New technical solutions
for energy efficient
buildings
State of the Art Report
Photovoltaic/Thermal Systems
(PV/T)
Authors:
Martin Treberspurg, Mariam Djalili, BOKU
Heimo Staller, IFZ
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Background
Energy consumption is increasing drastically due to new areas of application and a variety of uses. Increased energy efficiency and the use of renewable energies are important measures to tackle these challenges. The EU 2020 targets were set to promote a focus on a sustainable future. Until 2020 cutting emissions of green house gases by 20%, reducing energy consumption by 20% through energy efficiency, and meeting 20% of our energy needs from renewable sources has to be achieved. Sun facing façades and roof areas of low energy buildings becomes a valuable area for the use of to renewable energies.
Photovoltaic/Thermal Systems
A photovoltaic/thermal hybrid solar collector (short: PV/T collector) is a combination of photovoltaic (PV) and solar thermal (T) components/systems which produce both electricity and heat from one integrated component. PV systems turn on average less than 20% of the sunlight into electricity. The remainder is turned into heat. Utilising this untapped energy is the general concept for hybrid systems. Through the application of systems that can provide both (thermal and electrical), the energy yield per area unit of roof or façade can be substantially increased. Further advantages are using heat transfer from PV-module, improvement of conversion efficiency of solar cells, increase of electric output1 and an aesthetically
appealing more uniform look.
A significant amount of research and development work on the PV/T technology has been done for the last four decades. Many innovative systems and products have been put forward and their quality eva-luated by academics and professionals. After a first systematic research in the early 1980s several PVT designs were made and tested. Due to a change of government funding research was discontinued and regained attention in the mid 1990s. Research and development activities on PV/T are spread worldwide and conducted in relatively small programmes. As a result the PVT development had to restrict itself to the application of market-ready PV technologies.2 In 2005 the international energy agency (IEA) started Task
35 “PV/Thermal Solar System” which focuses on development and market introduction of high quality and commercially competitive PV/Thermal Solar Systems.3 In this project a comprehensive overview on
commercially available PV/T products with technical and economical information and of building projects
1 The relative increase in solar cells efficiency as the result of cooling is in order of 10-30% (source: Ewa Radziemska
“Performance Analysis of a Photovoltaic-Thermal Integrated System”, Chemical Faculty, Gdansk University of Technology, 80-233 Gdansk, Poland, (2008)
2 Helden, W.G.J. van, Zolingen, R.J.C.van and Zondag, H.A. (2004) PV Thermal Systems: PV Panels Supplying Renewable
Electricity and Heat, Progress in Photovoltaics Vol 12, pp. 415–426.
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where PV/T systems have been integrated, has been worked out (see table 1 and 2, information available under: http://www.pv-t.org/).
Tab. 1 Overview of benefits of different PV/T design options [11]
Tab. 2 Market segments of PV/T: Future markets: +++, niche markets: ++ and + [11]
The hybrid system generates electricity that has a much higher quantity than produced heat. Therefore it is very difficult to compare the PV/T system with the customary thermal system. However, it is impossible to obtain the maximum electric and thermal efficiency simultaneously. Collaborations have been underway amongst institutions or countries, helping to identify suitable products and systems with the best marketing potential. To reach commercial breakthrough some challenges still need to be overcome. Product quality and ease of delivery, product standardization, warranties and performance certification, installation training and experience are important.
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PVT systems are considered to have a high potential and expected to become competitive with conven-tional power generation. Research in thermal absorber design and fabrication, material and coating selec-tion, energy conversion and effectiveness, performance testing, system optimisaselec-tion, control and reliability is important.4 Despite worldwide activities the number of commercially available collectors and systems is
still very limited. Individual set up depending on geographical location and actual application is necessary. Payback time depends on funding schemes for PV and Solar Thermal making the PV/T sector doubly sensitive to political decisions.
Calculations made by ECN (Energy research Centre of the Netherlands) within the above mentioned IEA-project showed that by using PV/T collectors instead of side by side systems it is possible to reduce the collector area by 40% with the same energy output.
PV/T Air Collectors
Air cooled PV panels for electrical and thermal gain is most suitable for building integrated PV systems and façade application (second skin).
SolarVenti – Solar Air & Solar Hybrid Collectors
SolarVenti introduced this patent to the market in 2001. The PVT collector was designed for automatic ventilation of summer cottages with PV on part of the absorber. Further uses are family houses, work-shops, garages, cellars, storerooms, boats, caravans and museums.
http://www.solarventi.com/index.htm
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Fig. 1 LEFT: SolarVenti PV/T Collector RIGHT: basic concept of SolarVenti module [1]
Grammer Solar – PV-Hybridcollector
Grammer Solar offers two products: Twinsolar, a PV/T-collector for ventilation of summer cottages with PV on part of the absorber and PV/T Hybridcollector, with PV over the whole absorber as shown in the figures below.
http://www.grammer-solar.de/unternehmen/index.shtml
Fig. 2 basic concept of the PV/T-module “Grammer Solar” [2]
Sun radiation
Insulation PV-cells
Air intake and outlet
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Fig. 3 reference projects using “Grammar Solar” modules [3]SolarWall PVT
The SolarWall PV/T system is a building integrated solution. PV modules are mounted on top of the SolarWall Panels. The heat is drawn off the back of the modules and is ducted into the buildings via conventional HVAC system where it offsets the heating load.
http://solarwall.com
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Technical Data:
Technology Watt/m²
PV Electrical Output 100 W/m²
SolarWall Thermal Output 200-300 W/m²5
Hybrid SolarWall PV/T 300-400 W/m²
Note: SolarWall output without PV is 500-600 W/m²
PV/T Liquid Collectors
Three companies are listed below that have developed liquid PV/T collectors.
