Труды Всемирного конгресса Международного общества солнечной энергии - 2007. Том 2
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Proceedings of ISES Solar World Congress 2007: Solar Energy and Human Settlement
792
On the other hand, the thermal losses during the night are
calculated from the equation:
mc T T
U
TT
()−
=
−
(4)
Table 1 summarises the results obtained in the early five
days of tests.
TABLE 1: PERFORMANCE OF THE TWO-PHASE AND
THE CONVENTIONAL SYSTEMS
RESULTS
WATER
SYSTEM
R134a ACETONE
η 50.6±3.1 51.5±2.6 40.1±1.6
q [MJ] 14±1 14.5±1.3 12.9±1.8
T [K] 50.3±2.6 50.3±2.1 48.1±3.2
TΔ [K] 21.3±1.4 21.7±1.9 19.7±2.8
T [K] 45.9±3.5 46.6±2.3 46±0
U [MJ/K] 0.445±0.035 0.44±0.06 0.44±0.00
NOTE: Rounding of mean values was done according to standard deviation
data.
Figure 4 shows the efficiencies of the two-phase
thermosyphon working with R134a and the conventional
thermosyphon. Although the two-phase system exhibits a
slightly better performance, a simple analysis indicates that
the efficiencies are statistically equivalent; see Table 1.
Fig. 4: Efficiencies of the two-phase thermosyphon
working with R134a and the conventional
thermosyphon.
It can be seen from table 1 that acetone has a lower
performance, however more tests must be carried out to
obtain a solid conclusion to this question; according to Soin
et al. [2] the system must be loaded with a larger quantity
of the working fluid to obtain a better performance.
After the irradiation period (at around 18:00 h), the
temperature in the thermotank has increased around 21 °C
to reach a temperature of 50.3 °C for both the conventional
system and the two-phase working with R134a. Once again,
the temperature increments for the two-phase system
working with acetone is lower, and reaches an average
temperature of 48.1 °C, though its mean value is lower than
the former two, the temperature is statistically equivalent
due to its high standard deviation.
After including the thermal losses during the night, we
obtain the available temperature after the next morning of
one day of test, which goes around 46 °C. That is to say,
thermal losses reduce around 4 of 5 °C the temperature of
the water in the thermotanks. For the case of acetone, only
one data of thermal losses could be collected to conclude
about its performance.
4. CONCLUSIONS
A two-phase closed thermosyphon using R134a and
acetone as working fluids was compared with a
conventional natural solar collector thermosyphon. In the
early days of tests, the two-phase system working with
R134a showed statistically equivalent performance than the
conventional system, though the former eliminates
problems of freezing, fouling, scaling and corrosion. The
two-phase system working with acetone showed a slightly
lower performance; however, it is expected to improve after
new tests with major loads of acetone in the closed circuit
of the system.
5. NOMENCLATURE
A
: Absorber Area, m
2
c : Specific heat at constant pressure, J/kgK
I
: Irradiance on the collector plane, W/m
2
m: Mass, kg
n: The night period
3 SOLAR COLLECTOR TECHNOLOGIES AND SYSTEMS
793
q : Energy received from the Sun, J
q : Useful heat, J
T : Available temperature at the end of the solar
irradiance period, [K]
T : Available temperature after one day of test, [K]
TΔ : Temperature increment, K
tΔ : Time of operation of the system, s
U : Thermal losses during the night, [J/K]
η : Efficiency
6. ACKNOWLEDGMENTS
This work has been partially financed by CONACyT project
U44764-Y and Modulo Solar S.A. de C.V. company.
The authors thank to CONACyT for the support provided
to the student with the scholarship number 183846.
7. REFERENCES
(1) S. A. Kalogirou, “Environmental benefits of domestic
solar water heating systems”, Energy Conversion &
Management 45 (18-19) (2004) 3075-3092.
(2) R. Soin, K. Sangameswar Rao, D. Rao, K. Rao, Performance
of a flat plate solar collector with fluid undergoing phase
change, Solar Energy 23 (1) (1979) 69-73.
(3) J. M. Schreyer, “Residential application of refrigerant-
charged solar collectors”, Solar Energy 26 (4) (1981)
307-312.
(4) J. M. Calm, D. A. Didion, “Trade-offs in refrigerant
selections: past, present and future”, International
Journal of Refrigeration 21 (4) (1998) 308-321.
