Types of heat generation in Ukraine in 2016 and their cost
Январь 31st, 2016
• The solar radiation field:
In the estimation of the solar radiation we used the models reported in the "Atlas solaire d’Algerie” [2]. The global solar radiation is the sum of a direct and a diffuse radiation. A critical report on the capderou work showed that if the direct radiation is underestimated the diffuse radiation for a mean day is quite surestimated compared to measured values. All the equations used to estimate the direct and diffuse radiations for any site and given day can be found in reference [1].
dT 
f (i) 
dt 
dT 
p(i) 
dt 
— a(p(i) Tf (i)) )(f (i) Tf (i1)) — C(Tf (i) — Tp(i) ) dTp(i) — Ta )+ e’It 
HeAs V with a — e , b — — 
p(i) 
(1) (2) 
C 
f 
Ax P LAcs ЬХ 
,C 
HeAs, d — ^L^ 
C 
C 
and e — 
FAc (та) 
C 
The energy balance over the flat solar collector leads to the following system of equations solved by the 4th order RungeKutta method.
(Tf and Tp are the fluid and the collector absorber temperatures respectively)
• The ejector flow loop:
• entrainment ratio ra :
(3) 
ra— 
m 
m 
The entrainment ratio is equal to the ratio of the secondary and the driving mass flowrates.
(4) 
with m’ : driving mass flow rate and m’’ : secondary mass flow rate The optimal ratio for any working fluid is given by the following equation [2] :
( pe Л 
( pc Л 

ra — 
3.7 • 
PC 
— 0.507 
l PB ) 
0.85 
SHAPE * MERGEFORMAT
The refrigerant flow loop: Coefficients of performance : COP = — 
OQJd*eaal_________ 
Qbo> + Wp T 
T — T C__ XTB TC 
T — T TH TC 
B 
(5) (5) (7) 
Фcool — m"(h6 — hs) 
Qe 
The installation of the plant and the first two years of scientific monitoring were funded by the European Commission (DG TREN) and the federal state of BadenWurttemberg. In 2004 the monitoring and some technical improvements are funded by the German Government as one of the demonstrations projects within the IEA Task 25 "Solar air conditioning of buildings”.
2. Literature
/1/ T. Erpenbeck, Sorptionsgestutzte solare Klimatisierung. Universitat Karlsruhe; Fakultat fur Architektur. Dissertation. 1999.
/2/ M. G. F. Motta; Thermodynamic design and optimisation of solar assisted desiccant cooling cycles for Italian climates. Doktorarbeit, Universita di Genova, 2002.
/3/ U. Schurger. Teststand fur Sorptionsrotoren — Erkenntnisse und Auswertungen. Tagungsband des 13. Symposium Thermische Solarenergie, Otti, Bad Staffelstein, S.236 — 241,2003.
/4/ A. Kodama, W. Jin, M. Goto, T. Hirose, M. Pons, Entropic analysis of adsorption open cycles for air conditioning. Part 2: interpretation of experimental data. Int. Journal of Energy Research, 24: 263 — 278, 2000.
/5/ A. Kodama, T. Hirayama, M. Goto, T. Hirose, R. E. Critoph, The use of psychrometric charts for the optimisation of a thermal swing desiccant wheel. Applied Thermal Engineering, 21: 1657 — 1674, 2001.
/6/ W. Jin, A. Kodama, M. Goto, T. Hirose, An adsorptive desiccant cooling using honeycomb rotor dehumidifier. Journal of Chemical Engineering of Japan, 31: 706 — 713, 1998.
/7/ A. Kodama, K. Andou, M. Goto, T. Hirose; Performance of an adsorptive desiccant cooling process equipped with double stage dehumidification. Proceedings of the Int. Sorption Heat Pump Conference. S.
425 — 430, Shanghai, China, September 2002.
