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Solar Energy I
2001-02-1
Instructor : Prof. Dr. AHMET ECEVIT
Presented by: Yusuf SIMSEK
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TABLE OF CONTENT PAGE
1. Introduction 4
2. The Collector 7
2. Structure of the Collector 8
.
4. The Energy Storage in the Collector 11
. mney
6. Solar Chimney Prototype at Manzanares (Spain) 14
7. Turbines 16
8. How Does Collector Work? 17
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9. Collector Efficiency 21
11. The Chimne 25
12. The Turbine 32
.
14. Typical Dymensions for Solar Chimneys 38
5. Termodynamics
16. Operation 41
17. Technical Data Quantities 42
18. Energy Production Costs 44
19. Conclusion47
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.
Solar chimney converts the solar radiation into electricity. Itconsists of three simple parts:
Glass roof collector
Chimney
Turbine
Basicall air is heated b solar radiation under the lass roof
and it starts to move toward to the chimney. Turbines which are
placed at the base of the chimney converts this mechanical power
. . .
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and a high chimney can be designed to generate 100 to 200 MW
continously 24 h a day. Thus even a small number of solar chimneys
can rep ace a arge nuc ear power s a on. o ar c mneys opera e
simply and have a number of other advantages:
,
Due to the heat storage system the soalr chimney will operate.
Solar chimneys are particularly reliable and not liable to break
down, in com arision with other solar eneratin lants.
Unlike conventional power stations (and also other solar
thermal power station types), solar chimneys do not need cooling
water.
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Unlike conventional power stations (and also other solarthermal power station types), solar chimneys do not cooling
.
The building materials needed for solar chimney, mainly
concrete and lass are available ever where in sufficient
quantities.
Even in poor countries it is possible to build a large plant
without high foreign currency expenditure by using their ownresources and work forces [1].
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2. The Collector
Collector is the part of the chimney that
produce hot air by the green house effect. It
plastic film. The roof material is stretchedhorizontally two or six meter above theChimneygroun . e e g o e roo ncreases
adjacent to the chimney base, so that the air is
diverted to the chimney base with minimumr c on oss. s cover ng a m s e s or
wave solar radiation component and retains
long-wave radiation from the heated ground.
o ec or
us t e groun un er t e roo eats up an
transfers its heat to the air flowing radially
above it from the outside to the chimney [2].Turbine
. .
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3. Structure of the Collector
The structure of the collector changes to the coveringmaterial we used. If we use plastic film we can construct the
s e e on y a us ng e space e ween e ro s as me er.
In this type skeleton attaching plastic film is easy and it is
particularly suitable for very large collector surface in remoteplaces because of the small quantites of the materials needed
and low transportation cost. The 45 000 m2 of the prototype
the optimum and cheapest material in the long life term [3].
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4. Glazed CollectorA flate glazed roof must have much more durable skeleton.
Besause glazing increases the mass of the roof. Its rods are more
stronger and they are attached like in the picture below (Fig. 2.). A
collector roof of this kind has a very long lifespan. With proper
maintanence this can easill be 60 ears or more 4 .
Fig. 2. Collector Glass Roof of Solar ChimneyPrototype at Manzanares from Inside
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A flate glazed collector can convert up to 70% of
irratiated solar energy into heat, dependent on air
throughput, a typical annual average is 50%. Also the
ground under the roof provides natural energy storage
. ,
temperature increases towards tothe tower and energy loss increases
near the chimney. We can increase
the ability of the collector roof by
double lazin about the tower
(Fig. 3).
Fig. 3. Aerial View of Solar
Chimney Prototype at Dusk.
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5. The Energy Storage in the CollectorWater filled black tubes are laid down side by side on
the black sheeted or sprayed soil under the glass roofcollector (Fig. 4). They are filled with water once and remainclosed thereafter, so that no evaporation can take place. Thevolume of water in the tubes is selected to corres ond to awater layer with a depth of 5 to 20 cm depending on the
desired power output.nce e ea rans er e ween ac u es an wa er
is much larger than that between the black sheet and thesoil, even at low water flow speed in the tubes, and since
the heat capacity of water (4.2 kJ/kg) is much higher thanthat of soil (0.75 - 0.85 kJ/kg) the water inside the tubes
night, when the air in the collector cools down [6].