(5) K. S. Ong, M. Haider-E-Alahi, “Performance of a
R-134a-filled thermosyphon”, Applied Thermal
Engineering 23 (18) (2003) 2373-2381.
(6) H. M. S. Hussein, “Transient investigation of a two
phase-closed thermosyphon flat plate solar water
heater”, Energy Conversion & Management 43 (18)
(2002) 2479-2492.
(7) H. M. S. Hussein, “Optimization of a natural
circulation two phase closed thermosyphon flat plate
solar water heater”, Energy Conversion & Management
44 (14) (2003) 2341-2352.
(8) M. Esen, H. Esen, “Experimental investigation of a
two-phase closed thermosyphon solar water heater”,
Solar Energy 79 (5) (2005) 459-468.
(9) Refprop version 7.0. Reference Fluid Thermodynamic
and Transport Properties, NIST Standard Reference
Database 23, Lemon E.W., McLinden M.O., Huber
M.L., USA (2002).
(10) N. v. Solms, M. L. Michelsen, G. M. Kontogeorgis,
“Applying association theories to polar fluids”, Ind.
Eng. Chem. Res., 43 (2004) 1803-1806.
EXPERIMENTAL STUDY ON OPTIMAL HEATING METHODS OF WALL-MOUNTED
SOLAR AIR COLLECTOR
B. Chen, H. Tian
Laboratory of Building Environment and New Energy Resources, Dalian University of Technology,
Dalian, Liaoning 116024, China
chenbin8911@yahoo.com.cn
ABSTRACT
Passive solar houses based on Trombe wall principle have
been extensively used in rural homes in northern China.
Some novel solar air collectors have been developed in
order to suit for existing building reconstruction and urban
buildings. But the most researches of this field mainly
focus on the thermal efficiency of solar collectors and
Trombe-Wall. The fact that heating room temperature is
low while the thermal efficiency of collectors is high has
been the general problem. In this paper, the heating method
with Wall-mounted Solar Air Collector (WSAC) is studied.
The influence factors and actual effect with these advanced
strategy were experimentally analyzed. The results are
beneficial to design of solar air collector integrated
building.
1. INTRODUCTION
Passive solar house, which has improved indoor thermal
environment condition of rural houses and saved lots of
coal consumed for heating in winter, is popularized in cold
rural areas in China (eg. Liangning, Gansu) for twenty
years. However, a few main problem of the traditional
Trombe-Wall are hard to maintain and poor construction
quality. For renovation of building stocks and application
of solar heating technique for future urban buildings,
wall-mounted solar air collector (WSAC) is developed.
Solar air collector basing on solar chimney principle has
extensively been studied, and most of them focus on
collectors performances through experimental research and
theoretical analysis. Some studies tried to enhance thermal
efficiency of collectors by analyzing the factors affecting
thermal performance, improving the configuration of
collectors. However, the results of field survey have shown
that indoor air temperature is lower than wanted condition
even though the air supply temperature of collectors is very
high. It means that actual heating effect depend not only on
thermal efficiency of collectors but also building types,
process of heat transport and space air diffusion.
The passive heating technology is popularly mainly
adopted in rural areas of China until now, so there is few
research on solar air collector have been found. In this
study, WSAC has been developed, the Factors of affecting
heating effect is experimentally analyzed, and some
strategies for improving heating effect have been presented.
2. EXPERIMENT
2.1 Experimental Set-up
The test room with size of 3.9h3.9h2.7 m
3
and solar air
collectors located wall between window and under window
are shown in Fig. 1. The exterior walls are consisted of
300mm cinder concrete hollow block, and ceiling were
insulated by using 100mm thick styrofoam panels.
Tested WSAC-1 and WASC-2 are considered as the model
3 SOLAR COLLECTOR TECHNOLOGIES AND SYSTEMS
795
of WSAC on wall between windows and the model of
WSAC on window wall respectively. The dimensional size
of them were (widthh height) 1100mmh1870mm and
1980mmh860mm. The air gap of the collectors is 60mm,
and diameter of the inlets and outlets are all 120mm. The
air thermo-circulation principle is same as Trombe-Wall.
Fig. 1: Experimental set-up.
2.2 Experimental Method
The experiment has been performed during the winter of
2007, and the test points position are shown in Fig 2.
