Manuscript title :
ANALYSIS AND POSSIBILITY OF SOLAR CHIMNEY POWER
PLANT IMPLEMENTATION ON THE DALMATIAN COAST
Author’s:
Dipl.ing. Sandro Nizetic, research assistant
( CORRESPONDING AUTHOR )
Address: Faculty of Electrical Engineering, Mechanical Engineering and Naval
Architecture, University of Split, R. Boskovica b.b., 21000 Split, CROATIA
mail : snizetic@fesb.hr
phone : 0038521305881
mobil phone : 00385915696607
Fax : 0038521305893
Ph.D. Neven Ninic, full professor
Address: Faculty of Electrical Engineering, Mechanical Engineering and Naval
Architecture, University of Split, R. Boskovica b.b., 21000 Split, CROATIA
mail : nninic@fesb.hr
phone : 0038521305879
Fax : 0038521305893
1
Abstract: This paper analyses the possibility of solar chimney power plant application – as
an environmentally acceptable energy source – in small settlements on the Dalmatian
mainland and islands. The analysis was carried out in two characteristic locations in central
and southern Dalmatia (Split and Dubrovnik). These areas also have the highest solar
irradiation in Croatia. The solar characteristics of the Dalmatian coastal region are shown
together with characteristic meteorological data. The existence of a SC power plant, its
chimney height being 550 m and its collector roof having 1,250 m in diameter would achieve
the mean power of 3.5 MW. The annual SC power plant average electric power production
would range between 7.0 GWh/annum and 9.0 GWh/annum. An approximate analysis of
costs was done together with the estimate of the total investment. The levelized electricity
cost was calculated.
Keywords: Solar chimney, Dalmatia region, Electric output, Levelized electricity cost
2
1. Introduction:
Solar energy is an inexhaustible and, at the same time, environmentally the most
acceptable renewable source of energy. The average annual fall of solar energy as one
square metre of earth would be the equivalent to the burning of 100 litres of heating oil – but
without any of the damaging emissions. Such energy is free of charge and need not be
imported, and most importantly – it does not pollute the environment. Nowadays solar
energy, unfortunately, occupies a smaller portion of the total energy generation and its
utilisation is still insufficient. Due to the ever decreasing amount of conventional (fossil)
fuels, solar energy, being renewable, has become exceedingly important and commercially
more affordable. As a proof of this is the European strategic decision on the application of
clean technologies – which was confirmed by signing the Kyoto Protocol. In the near future,
Europe plans to abandon the fossil technologies and provide for at least half of its energy
needs by the application of renewable energy sources. The Mediterranean countries, Croatia
being among them, have to foresee the greatest possible portion of renewable energy sources
as a basis for their energetic future.
Organized and efficient use of solar energy can only see significant growth by the
implementation of new clean technologies. One such relatively new technology is the solar
chimney power plant (SC), discussed in this paper as a possible electric power source. The
basic SC plant concept was designed by Schlaich [1], together with his partners. Basically,
the SC plant serves for turning the solar energy into work, i.e. the electric power. The plant
main parts are collector roof, solar chimney, and machinery space with turbines and
generators for electric power production. Source of power is working potential of heated air
defined according to [2]. Working potential is concentrated at the bottom of the solar
3
chimney as pressure difference. The difference in pressures relates to the surrounding
atmospheric and the internal heated air at the chimney inlet. The plant chimney intensifies
the buoyancy effect which causes the created difference in pressure to start the turbines,
which generate the electric power.
Croatia is a tourism oriented country with countless natural beauty spots and one
of few countries spared from mass tourism. Croatia annually earns an average of 5.0 billion
euros from tourism, which is also the main revenue and the basis of commerce. Last year,
Croatia was chosen as the most desirable holiday destination in Europe. Each year, an ever
increasing growth in visits and greater interest from the leading EU countries is noted. The
energy needs have increased, so it is extremely important to provide stable energy sources.
Croatian strategic aims are the environment and natural beauty preservation, as well as
energetic stability. In this regard, the application of renewable energy sources imposes itself
as the right choice, considering Croatia has favourable climatic and meteorological
characteristics, i.e. it has significant solar and wind potential.
2. Theory review of solar chimney power plant
On the figure (1) are three basic parts of the SC plant: collector roof, solar
chimney, and turbines with machinery space, which includes the electric power generators.
The physical principle on which the plant operation is based is simple and fundamental. The
relatively colder surrounding air enters along the circumference of the collector roof in the
space below the collector roof. The solar radiation passes through the collector roof (glass or
special foil) and heats the ground under it.
4
Figure (1) Schematic overview of solar tower principle
The air is heated in the collector from the ambient temperature T0 to the air
temperature at the collector outlet Tcoll, which is up to 50 °C at the most, (temperature
growth ∆T=Tcoll-T0,
is usually between 10 and 30 K). The pressure difference
pac (occuring due to different air densities) at the chimney bottom, where the greatest
working potential is concentrated (worked out in detail in [2]), is defined according to the
expression (1), [3]:
pac  g 
Hc
 