/8/ U. Eicker. Solare Technologien fur Gebaude, B. G. Teubner Verlag, Stuttgart/ Leipzig/ Wiesbaden, 2001. /9/ U. Franzke, G. Heinrich (Hrsg.). Sorptionsgestutzte Klimatisierung: Entfeuchtung und DEC in der Klima — Kalte — Technik. C. F. Muller Verlag, Heidelberg, 1997.
/10/ HansMartin Henning (Ed.). Solar — Assisted Air — Conditioning in Buildings. Springer Wien New York 2004.
/11/ C. Hindenburg, H.M. Henning, G. Schmitz. Einsatz von Solarluftkollektoren in sorptionsgestutzten Klimatisierungssystemen, Achtes Symposium thermische Solarenergie; OTTI, Staffelstein; Mai 1998.
/12/ C. Hindenburg, L. Schnabel, T. Geucke, M. Motta. First thermally solar autonomous air conditioning system in Germany — Simulations, operation experience and economic aspects. Proceedings of the ISES Conference, Gothenborg/Sweden, June 2003.
/13/ Deutsches Institut fur Normung DIN 1946 Teil 2: Raumlufttechnik/ Gesundheitstechnische Anforderungen (VDILuftungsregeln), Beuth — Verlag 1994.
/14/ J. Pfafferott, S. Herkel, A. Wagner. Sommer 2003: Mussen unsere Burogebaude klimatisiert werden? HLH 55 (2004)
/15/ L. Schnabel. Betriebsanalyse und Simulation einer offenen sorptionsgestutzten Klimatisierungsanlage. Diplomarbeit. Technische Universitat Berlin. 12/ 2003.
No special window frame was applied for these measurements, other than explained in the variants below, see table 2. The reference opening was not covered with a glass plane; this facilitated the experimental setup and would still give interreflection problems when a coloured glass or translucent glass plane was inserted. When the transition zone consists is situated in or directly on the glass, only absorption and diffraction are possible methods to reduce the luminance ratios. Diffraction is not so suitable as it has the same absorptive effect for a direct view through the window, and the diffracted rays next to the left and right side of the window can be very irritating. Diffraction is in general used for highly positioned windows where the diffracted rays give extra light deeper into the office room.
Position Method 
transition zone : absorption on or in the glass plane 
Realisation empty coloured glass 
patterns in transparent glass (dots, stripes, etc.) 
reflection diffraction reflection 
X X 
not possible same effect as absorption lamellas 
transition zone in front of the window opening 
translucent glass 
b 
SHAPE * MERGEFORMAT
The presence of the hybrid PV/T system inside a window makes it highly visible from the exterior as well as the interior. One of the basic ideas behind the design was to express the building integrated solar energy system architecturally in an attractive, maximally exposed way. Conceptually, the window is the traditional solar collector, hence an interesting starting point for integrating other solar technologies.
Figure 3: Illustration of the initial design of the Solar Window building integrated 
Other aesthetical considerations are mainly due to the reflectors. The curved concentrating geometry is decorative and expresses the capturing nature of a solar energy system. The backside facing the interior could be covered with any surface material suitable for the interior context. The modular nature of the reflectors, with no connection to the energy distribution, makes it possible to exchange them for alternative surface, thickness or reflecting geometry. The concave front facing the window will be highly visible from the exterior, and the mirror like surface might be the most critical aesthetical property for a wider acceptance. However, the curved mirror can generate interesting optical expressions in the fagade.
The extruded picture of the PV/T absorber is visible when the spectator is within the optical acceptance angle range, which means that the impression of the individual modules will differ much in height on a short distance. The overall impression of the fagade will hence change when approaching it. The mobility of the reflectors also contributes to a dynamic fagade expression.
The system is initially intended for experimental integration into a low energy, single family house, designed simultaneously with the concept for the solar window, see figure 2. This house has an 18 m2 south facing window structure prepared for the integration of the Solar Window system. The house is constructed with an EPS module system with integrated loadbearing wooden beams, with no thermal bridges. A central brick wall and a ceramic clad concrete floor absorb passive gains. The solar heating system is complemented by a pellet burner, and the PV system is grid — connected while also carrying a local DC circuit for reducing magnetic fields and eliminating losses in battery eliminators, used for DC powered devices.