The temperatures of all test point were measured by digit
data logger with a time interval of 10min. The solar radiant
intensity was measured by the pyranometer. Air velocity is
measured by hot-wire anemometer.
(a)Wall between windows (b) Wall under window
Fig. 2: Schematic diagrams of the test points location.
3. TEMPERATURE DROP DURING TRANSPORT
PROCESS
The experimental results about temperature drop during
transport process are shown in Fig. 3. It can be found that
the highest temperature drop is up to about 50 ć just
through wall body, meanwhile air temperature distribution
in inside collector and space were shown in Fig.4. It can be
seen that ideal heating effect can not be achieved without
suitable design in transport process, even if the thermal
efficiency of collector is high.
-10
10
30
50
70
90
2-14 08:00
2-14 14:00
2-15 10:50
2-15 16:50
2-16 13:40
2-17 10:30
2-17 16:30
2-18 13:20
2-19 10:10
2-19 16:10
2-20 13:00
Tim e
Temperature/°C
Fig. 3: Temperature declining of outlet of collector.
Fig. 4: Temperature distribution during thermal circulation.
T
og-1
T
o-1
T
nu200-1
T
in
T
mu-1
T
su200-1
Proceedings of ISES Solar World Congress 2007: Solar Energy and Human Settlement
796
4. FACTORS ANALYSIS AFFECTING HEATING
EFFECT
From discussed above, it is found that the heating effect
was mostly influenced by the heat transport process and
space air diffusion. Air circulating process using MSAC
for heating can be divided into three sections, namely,
collector section, heat transport section and space air
diffusion section. So far, few researches have been done on
the later two sections. Experimental analysis on them has
been done in this study.
4.1 Heat Loss Through Wall body
Two cases, use 2cm rock wool for heat insulation around
the path through wall or not, were chosen to measure
temperature drop when the hot air from collectors pass
through the wall. The experiment data is shown in Fig. 5.
The results show that the thermal insulation can effectively
reduce heat loss, no matter for natural or forced convection.
And at the same mode, the temperature drop for forced
convection is less than one for natural convection. It can be
conclude that heat loss can be reduced at lest 50% if heat
insulation is implemented in path through wall.
4.2 Air Flow
4.2.1 Natural Convection
For natural convection, the drive of air circulation come
from the temperature difference of outlet and inlet of
collector. The air velocity is rather slow when on-way
resistance is higher. The mean air velocity of outlet of
collector is about 0.2m/s. As a result, hot air bulk from
solar air collector became cool rapidly due to heat
exchange with cold air close to exterior wall, then went
down along the exterior wall and enter into lower vent
without well heat exchange with indoor air. Therefore,
forced convection is necessary for improving the character
of hot air circulation.
4.2.2 Forced Convection
In this study, two ways of air flow under forced convection
is adopted: the one is done by solar fan, the other is fan
0
10
20
30
40
50
60
0 2040 6080100120
Tim e/m in
Temperature/°C
(a) Natural circulation
0
10
20
30
40
50
60
0 20406080100120
Tim e/m in
Temperature/°C
(b) Forced circulation
Fig. 5: Effect of thermal insulation in path through wall.
driven by electricity. In this paper, the result by solar fan is
not taken into account.
Take outlet temperature of collector and time of fan
operation as the controls parameter respectively. From Fig. 6,
can be found that the indoor temperature is nearly no
change under temperature control mode; oppositely
intermittent forced convection mode brings good effect on
heating with lower outlet air temperature of collector
compared with natural convection mode.
4.3 Space Air Diffusion
1m long duct was installed at the upper vent in indoor side
to improve heating effect. Additional, the heat insulation in
route of hot air supply (through-wall body) was made. Indoor
With Thermal
Insulation:
T
o-2
T
og-2
T
og-2
-T
o-2
Without Thermal
Insulation:
T
og-2
T
o-2
T
og-2
-T
o-2
3 SOLAR COLLECTOR TECHNOLOGIES AND SYSTEMS
797
0
20
40
60
80
10:10
10:30
10:50
11:10
11:30
11:50
12:10
12:30
12:50
13:10
13:30
Tim e
Temperature/°C
Fig. 6: Effect of air flow on indoor thermal environment.
temperature was measured on intermittent forced
circulation conditions, shown as Fig. 7. It is found that the
air temperature at the outlet of the extended duct( one meter
away from inner south wall) is obviously higher than the
one of the same position without extended duct. At the
same time, the air inlet temperature of the collector is
slightly lower than the one without extended duct. It
illustrate that the hot air can be transported effectively to
the inner room with the good air diffusion, and can prevent
“short-circuit”.