at
 c   dz  c gH c
0
5
T
T0
(1)
The total working potential presents the buoyancy force available work, gained
by raising the air from the bottom (z=0) to the total chimney height (z=Hc), where most of
the available work is consumed by the turbine and electric power production.
The role of the plant chimney is to convert the thermal flow brought into the
collector Q by the sun, into the turbine work and kinetic energy (buoyancy effect). The
rewritten expression for the chimney efficiency is defined according to the expression (2),
[1]:
sc 
gH c
C pT0
(2)
The solar tower plant efficiency is low, just a few percentages, however, solar
energy is free, and so the whole investment after all makes sense. In so far the SC plants are
analogue with hydroelectric power plants.
The total plant efficiency is equal to the product of partial efficiency of each plant
component, i.e.:
 sp   sc collt
(3)
According to the expression (2) it can be clearly concluded that the chimney
height Hc has the greatest influence on its efficiency – the higher the chimney, its efficiency
increases. Unfortunately, due to techno-economic reasons the chimney height is limited to
approximately 1000 m. The chimney is the component of greatest influence on the total low
efficiency – which is shown in figure (2), based on the data from [1]. It should be pointed out
6
that the actual thermodynamic efficiency of the chimney is after all considerably greater.
Namely the (little) work produced by the chimney, which is proportional to the numerator in
(2) is a more quality form of energy than the (great) heat taken by the collector (proportional
to the denominator in (2)).
The influence of height to the chimney efficiency is shown in figure (3a), and the
influence of the ambient temperature in figure (3b). The ambient temperature influence on
Efficiency (%)
the produced electric power is little, which has been studied in detail in [4].
90
80
70
60
50
40
30
20
10
0
turbine
collector
chimney
0
overall
10 20 30 40 50 60 70 80 90 100
Pow er of plant (MW)
Figure (2) Influence of SC components on overall efficiency (  sp )
Chimney efficiency,(%)
3,5
3,0
2,5
2,0
1,5
1,0
0,5
0,0
100
300
500
700
Chim ney height Hc, (m )
(3a)
7
900
Chimney efficiency (%)
3,00
2,50
2,00
1,50
1,00
270
280
290
300
Ambient temperature, T0 (K)
(3b)
Figure (3) Influence on solar chimney efficiency: (3a) influence of solar chimney height,
Hc (T0=293K), (3b) influence of ambient temperature T0 (Hc=550 m)
It is interesting to observe that the efficiency of the chimney itself as a thermal
engine, according to (2) does not depend on the air temperature increase ΔT. According to
the efficiency definition, its numerator contains the buoyancy force work up to the chimney
top, while the denominator contains the received heat. The reason for independence from
temperature difference is the proportionality of work and heat of the same temperature
growth ΔT (
gH c
T  C p T ).
T0
The collector, as an important part of the plant has the task of transforming the
overall available sun irradiance G (W/m2), on the collector area Acoll (m2) into useful thermal
 (W). By definition, the collector efficiency is as follows:
flow Q
coll 
Q
AcollG

m C p T
AcollG

8
c  vc  Ac  C p  T
AcollG
(4)
According to [5], and the data from [1] the collector efficiency for a single glass
roof, ΔT and G being given, can be calculated as follows:
 T 
 T 
 coll G, T   13.116
  6.3364
  0.72
 2G 
 2G 
2
coll
(5)
A traditional SC power plant uses axial turbines, where, according to their
features, they can be categorised between wind turbines and gas turbines. The turbine
assembly main task is the efficient power transformation of the part of the available working
potential. The main turbine loss in the SC power plant is the exit kinetic energy (besides the
internal fluid friction loss) where the appropriate turbine efficiency t is defined as follows:
2
t 
Ptc  Plc