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Fig. 4:Principle of heat storage underneath the roof usingwater-filled black tubes.
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6. Chimney
The chimney is the plants actual
thermal engine (Fig. 5). Its optimal surface-
volume ratio decreases friction loss and makes
it like a pressure tube. The upthrust of the air
proportional to the air temperature rise T in
the collector and the volume of the cchimney.
temperature of the air by about T= 35oC. This
produce an updraught velocity in the chimney
of about V=15m/s [7].
Fig. 5. Chimney
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7. Solar Chimney Prototype at Manzanares
pa n (F g. 6)
only 1.5mm thick
10m diameter
e e o ea ng
was 150mm
vertically at intervals
of 8.6m and shiftened
every 4m y exter or
trussrirelers [8].Fig. 6. Solar Chimney Prototype
at Manzanares
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c mney 195 m g
and 10 m in diameter
surrounded by a collector
240 m in diameter.
Fig. 7. Prototype of the solar chimney at Manzanares.
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8.Turbines
The turbines, the air current is converted into mechanical
energy. The turbines are always placed at a height of 9 meter at the
base of the chimney. According to the size of the turbine, they
placed horizontally (Fig. 8) or verticaly (Fig. 9) and also the number
of the turbines can var .
Fig. 8. Horizontal Fig. 9. Vertical
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9.How Does A Collector
When solar radiation pass
throu h the trans arent roof it is
absorbed by the ground elements andit converts into heat energy. When air
,
to move toward the chimney and
gains a velocity (Fig. 10).Fig. 10. Solar Chimney
Power Plants
so ar c mney co ec or conver s ava a e so ar radiation G onto the collector surface Acoll into heat output.
Collector efficiency ncoll can be expressed as ratio of the
heatoutput of the collector as heated air Q and the solar radiation
G (measured in W/m2) times Acoll[9].
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Collector Efficiency Heat Output
Collector Area
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Spesific heat capacity of the air
The temperature differences
e ween e co ec or an ou ow
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Air speed at collector
outflow/chimney inflowChimne cross-section area
Spesific dendsity of air at temperature To +T at
collector outflow/chimney inflow
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10. Collector Efficiency
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Additionaly valid for heat balance collector:
ective absor tion coefficient of Loss correction value in W/m2K , allowin
the collector for emission and convection loss
Thus collector efficiency can
also be expressed like this:
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ses and ground storage in the collector area neglected.
Typical Values:
= 0.75-0.8
= - 2 =
G=1000 W/m2
T=300C
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11.The Chimney
The efficiency of the chimney (i.e. The conversion of heat
kinetic energy) is particularly independent of the rise of air
perature in the collector; it is essentially determined by the
o .
s solar chimneys can make particularly good use of the low
in air temperature produced by heat emitted by the ground
ng e n g an even e meager so ar ra a on o a co
. Comparing with the collector and turbine, the chimney
ciency is relativelly low, hence the importance of size in its
ciency curve. For example, at a height of 1000 meters,ney efficiency is somewhat greater than 3% [10].
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er air is
lative to
r inside
himney
different from the inside the
chimney.
HC
P(pressure) under the
gravity changes with
res ect to hg. 11 Chimney Height
feratial form g : acceleration due to gravity
nd
HC : Chimney height
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HC
r ens y n e c mney
g. 11 Chimney Height
t of the chimney
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Ptot increases with chimney height.
is consist of two components(dynamic and static)
Ptot =PS+Pd
he static pressure difference drops at the turbine, the dynamic
component describes the kinetic energy of the air flow.
soPS= O Ptot=Pd
Ptot=ptotVC,max AC Efficiency of the chimney can
be establishedvolume
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Actual division of the pressure difference into a static
the turbine. If the turbine is left out, a maximum flow speed
of VC,max is achieved and the whole pressure difference is
use o acce era e e a r.
elli E uation:
0
T Temperature rises between collector inflow and
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his basic simplified explanation one of the basic charesteristic
so ar c mney,w c s t at t e c mney e c ency smentaly dependent only on chimney height. Flow speed and
rature rise in the collector do not come into it.