10
15
20
25
30
35
40
10:10
10:30
10:50
11:10
11:30
11:50
12:10
12:30
12:50
13:10
13:30
13:50
14:10
Tim e
Temperature/°C
Fig.7: Effect of space air diffusion.
5. CONCLUSIONS
(1) Heat insulation on wall-through duct is very necessary
for MSAC system; in this study, the simple heat insulation
increases more than 50% heat supply. It can be forecasted
that appropriate heat insulation will reduce heat loss
greatly.
(2) Intermittent forced circulation improves space heating
effect obviously. The optimal runtime of fan and air
velocity remain to be investigated in future.
(3) The effect of air diffusion is very important to
optimizing heating effect.
6. REFERENCES
(1) Z.D. Chen, P. Bandopadhayay, J. Halldorsson, C.
Byrjalsen, P. Heiselberg, Y. Li. “An Experimental
Investigation of A Solar Chimney Model with Uniform
Wall Heat Flux”. Building and Environment, 2003, 38
(7): 893-906.
(2) Arvind Tiwari, M.S. Sodha. “Parametric Study of
Various Configurations of Hybrid PV/thermal Air
Collector: Experimental Validation of Theoretical
Model”. Solar Energy Materials & Solar Cells, 2007,
91 (1): 17-28.
(3) Wenxian Lin, Wenfeng Gao, Tao Liu. “A Parametric
Study on The Thermal Performance of Cross-
corrugated Solar Air Collectors”. Applied Thermal
Engineering, 2006 ,26 (10): 1043-1053.
(4) X.Q. Zhai, Y.J. Dai, R.Z. Wang. “Experimental
Investigation On Air Heating and Natural Ventilation of
A Solar Air Collector”. Energy and Buildings, 2005, 37
(4): 373-381.
(5) Ben Slama Romdhane. “The Air Solar Collectors:
Comparative Study, Introduction of Baffles to Favor the
Heat Transfer”. Solar Energy, 2007, 81 (1): 139-149.
(6) Md Azharul KarimˈM.N.A. Hawlader. “Performance
Evaluation of A V-groove Solar Air Collector for
Drying Applications”. Applied Thermal Engineering,
2006, 26 (1): 121-130.
(7) Ucar, M. Inalh. “Thermal and Exergy Analysis of Solar
Air Collectors with Passive Augmentation Techniques”.
International Communications in Heat and Mass
Forced circulation:
T
og-1
Natural circulation:
T
1000-2
T
in
T
i-2
With
With
Witho
ut duct
Witho
Proceedings of ISES Solar World Congress 2007: Solar Energy and Human Settlement
798
Transfer, 2006, 33 (10): 1281-1290.
(8) Turhan Koyuncu. “Performance of Various Design of
Solar Air Heaters for Crop Drying Applications”.
Renewable Energy, 2006, 31 (7): 1073-1088.
(9) Chen Bin, Zhuang Zhi and Yang Wenxiu. “Indoor Thermal
Environment of Rural Residences in A Coupled Heating Pattern
of Passive Solar-collected Wall and Oven-kang Com-
bination”. NUANTONGKONGTIAO, 2007, 36(2): 20-24.
(10) Chen Bin, Xue Jing, Yang Wenxiu. “Experimental Study on
Thermal Performance of an Advanced Solar Air Collector
with Colored Facade in Winter”
. NUANTONGKONGTIAO,
2007, 37(8).
LARGE-SCALE SOLAR HEATING AND COOLING SYSTEMS IN EUROPE
Jan-Olof Dalenbäck
Chalmers University of Technology
Dept. of Energy and Environment
SE - 412 96 Göteborg, Sweden
jan-olof.dalenaback@chalmers.se
ABSTRACT
In total, there are about 19 million m
2
of glazed solar
collectors in Europe, corresponding to about 13,5 GW
th
,
where the majority of the collectors are installed in small
systems with up to a few kW
th
. However, the relevant
heat loads vary from a few kW
th
up to several GW
th
and
about 9% of the heating loads in Europe are covered by
block and district heating systems. So far, only a minor
part of the European collector market comprises large-scale
applications. European large-scale solar heating plants
having more than 500 m
2
(~350 kW
th
) of solar collectors
have only about 140 MW
th
altogether, i.e. about 1% of the
present installations in Europe. There is thus a need to
develop large-scale applications in order to utilize the full
potential of solar heat to cover existing heat loads.
