Transcript SOLAR CHIMNEY

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SOLAR CHIMNEY
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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
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
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
Fig.1. Working principles of Solar Chimney[1]
ELECTRICITY FROM SUN
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INTRODUCTION
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 water[2].
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HOW DOES A SOLAR CHIMNEY
WORK?
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
Fig.2. Principle of the solar chimney: glass
conventional generators[3].
roof collector, chimney tube, wind turbines[4].
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Thus the solar chimney combines 3
well-known technologies in a novel
way[5].

the glass roof hot air collector
the
chimney
wind
turbines with generator
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3. THE TECHNOLOGY
3.1 THE COLLECTOR:Hot 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
loss[2].
Fig.3. Principle of the solar chimney[6].
Fig.4. The collector
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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].
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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 CHIMNEY:The 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 Chimney[1]
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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)
3.4
THE
TURBINES:
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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:
A solar chimney
is a kind of
Hydroelectrıc
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:
Fig.9. Hydroelectric Power Cycle [7].
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].
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4.2 Some similarities between them
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.
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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
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].
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.
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
314.3
629.1
902.4
Pressure Drop at turbine
Pa
Table. I: Thermodynamics Data
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 ratio=height/diameter <10) is possible
without difficulty today (Figure.11)
0,25m
1000m
840m
0,25m
0,32m
0,41m
0,53m
0,68m
0,87m
0,99m
660m
500m
Figure (11): Wall thickness of a chimney tube 1.000
m high and 170 m diameter and 1.000m chimney
tube under construction.
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.
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.
Dimensions
With 2300 kWh/m2y global radiation
Power Block
MW
Size
Collector
m
Diameter Dcoll
Chimney
m
Height HC
Chimney
m
Diameter DC
Annual
GWh/y
Energy
Production
5
30
100
200
111
2200
0
3600
4000
445 750
950
1500
54
84
115
175
13.
9
87.4
305.2
600
Table. 2: Typical Dimensions for Solar Chimneys With Different Power
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 BadenWürttemberg" to determine the energy production
costs compared to coal- and combined cycle power
plants based on equal and common methods.
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.
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.
Fig. (12 ) Energy production costs from solar chimneys, coal and combined cycle
power plants depending on the interest rate.
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:
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.
.
Q: Heat output of the collector
.
m: mass flow
Cp: Specific heat capacity of the air
ρ
cool:
Specific density of air at
tempereature To + ΔT
Vcoll= Vc : Air speed at collector
outflow/chimney inflow
For collector efficiency this gives:
α: Effective absorption
coefficient of the collector
β : Loss correction value (in
W/m2K), allowing for
emission and convection loss
Thus collector efficiency can also be expressed like this:
The link between air speed at the collector outflow Vcoll
and the temperature ΔT can be expressed:
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
= 5-6 W/m2
G=1000 W/m2
β
ΔT=300C
Thus, with radiation of
1000 W/m2 a collector
efficiency of 62% is
established.
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.
in differential form
HC
Fig. (13) Chimney
g
: acceleration due to gravity
HC : Chimney height
ρ : density
And
ΔPtot =ΔPS+ΔPd
The static pressure difference drops at the turbine, the
dynamic component describes the kinetic energy of the
air flow. ΔP = O
so ΔP =ΔP
S
tot
d
The power contained in the flow: Ptot= ΔptotVC,max AC
Efficiency of the chimney :
Maximum flow speed:
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:
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.
The dimensions of a 30 MW lant listed in the table 2 [9].
HC: –––––––– 750m
Chimney Height
Dcoll: –––––––– 2200m
Collector Diameter
G: –––––––– 1000W/m2
Solar Irradiation
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
Solar chimneys operate simply and have a number of
advantages.:
9. Advantages [2]
1. The collector can use all solar radiation, both
direct and diffused. The other major scale solarthermal 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.
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.
6. Solar chimneys can be building now, even in less
industrially developed countries. No investment in hightechnology 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.
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.
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.
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
REFERENCES
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1. www.argonet.co.uk/users/bobsier/sola6.html
2.wire0.isses.org/wire/publications/Research.nsf/00a329276ae7f371c125680e003fa
lf3/0DED34BF3EB9A985C12569840055F09E/$File/SolarChimney_short_versi
on.pdf
3. Schlaich J. Engineering structures 21, 1999, pp 664-668
4. http://www.solarserver.de/lexikon/aufwindkraftwerk.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.asp?request=tolbenddam
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.