Consider steady state operation of a solar chimney power plant. The solar collector consists of a transparent deck over a floor that receives solar energy. The collector floor
transfers energy to the air flowing over it at the same rate at which it receives energy from the sun, namely at a G Acoll, where a is the effective absorption coefficient of the collector. The air in the collector loses heat through the collector deck at the same rate that the collector deck loses heat to the environment, namely at pATAcoll, where p is an adjusted heat transfer coefficient that allows for radiation and convection losses and the fact that the temperature difference between deck and environment increases from 0 at the outer edge of the collector to AT at the chimney entrance. The real situation is more complex, but this simple model employed by Schlaich (1995) may be used to derive an approximate expression for the collector temperature rise and the exponent m of the analysis above. Find the air temperature rise by equating energy entering and leaving the collector:
Qfloor — Qdeck — Qcfe
a G Acoll PAT Acoll V pcollcpAT
(11) 
AT —___ a G Acoll____
V pcollcp + P Acoll
If the ambient temperature at ground height is T0, the collector exit (chimney inlet) density is pcoll and assuming parallel temperature profiles inside and outside the chimney a chimney of height Hc will generate a hydrostatic pressure potential, pp:
AT
pp — pcoll g Hc
1 0
pcoll g Hc____ a G Acoll (12)
T0 V pcollcp + в Acoll
This equation is of the form: pp — 
C1 
C2 V + C3 
(13) 
It can be shown that for a relationship of the form p = A Vm, m depends only on the local value of the function and the local value of its gradient, and is given by:
m — 
dpp pp
“dV V (14)
For a function of another form, for example Eq. (13), an equivalent m can be calculated at any point, since m depends only on the coordinates of the point and its local gradient:
— dpp V
dV pp
‘ C1C2
(2 V + C3 )2
V(c2 V + C3)
C2V
(2 V + C3;
Back substitute for C2 and C3 and multiply the denominator and numerator by AT:
V p collc p AT
m = _
(V p coiicp AT + p Aeon AT) = _ V pcollCpAT a G A coll
Qfloor Q 
deck 
Q 
ncfe 
floor 
(16) 
= _ a G A coll _ в A coll AT a G Acoll
Here ncfe is the net rate at which heat is absorbed by the air between the inlet and exit of the collector, expressed as fraction of the rate of heat transfer from the floor to the air. We shall call it the collector floortoexit efficiency since it is a measure of how efficiently the collector transfers heat from its floor to the air leaving the collector. Schlaich (1995) writes the standard collector efficiency for his collector model as:
PAT (17)
ncoll =«_ g
The collector transfer efficiency can be written similarly by dividing out aGAcoll in Eq. (16):
ncfe 1 
PAT
aG
= n coll (18)
a
It is remarkable that in the case of the simplified solar chimney collector model, the exponent m turns out to be simply the negative of the collector floortoexit efficiency. The immediate implications are the following:
• m must have a value between 0 and 1
• for n = 2, the optimum pt/pp is between 2/3 and 1
• the optimal pt/pp ratio is 2/3 only if the collector efficiency equals zero.
Two models have been designed: one system includes evacuated tube solar collector and the other includes doubleglazed flat plate solar collector. Each model is simulated with different insulation thickness and size of overhang and wing walls. The simulation has been performed to select the optimum collector area and slope, generator temperature so that the maximum possible solar heat is gained, and to select the suitable insulation thickness and overhang and wing walls so that minimum possible cooling load is obtained. As seen from figure 2, Nicosia needs air conditioning for 9 months from March to November. Figure 3 shows cooling load of the building in Assab and from the figure it can be seen that air conditioning is needed all year round.
Figure2. Cooling load (kJ) (Nicosia). 