Ptc
v
m C p T sc  m c
m C p T sc
2  1
vc2 / 2
C p T sc
(6)
The overall turbine assembly efficiency differs with various authors. According
to the reference, [1], [6] and [7] turbine efficiency varies from 40 up to even 90 % for the
plants of great nominal power. Too high velocities of air flow are not suitable as they
unfavourably influence the turbine efficiency.
The whole SC power plant working regime is the one in which the greatest
produced electric power Pwt . max can be achieved for the given weather conditions. In such a
regime only 2/3 of the turbine theoretical power are allowed, as according to [1] for such a
working regime the mass flow and specific work product per 1 kg of air is the highest. Then,
according to [1] and taking in account blade, transmission and generator loss, included
in wt , Pel can be calculated as follows:
9
2
g
Pel  Pwt . max wt  coll
H c AcollG wt
3
C pTo
(7)
It should be mentioned that, by the extension of plant dimensions Hc and Dcr, the
exit power increases. For various solar chimney height combinations Hc and collector areas
Acoll, the same exit power can be gained.
3. Solar characteristics of Croatia and Dalmatia region
Croatia has a Mediterranean and continental climate. Forty-three weather
stations have recorded solar irradiation averages over the years, having completely covered
the Croatian territory. Most weather stations do not measure the total irradiation or insulation
but the sun shining hours. The Croatian coastal area (the Adriatic coast) is divided into the
northern, central (central Dalmatia) and southern Adriatic (southern Dalmatia). The total sun
irradiation on a horizontal surface in central and southern Dalmatia is registered by 13
weather stations. Table (1) compares the irradiated sun power in various Croatian regions.
Location
in Croatia
Dubrovnik ( south Dalmatia )
Istra (north Adriatic )
Split ( middle Dalmatia )
Slavonija (continental region)
Zagreb (continental region )
Annualy average
kWh/m2day
4.4
3.4
4.2
3.4
3.2
January-average
kWh/m2day
Julay-average
kWh/m2day
1.8
1.2
1.7
1.0
0.9-1.0
7.0
6.0
6.6
6.0
5.7
Table (1) Annual average solar irradiance for different regions of Croatia
(averages for decade), [5]
10
In table (1), we can notice that daily-irradiated sun energy on a horizontal
surface, for the Adriatic has values between 1.2 and 1.8 kWh/m2 in January, and between 6.0
and 7.0 kWh/m2 in July. The great advantage of the climate is in winter months. In January,
the continental part of Croatia receives a double amount of solar energy than northern
Europe. The southern part of Dalmatia receives 3 to 5 times more solar energy than northern
Europe, twice more than central Europe. In the continental part of Croatia there is the annual
average of approximately 1200 kWh/m2, while in the coastal area it exceeds 1600 kWh/m2.
For the optimal surface inclination, the average irradiated amount of sun energy increases for
about 20 % in relation to the data given in table (1). It can be concluded that the difference
between the irradiated amount of sun energy for central and southern Dalmatia is small. The
continental parts of Croatia – e.g. the area of the city of Zagreb – gets up to forty percent less
solar energy (annual average) in comparison with Dalmatia.
In figure (4) are shown monthly mean air temperatures for central Dalmatia. In
January, the daily mean air temperature is 8.8 °C, while in July it is 24.5 °C. In figure (5),
the distribution of the irradiated solar energy (W/m2) on horizontal surface is shown. The
data record a typical day in the hottest (July) and coldest (January) month for the area of
central Dalmatia.
The overall irradiated amount of energy is even up to 70 % greater than in most
parts of central and particularly northern Europe for the optimally inclined surface. For
example, the sunniest parts of the Croatian coast do not fall behind Greece at all. The
sunniest parts of Europe receive only slightly more solar energy ranging from 4 to 8%.
11
The solar irradiation values we will be using further on have been chosen for two
characteristic locations; Split-central Dalmatia and Dubrovnik-southern Dalmatia. The
recorded data regard the following weather stations:
SPLIT – Marjan – WMO* (14445) – Latitude 43° 31’; Longitude 16° 26'
DUBROVNIK – Gorica – WMO (14472) – Latitude 42° 39’; Longitude 18° 5'
The data are according to [8], [9], and [10] and represent 30-year average
measurements by the Croatian Weather Bureau, completed by the Croatian Energetic
Institute ''Hrvoje Požar''.
Average temperature of air, °C
30
25
20
15
10
5
0
1
2
3
4
5
6
7
8
9
10
11
12
Month
Figure (4) Monthly average air temperature for Dalmatia region
_______
* WMO – World Meteorological Organisation
12
Horizontal solar radiation, W/m 2
800
700
Julay
January
600
500
400
300
200
100
0
5-6
6-7
7-8
8-9
9-10 10-11 11-12 12-13 13-14 14-15 15-16 16-17 17-18 18-19
Daily Hours
Figure (5) Daily hourly average radiated energy, W/m2, for
horizontal surface and central Dalmatia region
4. Annual production of electric energy for Dalmatian region
For the calculation of the annual amount of electric power produced by the SC
power plant the following technical features have been adopted:
SC power plant basic technical features:
-
collector roof diameter, Dcr = 1250 m
-
solar chimney height, Hc= 550 m
-
chimney diameter, dc= 82 m
-
distance from the ground to the cover, 2,5 m
-
single glass collector roof
13
-
without additional thermal energy storage
-
chosen temperature difference ΔT from 7 K to 25 K
-
blade, transmission and generator efficiency : wt  0.8
The plant average annual achieved power Pav.an is calculated from the optimal monthly Pj ,
according to the following expression:
 P