Thus the power contained in the flow
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12.The Turbine
Turbine in a solar chimney do not work with staged
locity like a free-running wind energy converter, but as a
sed pressure-staged wind turbogenerator, in which, similarly
a hydroelectric power station, static pressure is converted totational ener usin a cased turbine- in this a lication
stalled in a pipe. The energy yield of a cased pressure-staged
rbine of this kind is about eight times greater than that of a
- - .
Air speed before and after the turbine is about the same. The
r unit time and the fall in pressure at the turbine. With a viewmaximum energy yield the aim of the turbine regulation
s em s o max m ze s ro uc un er a o era n
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Blade pitch is adjusted during operation to regulate
.As soon as the wind speed in the chimney exceed 2.5 m/s the
ine is started automaticaly and cut into the public grid. The
ut power of the turbine is adjusted by limiting the rotation
uency of the turbine. This can be adjusted by changing thee an le automaticall Fi . 12 .
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he pressure drop
wt
Powerwt =VC ACPS
ctrical Power W = V I
ume Flow
finally we get the equation
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3. The A ro riate Charesteristic Curve
wt
between these extreme at:
PP=V
PS
.
2/3PtotPs
. 13. Characteristic Curve
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Thus mechanical power taken up by the
owerwt,max = coll c coll
Powerwt,max = (2/3)ncoll(g/CpTo)HoAcollG
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ollector Diameter Dcoll: 2200m
o ar rra a on : m
echanical Efficiency nwt : 0.8
ollector Efficiency ncoll : 0.6
eat Capacity of the Air CP : 1005j/kgKmbient Temperature T0 : 20
0C
ravit Acceleration : 9.81m/s2
ic: (2/3)(0.8x0.6)[9.81/(1005x293)]x750x3751000x1000
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. Typical Dymensions for Solar Chimneys
With Different Power
Power BlockMW 5 30 100 200
With 2300 kWh/m y global radiationymens ons
Collector
Diameter Dcoll
m 1110 2200 3600 4000
Chimney Height
HCm 445 750 950 1500
Chimney
Diameter DC
Annual Energy
ProductionGWh/y 13.9 87.4 305.2 600
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15. Thermodynamics2
Block Size MW 5 30 100
erature rise
ollector
oK 25.6 31.0 35.7
ft Velocity in
mney
ul load)
m/s 9.1 12.6 15.8
l PressurePa 388.3 767.1 1100.5erence
ure Loss by
riction Pa28.6 62.9 80.6
ector n
imney)
ure Drop at Pa314.3 629.1 902.4
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Pressure Loss atPa 40.4 75.1 117.5
verage Annual Efficiency
Collector % 56.24% 54.72%
Chimne % 1.45% 2.33%
52.65%
3.10%
Turbines % 77.00% 78.30% 80.10%
Whole System % 0.63% 1.00% 1.31%
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Power Block Size MW 5 30 100
.
Annual Energy Production
Total GWh/y 13.9 87.4 305.2
Per m2 kWh/m2y 14.4 23.0 30.0
Annual Operating
h/y 8423 8506 8723ours
Full Load Hours h/y 2780 2913 3052
. . .
Night Energy
ProductionGWh/y 1.5 8.7 32.0
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17. Technical Data Quantities
ower Block Size MW 5 30 100
ollector Diameter m 1110 2200 3600
ss Collector Roof-m 162 252 346
tal Covered Area m 76 118 159
Glass Roof Area
Totalm2 967700 3801000 10180000
2x4mmm2 328880 1318000 3570000
Single Glazedm2 61900 2433000 6510000
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lass Roof Area m2 947700 3801000 10080000
Chimney Area m2 4500 11000 20000
lass Roof Height
(external)m 2.0 4.5 6.5
lass Roof Height
(internal )m 10.0 15.5 20.5
Raw Glasskm2 1.3 5.1 13.7
a e. : o ec or a a uan es
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18. Energy Production Costs
With the support of construction companies,he glass industry and turbine manufacturers a rather
ould be compiled. We asked a big utility "Energie in
Baden-Wrttemberg" to determine the energyproduction costs compared to coal- and combinedycle power plants based on equal and common
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Fig. 14. Energy production costs from solar chimneys, coal and
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No ecological harm and no consumption ofsources not even for the construction. Solar chimne s
redominantly consist of concrete and glass which areade from sand and stone plus self-generated energy.
-nd stone solar chimneys can reproduce themselves. Auly sustainable source of energy! [13].
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