Figure 3. Cooling load (kJ) (Assab) 
80 82 84 86 88 90 92 94 hot water inlet temperature (C) Figure 4. Effect of hot water temperature on solar fraction. 
For Assab the maximum solar fraction is obtained at the optimum generator hot water inlet temperature of 86°C for the system with evacuated tube solar collector. The corresponding figure for doubleglazed flat plate solar collector is 85°C [10]. The cooling water temperature is assumed low enough so that the system works at low generator temperature. Figure 4 shows the generator hot water temperature for Nicosia and the result shows that the optimum temperatures are 86°C and 83°C respectively. The solar fraction is defined as the percentage of the solar energy supplied to the absorption chiller over the total energy supplied (from solar energy and auxiliary heater) to the chiller. When the hot water temperature increases the additional energy is delivered from the heater, which reduces the solar fraction.
Solar heat gain from the collector varies with slope of the collector and latitude. It is proportional to the angle between the collector surface and the incident ray from the sun. For Assab the maximum is obtained at a collector slope of 13° for both types of collectors
[10]
Figure 5. Effect of collector slope on solar fraction 
SLFR EVC — SLFR DGC — SYEFF EVC SYEFFDGC 
. For Nicosia a maximum heat is gained when the evacuated tube collector slope is 25° and the doubleglazed flat plate collector slope is 24° (Figure 5).
The effect of both collector area and storage tank volume on solar fraction (SLFR) and system efficiency (SYEFF) for evacuated tube and doubleglazed collectors are shown in
figures 6 and 7 respectively. System efficiency is defined as the percentage of the incident solar energy converted into cooling effect. For the case of Assab it is given in [10]. As seen from the figures the solar fraction always increases with solar collector size and storage tank volume. In the case of collector area the increase is higher at the smaller collector area, but decreases its increment as the area increases. For the case of storage tank the variation is high at high volume.
Figure 6. Effect of evacuated tube solar collector (ESC) area on solar fraction and system efficiency (Nicosia). 
collector area Figure 7. Effect of doubleglazed flat plate solar collector (DGC) area on solar fraction and system efficiency (Nicosia). 
1 SLFR 1 SYEFF 2SLFR 2 SYEFF 3SLFR 3SYEFF 4 SLFR 4 SYEFF 5 SLFR 5 SYEFF 
1 SLFR 1 SYEFF 1.5 SLFR 1.5 SYEFF 2SLFR 2 SYEFF 3 SLFR 3 SYEFF 
Figures 610 show the effect of collector area and storage tank volume on solar fraction and system efficiency for the insulated building.
The effect of solar collector area on solar fraction and system efficiency for the 2.0m3 hot water storage tank is shown for Nicosia (Figure 8) and for Assab (Figure 9). From the figure it can be seen that the solar fraction of Assab is smaller than that of Nicosia, but the system efficiency is higher. In all cases solar fraction increases with collector area. The maximum system efficiency of the evacuated tube solar collector for both locations is obtained when the collector area is 20m2. For Nicosia the maximum system efficiency is obtained when the doubleglazed collector is 20 m2 while for Assab when it is 30 m2.
The effect of thermal storage tank to the solar fraction and system efficiency is very small comparing to that of the solar collector (Figure 10).
20 10 0
3
storage tank volume (m3)
Figure 10. Effect of storage tank on solar fraction and system efficiency (Nicosia).
Figure 11. Effect of insulation thickness on cooling load. 
Figure 11 shows the effect of insulation thickness on cooling load for both locations. The highest cooling load is obtained when the building is not insulated and the lowest is obtained when the insulation thickness is 0.20 m. The maximum cooling load for Assab is 265 MJ while for Nicosia it is 78.6MJ. The reduction of cooling load in the first 0.05m insulation thickness is 34% for Assab and 25% for Nicosia. For the second 0.05m insulation thickness the reduction drops to 6.2% for Assab and 2% for Nicosia. As the thickness increases the effect of reduction decreases and is insignificant for insulation thickness greater than 0.2m.
overhang and wing wall (m) Figure 12. Effect of overhang and wing wall on cooling load. 