j
Pav.an
j
j
(8)
i
i
It is assumed that the optimally achieved monthly powers are those that give the
highest electric power production for the considered month. The conditions for choosing the
optimal power are: constant temperature increase in the collector ΔT and maximum
produced amount of electric power. In figure (6) such calculation of the maximum electric
power production in Split in June for ΔT=15 K ( Popt  Pjune  5215 kW ) is shown.
9000,0
Pel.max= 8000 kW
Electric pwer output, P el (kW)
8000,0
7000,0
6000,0
Popt=5215 kW
5000,0
4000,0
Popt=5215 kW
3000,0
d= 7.8 h
Eel.max=40674 kWh/day
2000,0
1000,0
0,0
5-6
6-7
7-8
8-9
9-10
10-11 11-12 12-13 13-14 14-15 15-16 16-17 17-18 18-19
Hours
 d= 7.8 h
Figure (6) Monthly optimal achieved electric power output Popt (Split, June, ∆T=15K)
14
By this way of monthly calculation, the highest annual electric power output Eel.an is
gained for the achieved ∆T. The optimum air temperature increase ∆Topt is the one with
which there is maximum annual electric power output Eel.an. Further on in economic analysis
this power will be called nominal. The Eel.an calculation results for Split and Dubrovnik are
shown in figure (7).
Produced electric energy,
Eel.an (MWh/y)
9500
9000
8500
8000
7500
7000
Split
6500
Dubrovnik
6000
5
10  Topt
15
20
25
Tem perature difference  T (K)
Figure (7) Annual produced electric energy for central and south Dalmatia region
The highest mean annual electric power output for Split is Eel.max = 9058
MWh/annum for ΔTopt = 11.3 K, while for Dubrovnik it is Eel.max= 9154 MWh/annum for
ΔTopt = 11.5 K. Previously stated values for power and electric power are related to the
average power defined according to the expression (8). The physical reason for the existence
of optimum air temperature increase in the collector ΔTopt is of two kinds. Namely, with very
small ΔT values the collector efficiency is extremely high, but the turbine efficiency is very
low, and vice versa. The reason for the low turbine efficiency lies in high air flow velocities
due to which kinetic energy losses dominate.
15
In the reference [1], the so-called Capacity factor ''f'' is defined. It represents
the ratio between the actual annual number of working hours τs for the given conditions and
the overall annual number of hours τsan, i.e.
f(%) 
s

