEY
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Fig.1. Working principles of Solar Chimney1
ELECTRICITY FROM SUN
5
INTRODUCTION
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• Man learned to make active use of solar energy
  at a very early stage greenhouses help to grow
  food, chimney suction ventilated and cooled
  buildings, wind mills ground corn and pumped
  water2.

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HOW DOES A SOLAR CHIMNEY WORK?
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Incident solar radiation heats the air under a
large transparent collector roof. The temperature
difference causes a pressure drop over the height
of chimney resulting in an upwind which is
converted into mechanical energy by the turbines
and then into electricity via conventional
generators3.
Fig.2. Principle of the solar chimney glass roof
collector, chimney tube, wind turbines4.
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Thus the solar chimney combines 3 well-known
technologies in a novel way5.

• the glass roof hot air collector

• the chimney

• wind turbines with generator

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3. THE TECHNOLOGY
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• 3.1 THE COLLECTORHot air is produced by the
  greenhouse effect. The collector consisting of
  plastic film or glass plastic film. The roof
  material is stretched horizontally 2 or 6 m 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 loss2.

Fig.4. The collector
Fig.3. Principle of the solar chimney6.
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• 3.2 THE ENERGY STORAGE Water filled black tubes
  are laid down side by side on the black sheeted
  or sprayed soil under the glass roof collector.
  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 2.

10
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Fig.5. Principle of heat storage underneath the
roof using water-filled black tubes 3.

• 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 2.

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• 3.3 THE CHIMNEYThe chimney itself is the plant's
  actual thermal engine. It is a pressure tube with
  low friction loss because of its optimal
  surface-volume ratio. The upthrust of the air
  heated in the collector is approximately
  proportional to the air temperature rise .Tcoll
  in the collector and the volume, of the chimney.
  In a large solar chimney the collector raises the
  temperature of the air by about 35. This
  produces an updraught velocity in the chimney of
  about 15m/s. It is thus possible to enter into an
  operating solar chimney plant for maintenance
  without difficulty 2.

Fig.6. Solar Chimney1
12
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• The chimney height is affected by collectors
  glass.
• 1. If glass is cheap and concrete expensive
  then the collector will be large with a high
  proportion of double glazing and a relatively low
  chimney.
• 2. If glass is expensive there will be a
  smaller, largely single-glazed collector and a
  tall chimney.

Fig.7. Solar Chimney Prototype at Manzanares
(Spain)
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• 3.4 THE TURBINES Using turbines, mechanical
  output in the form of rotational energy can be
  derived from the air current in the chimney.
  Blade pitch is adjusted during operation to
  regulate power output according to the altering
  airspeed and airflow. If the flat sides of the
  blades are perpendicular to the airflow, the
  turbine does not turn. If the blades are parallel
  to the air flow and allow the air to flow through
  undisturbed there is no drop in pressure at the
  turbine and no electricity is generated. Between
  these two extremes there is an optimum blade
  setting the output is maximized if the pressure
  drop at the turbine is about two thirds of the
  total pressure differential available 2.

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4. A 'HYDROELECTRIC POWER STATION FOR THE DESERT
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A solar chimney is a kind of Hydroelectric Power
Station for a desert
Fig.8. Toledo Bend Dam Hydroelectric Power Plant
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4.1 A Summary of How It Works Water from the
reservoir enters the intake (1) through the open
intake gates (2) the water flows down the power
tunnel (3) through the wicket gates (4) which can
be controlled automatically or manually. It then
continues past the turbine blades (5) which turn
the generator (6) at a constant 100 revolutions
per minute (RPM), changing the mechanical energy
into electrical energy 7.
Fig.9. Hydroelectric Power Cycle 7.
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4.2 Some similarities between them
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• Solar chimneys are technically very similar to
  hydroelectric power stations - so farthe only
  really successful large scale renewable energy
  source the collector roof is the equivalent of
  the reservoir, and the chimney of the penstock.
  Both power generation systems work with
  pressure-staged turbines, and both achieve low
  power production costs because of their extremely
  long life-span and low running costs. The
  collector roof and reservoir areas required are
  also comparable in size for the same electrical
  output. But the collector roof can be built in
  arid deserts and removed without any difficulty,
  whereas useful land is submerged under reservoirs.

17
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• Solar chimneys work on dry air and can be
  operated without the corrosion and cavitation
  typically caused by water. They will soon be just
  as successful as hydroelectric power stations.
• Electricity yielded by a solar chimney is in
  proportion to the intensity of global solar
  radiation, collector area and chimney height 2.

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5.The prototype in Manzanares
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Fig.10. Prototype of the solar chimney at
Manzanares 8.
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• The aim of this research project was to verify,
  through field measurements, the performance
  projected from calculations based on theory, and
  to examine the influence of individual components
  on the plant's output and efficiency under
  realistic engineering and meteorological
  conditions.