Overhang and wing wall reduce cooling load since the direct solar radiation is prevented from entering the building. As the size increases the reduction also increases (Figure 12). But the effect is very small when compared with the effect of insulation. In the first 0.5 m overhang and wing wall addition the reduction is 4% for Assab and 5% for Nicosia. When another 0.5 m is added the reduction is 2.8% and 2.6% respectively.
Figure 13. Effect of insulation thickness on solar fraction and system efficiency load (Nicosia). 
Figure 13 shows that solar fraction increases with insulation. This is due to the fact that energy demand decreases with insulation. But the system efficiency more or less remains the same.
Conclusion
A TRNSYS simulation model of solarassisted air conditioning system has been developed to simulate longterm performance of buildings in Assab, Eritrea and Nicosia, Cyprus. Two collectors types: evacuated tube collector and doubleglazed flat plate collectors are used for comparison purposes. The model was used to perform a parametric study of the system to investigate the effect of collector area, storage tank size and generator temperature on solar fraction and over all system efficiency. The model was also used to analyze the possibility of reducing cooling by means of addition of insulation, overhang and wing walls to the buildings.
In both locations the highest system efficiency was obtained from the system, which used an evacuated solar collector. For Assab it is 1.85 times greater than that of the system, which used doubleglazed collector and for Nicosia the figure is 1.72.
The lowest cooling load is obtained for both locations when the insulation thickness is 0.20 m and the size of the overhung is 1.5 m. Further reduction could be obtained without economic advantage. Reduction of cooling load is not enough when optimum condition is needed. In addition to the cooling load reduction analysis of the overall cost of the system is important. But for economic comparison the cost of equipment, building materials and fuel oil used in the systems are not the same in all locations.
Seonghwan YOON, Yasunobu ASHIE and Toshio ABE
Building Research Institute, 1 Tachihara, Tsukuba, Ibaragi, 3050802 JAPAN
Introduction: There have been a number of studies on the passive cooling of the outer surface of buildings for the purpose of conserving energy without resorting to fossil fuels, and simultaneously, improving the indoor thermal comfort. In addition to this, the heat island phenomenon has been regarded as a problem (Ichinose et al., 1999). Thus, it is necessary to strive to reduce the thermal load of buildings on the urban environment. It is particularly important to examine thermal properties of finishing materials on the rooftop surface where the incoming direct solar radiation is great. For this reason, the purpose of this study is to examine the cooling effects by the evaporation and the reflection of solar radiation on the rooftop surface by conducting outdoor experiment and numerical calculation. In the outdoor experiment, various test pieces were installed on an existing rooftop to examine the change in the surface temperature on a clear, summer day. Next, numerical calculation was carried out assuming different states of insulation to clarify the influence of rooftop surface cooling on the thermal load both indoors and outdoors in summertime.
Preliminary experiments are done in the daylight chamber of the university of Delft in order to make an estimation of the size of the illuminance in underground spaces. The artificial sky simulates a CIEovercast sky. The illuminance Ehorf in the daylight chamber is 6800 lux. Experiments are done with scale models of scale 1:20 because the height below ground level in the daylight chamber is only 0,8 m in reality (fig. 1). The dimensions of the standard underground space was taken to be 4 x 4 x 4 m3 with a tube of 1 x 1 x 3 m3 on scale.
Figure 2 shows this standard space and the different variants of which the level of illuminance has been tested. The dimensions of the cylindric model (H) and the half sphere
(I) are chosen in a way that the surface of the walls is the same as in the standard model.
All scale models of the underground space are made of white foam, so that internal reflections are taken into account. The inside material of the tube was a material of high specularity in order to send as much daylight as possible to the underground space.