 s  100
 san 8760
(9)
For the solar tower plant of chosen technical features, a number of working hours was
simulated for the given conditions and chosen locations in Dalmatia. Based on this, factor f
was defined for given conditions. The data are shown in table (2) depending on the achieved
temperature difference ∆T.
T(K)
SPLIT
DUBROVNIK
7
33.9
32.9
10
27.5
27.6
Capacity Factor f (%)
15
20
25.6
24.4
25.4
24.2
25
24.0
23.2
Table (2) Simulation of capacity factor
By the analysis and simulation carried out for the chosen locations in Dalmatia
(Split, Dubrovnik) an average of 5.5 to 8 solar tower plant-working hours per day can be
expected. It has been established that, for the given meteorological conditions and chosen
geographical locations, a SC plant can produce an annual average of electric power between
7.0 and 9.0 GWh, depending on the achieved temperature difference ∆T. Cumulative annual
production of electric power simulated monthly, for Split and ∆T=15°C, is shown in figure
(8).
16
T = 15 K, Location: Split
10000000
Monthly energy production, kWh/m
9000000
8000000
Annual results :
Annual energy production: 8.79 GWh
Operating hours: 2338 h
Capacity factor: 25.6 %
7000000
6000000
5000000
4000000
3000000
2000000
1000000
0
136
287
473
683
919
1153
1388
1604
1796
1970
2108
2238
Operating hours
Figure (8) Simulation example of annual produced electric energy for Dalmatia region
5.0 Economic aspect of produced electric energy
The solar tower plant capital investment consists of the chimney, collector roof, and
turbine assembly building construction costs. The costs structure in relation to the overall
investment is the following: the chimney bears approximately 30 – 50 % of costs, while the
collector roof bears about 20 - 40 %. Medium orientation price for the collector roof made of
single glass amounts to 6.0-9.0 €/m2, while for the chimney made of reinforced concrete, it
amounts to 200-500 €/m2. If the collector roof is produced in special plastic film, an
investment about 30 % lower compared to the traditional glass covering, can be expected.
The turbine assembly costs are more complex to analyse, therefore their portion jumps up
with the decrease of nominated power. For the nominated power of 200 MW, for example,
the overall specific turbine expenses amount 210 €/kWel, while for 5 MW, they amount 1000
17
€/kWel. Besides capital costs, it is necessary to mention the testing and commissioning which
approximately amount 6 - 10 % of the total investment.
The abovementioned costs for solar power plant individual components are for
orientation purposes and depend on the plant nominal power and on particularly designed
collector roof performance. The stated costs include costs of labour.
For the plant of chosen technical features in accordance with chapter (4), based on
the reference [8], an estimate of investment costs was done.
Overall investment:
- collector roof: approx. 9.3 Mio. €
- chimney: approx. 34.7 Mio. €
- turbines: approx. 6.0 Mio. €
- engineering, tests, misc.: 3.5 Mio. €
--------------------------------------------------Total invested capital: K0= 53.5 Mio. €
Average costs of produced electrical energy are calculated according to [3].
kw 
K0
Eel .an
n

fw

 n  1  r 
i 1
i


 rb 

(10)
where factor fw
n

1  p  p
fw 
1  p n  1
18
(11)
Based on the analyses carried out in chapter (4.0) depending on the chosen
temperature difference ∆T, the SC electric power plant annual energy production, Eel.an is as
follows:
For SPLIT
7.26 - 8.93 GWh/per annum
For DUBROVNIK
7.02 - 8.97 GWh/per annum
For the calculation of produced electrical energy price, the necessary
parameters have been established as follows:
- rate of inflation: r = 6.0 % p.a.
- maintenance and repair cost: rb = 2.0 % p.a.
- calculated interest rate: p = 6.0 % p.a.
- period of amortization: n = 20 years
Using previously adopted data and the expressions (10) and (11) the price of
produced electrical energy (€/kWh) can be calculated. The calculation results for the two
characteristic chosen locations, depending on the average annually produced electrical
energy are shown further on:
SPLIT
0.29 - 0.36 €/kWh
DUBROVNIK
0.29 - 0.37 €/kWh
Through the analysis carried out we can conclude that the average price of
electrical energy kWh produced by a SC electric power plant in Dalmatia, would be 0.33
€/kWh.
19
Levelized electricity cost, €/kWh
0,35
0,3
0,25
0,2
0,15
0,1
20
25
30
35
40
45
50
Amortization years
Figure (9) Influence of amortization period on levelized electricity cost
Assuming an amortization period of 40 years, the average levelized electricity
price would be 0.16 €/kWh. The amortization period influence on the mean price of
levelized electricity is shown in figure (9).
Analysis and estimate of costs were done based on the data about prices according to [3] and
[11].
6. Conclusions
For a SC power plant of chosen technical features, an overall technical analysis was
carried out for the purpose of possible application in the electrical energy production for
Dalmatia and Dalmatian islands. The following conclusions may be drawn based on the
analysis carried out:
20