The first large-scale solar heating applications were
introduced in Sweden in the late 70’s. Interests in
large-scale solar heating, especially in Germany and
Austria, increased during the 90’s and about 100 plants
with more than 500 m² of solar collectors are put into
operation since mid 90’s. Large-scale plants show more
favourable costs of solar heat than most small systems and
a strong market growth for small systems in Spain and
France could now lead to an increased interest for
large-scale applications also in Southern Europe.
However, Sweden is still the leading country with 22 out of
about 120 European large-scale plants (>500 m
2
; >350
kW
th
) in operation.
The majority of large-scale solar applications are installed
in block and district heating systems, but there are now also
an increasing number of solar cooling plants. The paper
gives an update on the present status and describes initial
visions and strategies to increase the development of
large-scale solar thermal applications within the European
Solar Thermal Technology Platform (ESTTP) in
co-operation with representatives for Euroheat & Power.
1. INTRODUCTION
There are about 19 million m²
of glazed solar collectors in
Europe with a total (nominal) power of 13,5 GW
th
. Solar
collectors are mainly installed in small systems (2 – 30 m²)
and so far only a minor part is related to large-scale
applications. At present, there are about 120 documented
plants having more than 500 m²
(~350 kW
th
) of solar
collectors. The total collector area of about 200 000 m²
(~140 MW
th
) in these plants corresponds to 1% of the total
installations or about 50 000 SDHW systems.
Large-scale solar heating systems were introduced in the
late 70’s by the interest to develop solar heating systems
with seasonal storage. Sweden had a leading role in the
early demonstrations together with The Netherlands and
Denmark. In the 90’s the interest in large-scale solar
heating increased in Germany and Austria and about 100
new plants with more than 500 m² of solar collectors have
been put into operation since the mid 90’s. At present
there are about 120 plants with more than 500 m
2
of solar
collectors in operation in Europe. Out of these 30 plants
have a nominal design power of 1 MW
th
or more.
Proceedings of ISES Solar World Congress 2007: Solar Energy and Human Settlement
800
The present developments include mainly large-scale plants
with diurnal storage for residential heating, but also industries
and heat driven cooling applications in Southern Europe. A
continued interest to develop plants with seasonal storage
remains mainly in Denmark and Germany [2].
The no of plants in different countries is shown in TABLE
1. Sweden is still the leading country with a total of 22
plants in operation, although eight plants, the first from
1979, have been closed after 10-20 years of operation and
evaluation. The distribution of plants related to year of
commission is shown in Fig. 1. There was a negative
trend [1], but there seems to be an increased interest the last
two years with so far eight new plants in 2006 and 2007.
TABLE 1: LARGE SCALE PLANTS IN EUROPE
Country First Oper. Down
Sweden 1979 22 8
Germany 1993 18 1
Austria 1995 14 2
Greece 1986 14
Spain 1999 13
Denmark 1988 10
The Netherlands 1985 8
Switzerland 1995 7
Italy 2002 3
France 1999 3
Poland 2004 3
Others 2000 4 1
Total 119 12
European solar heating & cooling plants >500 m2
0
5
10
15
79 84 89 94 99 04
Closed (12)
Cooling (9)
Heating (110)
Fig. 1: Solar heating and cooling plants with >500 m
2
of
solar collector area built in Europe.
The oldest plant still in operation is from 1984 but the
majority of plants have been in operation for 10 years or
less.
2. APPLICATIONS AND TECHNOLOGIES
The majority of the large-scale plants supply heat to
residential buildings. The largest solar heating plants (>2
MW
th
) are listed in Table 2.