The effects on the illuminance in relation to the dimensions and the form of the space and the tube are investigated. The illuminance is measured at different points on the floor and the wall. On the floor the distance between the grid points was 0,5 m on scale (fig.3). On the wall there were two rows of measurement points: one row on 1,5 m and one on 3 m height, with distance of 0,6 m between the points (fig. 4).
Table 1 and 2 show the results of the measurements. On the floor almost all the models show illuminances between 150 lux and 450 lux and on the wall illuminances between 80 lux and 180 lux. Raising the height of the space or the tube reduced the illuminance in the space, but raising the height of the tube has the most impact. From the symmetries of the spaces it can be concluded that the measurement uncertainty is below 10 lux.
The measured illuminances are too low for offices and livings, but these buildings are yet forbidden below ground level by the building norms in the Netherlands. But exposition spaces can be built underground. Illuminances of 150 lux on walls are very well suited to expose paintings, and illuminances of 300 lux — 450 lux on the floor are suited to show 3D art objects like statues [2,3].
fig. 1. Measurements below ground level in the daylight chamber.
A. Standard 
Ci^£aceJieic]hU5m 
E. Space length 6m 
F. Space length 8m (1 tube) 
D. Space height 6m 
Bi^£acejieic]ht_3m 
SHAPE * MERGEFORMAT
fig.2. Different shapes of the scale models used in the daylight chamber.
0,5 m
fig.3. The gridpoints on the floor of the underground space, distance 0,5 m (scale 1:20).
3 m
1,5 m
0,6 m
fig.4. The gridpoints on the wall of the underground space, distance 0,6 m (scale 1:20).
table 1. Illuminances on the floor of the underground space for the different variants.
lux 
1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
11 
12 
13 
14 
15 
16 
A 
260 
250 
225 
190 
252 
243 
219 
189 
229 
223 
200 
174 
197 
190 
172 
152 
B 
370 
358 
305 
235 
352 
337 
295 
228 
300 
291 
255 
204 
243 
242 
215 
182 
C 
200 
195 
183 
162 
197 
193 
181 
162 
190 
184 
173 
155 
179 
174 
161 
144 
D 
161 
157 
150 
141 
160 
156 
150 
141 
154 
152 
146 
139 
148 
144 
140 
128 
E 
222 
217 
195 
158 
219 
213 
193 
157 
203 
198 
178 
149 
180 
177 
159 
135 
F 
204 
198 
178 
141 
201 
196 
176 
140 
188 
183 
166 
133 
169 
166 
149 
123 
G 
221 
219 
243 
265 
219 
218 
240 
261 
210 
208 
232 
248 
193 
192 
205 
220 
H 
249 
241 
218 
188 
242 
233 
214 
178 
227 
219 
197 
169 
201 
197 
179 
162 
I 
436 
396 
290 
226 
426 
404 
309 
245 
350 
328 
260 
218 
279 
267 
230 
192 
J 
381 
370 
342 
293 
383 
369 
342 
296 
366 
357 
326 
293 
343 
335 
306 
279 
K 
196 
183 
155 
130 
181 
170 
149 
123 
151 
146 
127 
108 
134 
131 
117 
95 
L 
251 
245 
221 
189 
249 
240 
219 
186 
229 
211 
223 
176 
202 
198 
180 
157 
M 
259 
250 
226 
189 
255 
246 
223 
189 
234 
227 
208 
178 
212 
207 
187 
159 
N 
260 
251 
230 
195 
256 
247 
225 
194 
235 
228 
208 
183 
210 
206 
196 
168 
O 
265 
258 
229 
203 
259 
253 
229 
199 
239 
228 
212 
189 
213 
205 
197 
165 
table 2. Illuminances on the wall of the underground space for the different variants.