Fig.10. Prototype of the solar chimney at
Manzanares 8.
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• To this end a chimney 195 m high and 10 m in
  diameter was built, surrounded by a collector 240
  m in diameter. The plant was equipped with
  extensive measurement data acquisition
  facilities. The performance of the plant was
  registered second by second by 180 sensors.

Fig.10. Prototype of the solar chimney at
Manzanares 8.
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• A realistic collector roof for large-scale
  plants has to be built 2 to 6 metres above ground
  level. For this reason the lowest realistic
  height for a collector roof for large-scale
  technical use, 2 metres, was selected for the
  small Manzanares plant. (For output, a roof
  height of 50 cm only would in fact have been
  ideal.) Thus only 50 kW could be achieved in
  Manzanares, but this realistic roof height also
  permitted convenient access to the turbine at the
  base of the chimney. During the 32 month period,
  plant reliability was over 95 2.

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6. Designing Large Solar Chimneys 2
Measurements taken from the experimental
plant in Manzanares and solar chimney
thermodynamic behaviour simulation programs were
used to design large plants with outputs of 200
MW and more. This showed that thermodynamic
calculations for collector, tower and turbine
were very reliable for large plants as well.
Despite considerable area and volume differences
between the Manzanares pilot plant and a
projected 100 MW facilities, the key
thermodynamic factors are of similar size in both
cases.
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It includes thermodynamic calculations by
computer simulation and an analysis of technical
feasibility as seen in the table I.
With 2300 kWh/m2y global radiation
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) Pa 28.6 62.9 80.6
Pressure Drop at turbine Pa 314.3 629.1 902.4
Table. I Thermodynamics Data
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The overall performance of the plant, by
day and by season, given the prescribed climate
and plant geometry, considering all physical
phenomena including single and double-glazing of
the collector, ground storage, condensation
effects and losses in collector, and turbine, can
be calculated. Reliable statically and
dynamic calculation and construction for chimney
about 1,000 metres high (slenderness
ratioheight/diameter lt10) is possible without
difficulty today (Figure.11)
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0,25m
1000m 840m 660m 500m
0,25m
0,32m
0,41m
0,53m
0,68m
0,87m
0,99m
Figure (11) Wall thickness of a chimney tube
1.000 m high and 170 m diameter and 1.000m
chimney tube under construction.
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With the support of a German and an Indian
contractor especially experienced in building
cooling towers and chimneys, manufacturing and
erection procedures were developed for various
types in concrete and steel and their costs
compared. The type selected is dependent on the
site. If sufficient concrete aggregate materials
are available in the area and anticipated seismic
acceleration is less than 9/3, then reinforced
concrete tubes are the most suitable.
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There is no physical optimum for solar
chimney cost calculations, even when
meteorological and site conditions are precisely
known. Tower and collector dimensions as seen
table 2 for a required electrical energy output
can be determined only when their specific
manufacturing and erection costs are known for a
given site.
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Dimensions
With 2300 kWh/m2y global radiation
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
Table. 2 Typical Dimensions for Solar Chimneys
With Different Power
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7. Energy Production Costs 2
With the support of construction companies,
the glass industry and turbine manufacturers are
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.
30
Table 3 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.
31
Purely under commercial aspects with a
gross interest rate of about 11 and a
construction period of 4 years during which the
investment costs increase already by 30 (!)
Electricity from solar chimneys is merely 20
more expensive than from coal. By just reducing
the interest rate to 8 electricity from solar
chimneys would become competitive today.
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.
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Fig. (12 ) Energy production costs from solar
chimneys, coal and combined cycle power plants
depending on the interest rate.
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8. Physical Principles of the Solar Chimney
Precise description of the output pattern
of a solar chimney under given meteorological
boundary conditions and structural dimensions is
possible only with an extensive thermodynamic and
flow dynamic computer program. This includes the
equations which reflect the effect of heat
transfer between the ground and air in the
collector, friction loss in the collector and
chimney, heat storage in the ground, the turbine
and its power control 9. The power output
of a solar chimney are presented here in a
simplified form
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8.1 Approach Calculating Efficiency
The Collector
.
A solar chimney collector converts
available solar radiation G onto the collector
surface Acoll into heat output. Collector
efficiency ncoll can be expressed as a ratio of
the heat output of the collector as heated air Q
and the solar radiation G(measured in W/m2) times
Acoll.
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.
Q Heat output of the collector
.
m mass flow
Cp Specific heat capacity of the air
?cool Specific density of air at tempereature
To ?T
Vcoll Vc Air speed at collector
outflow/chimney inflow
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For collector efficiency this gives
a Effective absorption coefficient of the
collector
ß Loss correction value (in W/m2K), allowing
for emission and convection loss
37
Thus collector efficiency can also be expressed
like this
The link between air speed at the collector
outflow Vcoll and the temperature ?T can be
expressed
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The simple balance equation is independent of
collector roof height because friction losses and
ground storage in the collector are neglected