SC electrical power plant of technical features as in chapter (4.0) would produce an
average of 7.0 - 9.0 GWh /per annum in Dalmatia, depending on the achieved air
temperature difference ΔT. The plant nominal power would be 3.5 MW, while the
''peak'' would be reached in July, e.g. 8.1 MW for ΔT=20 K. Annually, an average of
5.72 kWhel/m2annum - 7.36 kWhel/m2annum could be expected per m2 of collector
surface.

The levelized electricity mean price would be 0.33 €/kWh. The present electricity
price in Croatia is 0.1 €/kWh. Obviously, a construction of SC electric power plant in
Dalmatia is not profitable now. Taking into consideration the time still to come and a
broader context of the energy issue overall, here are a few interesting reflections.
a) As already mentioned in the introduction to this paper, the main Croatian revenue
is tourism, which has been growing, year after year. The consequence of this is the
exceeding need for electricity whereby the maximum Croatian need does not come in
winter but in summer (the summer maximum for 2005 began in late July and was
about 2400 MWh/h, while the winter maximum began in early February and was
about 2300 MWh/h). It quite often happens that in summer, due to overloading, the
electric energy system collapses, which is particularly the case on Dalmatian islands
during the holiday season.
b) When Croatia joins the EU we expect a rise of electric energy price of up to 20%
compared to the present market price. For example, the electric energy price in
Germany is 0.15 €/kWh.
c) State subsidies for stimulation and popularisation of renewable energy sources
would lower the levelized electricity price.
21
d) Croatian strategic orientation is preservation of the environment and natural
beauties. This strategic objective can actually be realised by the application of
renewable energy sources in as much as possible.
e) In future, the amounts of fossil fuel will decrease which will finally result in
favourable investment conditions for the application of renewable energy sources.
f) SC electric power plant’s great advantage is its long life of up to 60 years.
Regarding this - in [3] - there is a comparison between the life of a SC electric power
plant and a traditional fossil fuel driven power plant. A conclusion has been made
that, taking a long-term view, the SC electric power plants are much more
favourable. A traditional fossil driven plant has a shorter life, about 20 years on
average (it may be longer, but the maintenance costs jump up with the years), high
maintenance costs, and variable but nowadays most influential fuel costs. In future,
fossil costs will most certainly change their prices in an upward direction only and
after shorter and shorter periods, which does not say much for the traditional plants.
g) The possibility of SC electric plants application in integrated energy systems,
which would additionally lower the levelized electricity price.
Based on the presented reflections and carried out analyses, we can conclude
that at this moment building solar chimney electric power plants in Dalmatia is
profitable over the long term only. If, however, the previously presented facts and
conclusions are acknowledged, the building of such electric power plants becomes a
serious and likely option.
22
Nomenclature:
Ac
Cross sectional area of solar chimney, m2
Acoll
Solar collector area, m2
Cp
Specific heat capacity of air, kJ/kg°C
Dcr
Diameter of collector roof, m
dc
Diameter of chimney, m
dz
Differential element of chimney height, m
Eel.an
Annual produced electric energy, MWh/y
Eel.max Maximum annual produced electric energy, MWh/y
f
Capacity factor
g
Acceleration of gravity, m/s2
G
Solar irradiance, W/m2
Hc
Solar chimney height, m
i
Years
kw
Levelized electricity cost, €/kWh
K0
Total invested capital, Mio. €