lux 
1 
2 
3 
4 
5 
6 
A 
169 
167 
154 
132 
128 
116 
B 
185 
173 
151 

C 
150 
139 
123 
130 
129 
122 
D 
123 
123 
116 
107 
108 
104 
E 
137 
131 
116 
98 
97 
85 
F 
118 
112 
95 
86 
84 
75 
G 
160 
160 
169 
129 
132 
141 
H 
161 
123 

I 
163 

J 
196 
181 
162 
141 
135 
128 
K 
147 
141 
132 
132 
130 
121 
L 
165 
160 
144 
128 
125 
110 
M 
167 
165 
155 
130 
126 
116 
N 
168 
167 
154 
132 
125 
114 
O 
172 
170 
151 
143 
136 
128 
Figure 8: Notation system of the SkylightDimensioning Method 
This existing method can be applied to determine the minimal necessary area of transparent surfaces of those skylights that are effected by the hole hemisphere (that "can see” the whole hemisphere).
Ff represents the necessary transparent area of the skylight, it can be calculated with the following equation:
{2} 
eaverage a • b m2
100 Tg — Ts Td ■ ka ■ ^
Nomination of the initial coefficients and parameters:
e average a, b,h r Pc, Pw, Pf 
p, q,m Pa 
a 
: the average illumination coefficient [%],
: the main dimensions — width, depth, height — of the interior space [m],
: the distance between the reference plane and the floor level [m],
: the average reflection coefficients of the surfaces — ceiling, walls, floor — of the interior space [%],
: the main dimensions — width, depth, height — of the lightwell [m],
: the average reflection coefficient of the internal surface of the lightwell [%],
: skylight transmittance modification coefficients: rg — transmittance, rs — obstruction and rd — dirt coefficients [].
: the efficiency of the lightwell [],
: the efficiency of the internal space [].
Calculation and determination of values of the initial coefficients and parameters:
eaverage : the required illumination coefficient, which can be determined using
standards and tables or preliminary recommendations, or it also can be calculated using the En interior (function) specific nominal illumination:
eaverage = EE^ 100%]. {3}
Ekm
Tg, rs, rd : the Tg — transmittance, rs — obstruction and rd — dirt modification values of the
transparent surfaces of the skylight can be determined using existing standards and tables according to the type of the applied — glazing, — structure or depending on the actual environment, for instance:
Tg 
As 
*d 

simple, clear glazing 
0.9 
structural glazing 
1 
countryside, regular cleaning 
0.8 
double, clear glazing 
0.8 
metal structure 
0.9 
countryside, accidental cln. 
0.55 
simple wiregazing 
0.77 
timber structure 
0.8 
residential, regular cleaning 
0.7 
double wiregazing 
0.63 
RC structure 
0.8 
residential, accidental clean. 
0.4 
plastics 
0.8 
industrial, regular cleaning 
0.55 

industrial, accidental cleaning 
0.25 

clean state at handover 
1 
Table 2: Approximate Transmittance, Obstruction and Dirt modification values 
a 
: the efficiency of lightwell, that can be determined using the following equation, where i is the lightwell index and pa is the average reflection value of the internal surface of the lightwell:
i = m(p + q)
2 • p ■ q
The value of ka can be determined using the lightwell efficiency table bellow:
kr 
kr 
{5} 
a ■ b (a + b)(h — r) 
: the interior coefficient can be calculated using the following equation:
П 
: the efficiency of the interior can be determined with the help of the following table (the kr interior coefficient values and the actual pc — ceiling, pw — wall and pf — floor average reflection coefficients shall be also substituted to the table):
pf 
0,3 
0,1 

Pc 
0,8 
0,5 
0,8 
0,5 
0,3 

Pw 
0,8 
0,5 
0,3 
0,5 