• 0.75-0.8

Thus, with radiation of 1000 W/m2 a collector
efficiency of 62 is established.
ß 5-6 W/m2
G1000 W/m2 ?T300C
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The Chimney
.
The chimney converts the heat flow Q produced by
the collector into kinetic energy and potential
energy (pressure drop in the turbine). Thus, the
density difference of the air is caused by
temperature rise in the collector works as a
driving force.
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in differential form
HC
And
Fig. (13) Chimney
g acceleration due to gravity HC Chimney
height ? density
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?Ptot ?PS?Pd
The static pressure difference drops at the
turbine, the dynamic component describes the
kinetic energy of the air flow.
so
?Ptot?Pd
?PS O
The power contained in the flow Ptot
?ptotVC,max AC
Efficiency of the chimney
Maximum flow speed
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The Wind Turbine
The wind turbine fitted at the base of the
chimney converts free convection flow in to the
rotational energy. The pressure drop across the
turbine can be expressed in a first approximation
by the Bernoulli equation
The pressure drop
The appropriate charesteristic curve is expressed
by
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Thus mechanical power taken up by the turbine is
Powerwt,max (2/3)ncoll nc Acoll G
Powerwt,max (2/3)ncoll(g/CpTo)HcAcollG
It is recognized that the electrical ouput
of the solar chimney is proportional to Hc
Acoll, i.e to the volume included within the
chimney height and collector area.
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The dimensions of a 30 MW lant listed in the
table 2 9.
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)x750x375
1000x1000
Pelectric 30 MW
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Solar chimneys operate simply and have a
number of advantages.

• 9. Advantages 2
• The collector can use all solar radiation, both
  direct and diffused. The other major scale solar-
  thermal power plants, which apply concentrators
  and therefore can use only direct radiation. 

2 Due to the heat, storage system the solar
chimney will operate 24h on pure solar energy.
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3. Solar chimneys are particularly reliable and
not liable to break down, in comparison with
other solar generating plants.
4. Unlike conventional power stations, solar
chimneys do not need cooling water.
5. The building materials needed for solar
chimneys, mainly concrete and glass, are
available everywhere in sufficient quantities.
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6. Solar chimneys can be building now, even in
less industrially developed countries. No
investment in high-technology manufacturing plant
is needed.
7. Even in poor countries, it is possible to
build a large plant without high foreign currency
expenditure by using their own resources and work
force this creates large numbers of jobs and
dramatically reduces the capital investment
requirement and the cost of generating
electricity.
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10. Disadvantages 3
1. Solar chimneys can covert only a small
proportion of the solar heat collected into
electricity, and thus have a poor efficiency
level. However, they make up for this
disadvantage by their cheap, robust construction,
and low maintenance costs.
2. Solar chimneys need large collector areas. As
economically viable operation of solar
electricity production plants is confined to
regions with high solar radiation, this is not a
fundamental disadvantage as such, regions
usually have enormous deserts and unutilised
areas.
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11. CONCLUSION
Why do we use solar power?
Current energy production from coal and oil
is damaging to the environment and non-renewable.
Inadequate energy supplies can lead the poverty,
which commonly results in population explosions.
Solar energy is the answer.
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Sensible technology for the use of solar power
must -Be simple and reliable, -Be accessible to
the technologically less developed countries that
are sunny and often have limited raw materials
resources, -Not need cooling water or produce
waste heat, -Be based on environmentally sound
production from renewable materials.
 THE SOLAR CHIMNEY MEETS THESE CONDITIONS
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REFERENCES
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• 1. www.argonet.co.uk/users/bobsier/sola6.html
• 2.wire0.isses.org/wire/publications/Research.nsf/0
  0a329276ae7f371c125680e003falf3/0DED34BF3EB9A985C1
  2569840055F09E/File/SolarChimney_short_version.pd
  f
• 3. Schlaich J. Engineering structures 21, 1999,
  pp 664-668
• 4. http//www.solarserver.de/lexikon/aufwindkraftw
  erk.jpg
• 5. Schlaich J. The Solar Chimney, Edition Axel
  Menges, Stuttgart, 1995, pp.18
• 6. Schlaich J. Renewable Energy Structures,
  Structural Engineering International 1994 4(2),
  pp.76-81.
• 7. http//www.toledo-bend.com/toledo_bend/index.as
  p?requesttolbenddam
• 8. Schlaich Bergermann and Partner Structural
  Consulting Engineers Stuttgart
• 9. Schlaich, J. (1995). Solar Chimney
  Electricity from the Sun. Stuttgart Edition Axel
  Menges, pp.54-55.

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