m
Mass flow rate of air, kg/s
n
Amortization period, years
p
Calculated interest rate, % p.a.
Pav.an
Average annual electric output from the solar chimney, kW
Popt
Optimal average electric output from the solar chimney, kW
Pel
Electric output from the solar chimney, kW
Pel.max
Maximum electric output, kW
23
Pj
Average monthly electric output, kW
Plc
Power loss due to exit kinetic energy, kW
Ptc
Power of theoretical air cycle, kW
Pwt.max Maximum mechanical power taken up by the turbine, kW
r
Rate of inflation, % p.a.
rb
Maintenance and repair cost, % p.a.
Q
Heat gain of the air in the collector, kW
T0
Ambient temperature, K
Tcoll
Temperature of air at collector outlet, K
vc
Inlet air velocity of solar chimney, m/s
z
Level from the ground, m
24
Greek symbols:
coll
Solar collector efficiency
sc
Solar chimney efficiency
 sp
Overall efficiency
t
Turbine efficiency
 wt
Blade, transmission and generator efficiency
 at
Density of ambient air, kg/m3
c
Density of air at inlet in solar chimney, kg/m3
d
Daily working hours of solar chimney power plant, h/day
j
Monthly working hours of solar chimney power plant, h/month
s
Working hours of solar chimney power plant, h/year

i
Total working hours of solar chimney plant for optimal electric output, h/year
i
pac Pressure difference produced between chimney base and the surroundings, Pa
T
Temperature rise between collector inflow and outflow, °C
Topt Optimum temperature rise between collector inflow and outflow, °C
25
References:
[1] Sclaich J. The solar chimney: Electricity from the sun. In: Maurer C, editor.
Germany: Geislingen; 1995.
[2] Ninić N. Available energy of the air in solar chimneys and the possibility of its
ground level concentration. Solar Energy 2006 (Article in press).
[3] Sclaich J, Bergermann R, Schiel W, Weinrebe G. Desing of commercial solar
updraft systems-Utilization of solar induced convective flows for power generation.
Germany: Stuttgart; 2004. (unreleased text)
[4] Y.J.Dai, H.B. Huang, R.z. Wang N. Case study of solar chimney power plants in
North-western regions of China. Renewable Energy 2003; 28: 1295-1304
[5] Group of authors. SUNEN, Croatian Energetic Institute ''Hrvoje Požar''; 1997
[6] Backstrom T.W., Ganon A.J. Solar chimney turbine characteristics. Solar Energy
2004; 76: 235-241
[7] Haff W. Part II: Preliminary test results from the Manzanares pilot plant.
International Journal of Solar Energy 1983; 2:141-161
26
[8]
Z. Matić, ''Solar radiation in Republic of Croatia'', Croatian Energetic Institute
''Hrvoje Požar''.Croatia: Zagreb; 2005.
[9] Climate and solar characteristic of Croatia. Meteorological and Hydrological
service of Croatia
[10] Actual real-time measured data, Meteo-ocean station ''Punta Jurana'', Institute of
Oceanography and Fishers, Split, Croatia
[11] Haff W, Friedrich K, Mayr G, Sclaich J. Solar chimneys: Part I: Principle and
construction of the pilot plant in Manzanares. International Journal of Solar Energy
1983; 2(1):3-20
27
Figure Captions:
Figure (1) Schematic overview of solar tower principle
Figure (2) Influence of SC components on overall efficiency (  sp )
Figure (3) Influence on solar chimney efficiency: (3a) influence of solar chimney height,
Hc (T0=293K), (3b) influence of ambient temperature T0 (Hc=550 m)
Figure (4) Monthly average air temperature for Dalmatia region
Figure (5) Daily hourly average radiated energy, W/m2
horizontal surface and central Dalmatia region
Figure (6) Monthly optimal achieved electric power output Popt (Split, June, ∆T=15K)
Figure (7) Annual produced electric energy for central and south Dalmatia region
Figure (8) Simulation example of annual produced electric energy for Dalmatia region
Figure (9) Influence of amortization period on levelized electricity cost
28
Tables:
Location
in Croatia
Dubrovnik ( south Dalmatia )
Istra (north Adriatic )
Split ( middle Dalmatia )
Slavonija (continental region)
Zagreb (continental region )
Annualy average
kWh/m2day
4.4
3.4
4.2
3.4
3.2
January-average
kWh/m2day
Julay-average
kWh/m2day
1.8
1.2
1.7
1.0
0.9-1.0
7.0
6.0
6.6
6.0
5.7
Table (1) Annual average solar irradiance for different regions of Croatia
(averages for decade), [5]
29
T(K)
SPLIT
DUBROVNIK
7
33.9
32.9
10
27.5
27.6
Capacity Factor f (%)
15
20
25.6
24.4
25.4
24.2
Table (2) Simulation of capacity factor
30
25
24.0
23.2