TABLE 2: SOLAR HEATING PLANTS IN EU
Plant,
Year in operation, Country
Coll.area
(m²)
Size
(MW
th
)
Marstal, 1996, DK 18 300 12,8
Kungälv, 2000, SE 10 000 7,0
Brædstrup, 2007, DK 8 000 5,6
Nykvarn, 1984, SE 7 500 5,2
Graz (AEVG), 2006, AT 5 600 3,9
Falkenberg, 1989, SE 5 500 3,8
Neckarsulm, 1997, DE 5 470 3,8
Crailsheim, 2003, DE 5 470 3,8
Ulsted, 2006, DK 5 000 3,5
Ærøskøping, 1998, DK 4 900 3,4
Friedrichshafen, 1996, DE 4 050 2,8
Rise, 2001, DK 3 575 2,5
Ry, 1988, DK 3 040 2,1
Hamburg, 1996, DE 3 000 2,1
Schalkwijk, 2002, NL 2 900 2,0
München, 2007, DE 2 900 2,0
Typical operating temperatures range from low 30°C to
high around 100°C (water storage). Two thirds of these
plants are connected to existing buildings, especially in
Sweden, Denmark and Austria. A large part of the plants
in Sweden and Austria are built in connection to wood fuel
fired heating plants. Non-residential plants are e.g.
installed in industries and commercial buildings.
The majority of the plants are designed to cover the
summer heat load - i.e. hot water and heat distribution
losses - using diurnal water storages, but 20 plants are
equipped with seasonal storages and cover a larger part of
the load. The seasonal storages comprise water in
3 SOLAR COLLECTOR TECHNOLOGIES AND SYSTEMS
801
insulated tanks (above or in ground) in 10 plants, the
ground itself in seven, aquifers in two and a combination of
ground and water in one plant. Nine plants are designed
to cover the summer cooling load in heat driven cooling
applications (Table 3).
Most of the plants have roof-integrated or roof-mounted
solar collectors while 18 plants in Sweden and Denmark
have ground-mounted collector arrays. More than 80% of
the plants are equipped with flat plate collectors, mostly
large-module collector designs. In a couple of cases in
Sweden and Germany roof-mounted collectors are designed
as more or less complete roof modules. Most plants have
pressurised collector systems with an anti-freeze mixture;
usually glycol and water, while four plants in the
Netherlands have drain back collector systems.
2.1 District Heating
The Swedish
large-scale solar heating plants are used by
district heating and housing companies, mainly for existing
building areas, using both ground mounted collector arrays
and roof-integrated or mounted collectors. The oldest
plant still in operation dates from 1984. Kungälv Energi
AB has recently built a 10 000 m² ground-mounted
collector array as a complement to an existing wood-chips
boiler plant (Fig. 2). The plant yields close to 4 GWh/a
out of a total load of about 100 GWh/a. Recent
developments comprise decentralised solar systems
connected to the primary district heating network in the city
of Malmö.
Fig. 2: Solar district heating plant in Kungälv, SE.
The Danish
large-scale solar heating plants are used in
small district heating systems and all collectors are ground
mounted.
Based on Swedish experiences the first Danish plant, with
1 000 m² of ground-mounted collectors, was built in Saltum
1987. In 1995 Marstal Fjernvarme A.m.b.a. decided to
establish about 8 000 m
2
solar collectors and a 2 100 m
3
water storage tank to cover up to 15% of their heating load.
The Marstal plant is now extended to 18 300 m
2
(12,8
MWth) and is so far the largest solar heating plant in
Europe (Fig. 3). A recent study of the future potential for
solar district heating in Denmark has resulted in two new
plants with 3,5 and 5,6 MWth.
Fig. 3: Solar district heating plant in Marstal, DK.
2.2 Block Heating
The Swedish housing company EKSTA Bostads AB
pioneered the use of roof-integrated solar collectors in new
building areas already in the 80's. At present EKSTA
owns and operates about 7 000 m² of roof-integrated
collectors. Initially EKSTA used site-built collectors, but
the latest development, a roof module collector mounted
directly on the roof trusses, has now been applied in a
couple of recent projects in new, as well as on, existing
buildings. This development has resulted in even better
integration in the building process, as well as further
reduced investment cost and improved thermal perfor-
mance.
The German
large-scale solar heating plants are mainly
applied in new residential building areas using
roof-integrated or mounted collectors. Some of the large
projects have so called “solar roofs”. Until 2003 eight
projects with seasonal storage, and about 50 large- to
medium-scale projects with short-term storage, had been
realised within the Solarthermie2000 programme. There
are e.g. two plants with >5 000 m² of roof-integrated