0,3 
0,3 
0,5 
0,3 
0,3 
kr 

0,6 
0,63 
0,39 
0,33 
0,39 
0,33 
0,34 
0,37 
0,33 
0,32 
0,8 
0,76 
0,53 
0,45 
0,51 
0,45 
0,45 
0,50 
0,45 
0,44 
1 
0,88 
0,62 
0,54 
0,60 
0,54 
0,53 
0,58 
0,53 
0,50 
1,25 
0,95 
0,71 
0,63 
0,68 
0,62 
0,62 
0,66 
0,60 
0,60 
1,5 
1,02 
0,78 
0,70 
0,76 
0,69 
0,68 
0,72 
0,68 
0,66 
2 
1,1 
0,89 
0,81 
0,85 
0,78 
0,77 
0,80 
0,77 
0,74 
2,5 
1,14 
0,96 
0,88 
0,91 
0,85 
0,83 
0,85 
0,82 
0,80 
3 
1,17 
1,01 
0,94 
0,95 
0,89 
0,87 
0,88 
0,86 
0,84 
4 
1,21 
1,07 
1,01 
1,00 
0,95 
0,92 
0,93 
0,90 
0,89 
5 
1,23 
1,12 
1,06 
1,03 
0,98 
0,95 
0,96 
0,93 
0,92 
In a recent U. S. regional power plan discussion document (North West Council, 2002) the cost of a 400 MWe pulverised coal plant was found to be $1468/kWe in the North West USA. This plant is used as a coal cost baseline for comparison costings against two CLFR/cavern scenarios, one with 54% capacity factor and one with 68%. In Table 1, the coal plant is given an 80% capacity factor, within the normal range for capacity factors in the USA. David and Herzog (2003), for example, use 75% in a study of carbon sequestration. The coal plant IRR was held to 14%, assumed as a reasonable payback for solar plants in NREL (2003), by adjusting the wholesale price for electricity. premium charged for peaking sales, because as the capacity factor is reduced, there is a greater opportunity to indulge in ‘peak lopping’, giving a higher return per kWhe. The IRR for such trading can only be determined using a complex grid pricing model not available to the authors.
Annual Output MW(th) 
14,038,462 
3,620,800 
4,526,000 
Thermal to Electrical efficiency 
39.0% 
31.5% 
31.5% 
Online Status 
0.98 
0.98 
0.98 
Total Annual Equivalent MWH Output 
2,522,880 
1,117,741 
1,397,176 
Annual Gross Plant Revenue US$ 
111,315,773 
45,291,605 
56,614,506 
Coal cost 0.71 MMBTU 
42, 
522 
644 
— 
— 

Reflector Array Cleaning 
— 
3, 
587, 
,143 
4, 
483 
929 

Operations and Maintenance 
15, 
646 
080 
2, 
022, 
,019 
3, 
,159 
,404 
Debt Payment 
28, 
,146, 
027 
20, 
522, 
963 
24, 
359 
,041 
Annual Gross Costs of Service US$ 
58, 
,168, 
724 
26, 
,132, 
,125 
32, 
О о го 
373 
Annual Net Plant Revenue US$ 53,147,049 19,159,481 24,612,133


Table 1. Costs and IRR of coal and CLFR systems 
The solar plants were then evaluated on this selling price and it was found that their IRR is comparable to coal; slightly higher than coal for the 68% capacity factor plant and slightly lower for the 54% plant. The optimal capacity factor depends upon the
In Fig. 2, the capacity factor of new pulverized coal plant is now varied to produce a range of electricity wholesale prices which meet the desired IRR of 14%. This is compared to the 68% CF CLFR/cavern storage solar plant which is also held to an IRR of 14%. The graph shows that the coal fired plant is more costly up to about a CF of 82%, and even at a CF of 90% is only $5 per MWhe less expensive than the 68% CF solar plant. This suggests that minimal measures such as low priced carbon trading
Wholesale Price of Electricity for 14% IRR 
Coal Plant Capacity Factor Fig. 2. Cost of electricity in the second project year required to produce a 14% IRR in high CF Coal and Solar scenarios. The Coal CF is allowed to vary while the CLFR storage plant is held at a 68% CF, close to the higher range of solar CFs possible using daily storage in midlatitudes such as NSW and California. 
would be sufficient to provide solar competitiveness against the cheapest baselaod coal fired plant.