PVTWINS – PVTWIN collector
PVTWINS is a spin-off company from the Energy research Centre of the Netherlands (ECN) founded in October 2004. They focus on PV/T products and customised PV/T-modules and distribute these products internationally with related system components like inverters and hot water storage vessels. Also, PVTWINS develops PVT products for niche markets, such as autonomous PVT water treatment units and PVT swimming pool collectors. http://pvtwins.nl
Fig. 5 PVTWIN collector [5]
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Technical Data:
PVT-collector Dimensions Collectorbox *(m)
Aperture (m2) Nom. Electrical output **(W) Nom. Thermal output **(W) PVTWIN 212 1.050 * 1.895 1.28 150 765 PVTWIN 313 1.050 * 2.760 1.92 220 1150 PVTWIN 422 1.895 * 1.895 2.56 295 1535 PVTWIN 515 1.050 * 4.245 3.20 370 1920 PVTWIN 616 1.050 * 5.325 3.84 440 2300 PVTWIN 623 1.895 * 2.760 3.84 440 2300 PVTWIN 824 1.895 * 3.615 5.12 590 590 PVTWIN 1025 1.895 * 4.245 6.40 735 3840
* The outer edge is 8 cm wide and covered with roof tiles when the collector is integrated in the roof.
** Component power at STC (irradiance 1000 W/m2 and ambient temperature 25°C). Depends on the type of solar cells.
Millenium Electric –- MSS Multi solar panel
Millenium Electric offers MSS multisolarpanel with the added function of hot water and air heating.
http://www.millenniumsolar.com/
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Technical Data:
Product Thermal Electrical
MSS-MIL-PVT-190W-M02 (1580 x 808 x 45 mm)
2000 Kcal/Day 190 W
MSS-MIL-PVT-195W-M03 Black on Black (1580 x 808 x 40 mm)
2000 Kcal/Day 195 W
RES Energy Kombimodul
„RES Energy Kombimodul” offer PV-modules with an integrated copper heat exchanger for cooling the PV cells and generating thermal energy.
• An integrated hydraulic circuit cools the heat-sensitive photovoltaic cells generating up to 20%
higher power output.
• Thermal energy is used for heating or stored in seasonal ground storage.
• The hydraulic circuit uses the evaporative cooling (dew in the morning) and at night to
gene-rate cooling energy for passive cooling.
• In winter modules are briefly heated to free them of snow before energy generation is continued. • Roof integrated modules are frameless and offer a visually appealing, uniform collector surface.
http://www.solardoc.at/
http://www.res-energie.eu/index.html
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Fig. 7 LEFT & RIGHT: project references [7]Technical Data:
Product (size in mm:1633 x 991 x 40) Thermal6 Electrical
res-PV++ 220 865 W 220 Wp
res-PV++ 230 865 W 230 Wp
res-PV++ 240 865 W 240 Wp
PV/T Concentrators
Two companies offering PV/T concentrators are listed below.
Arontis solar solutions – Solar 8
Solar 8 is a one-axis tracking, modular PV/T concentrating collector for building as well as ground installations. Application for hotel roof tops, hospitals, sports, recreation, airports, restaurants, supermarkets etc.
http://www.absolicon.com/
Fig. 8 LEFT: prototype testing; RIGHT: demonstration installation in Sweden [8]
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Fig. 9 Technical Data [9]Menova Engineering Inc – Power Spar
The Power-Spar® mounting systems are suitable for commercial flat roofs (non-penetrating), ground mounted units or raised parking lot structures.
• Utility Scale Projects: Applications in solar fields for augmenting existing power generation sites • Building Integrated Projects: Commercial/business applications
• Infrastructure Projects: Water treatment, sewage treatment & desalination plants
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Fig. 10 Menova Power Spar concentrator for parking lot structures [10]Technical Data:
Product Thermal Electrical
PS-140 Solar Concentrator
Size: 8810 mm h x 17900mm swing diameter
28 kWe AC 42 kWth
PS-35 Solar Concentrator
Size: 8515 mm h x 8900 mm swing diameter
7 kWe AC 10 kWth
Recommendations for procurers
• If solar energy use is planned, solar collector areas need to be considered in early design
stages, as they will have huge impact on the building design. This has to be taken into account by procurers especially for architectural design competitions.
• By the use of PV/T collectors the collector area can be reduced up to 40% providing the same
energy output as conventional side by side systems. So alternative tendering for PV/T collectors should be considered when electrical (PV) and thermal solar energy use is planned.
• Assessment of different bids must be done on thermal and electrical output. But the economical
savings of PV/T systems by reduced substructure areas (façade, roof) should also be taken into account.
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• Comparisons/assessment of the environmental impact of PV/T solar systems should be done on
the primary energy level and on CO2- emissions. If possible, technical specifications in tendering
documents should deal with benchmark values of primary energy and CO2- emissions. It is
recommended to use primary energy savings as a measure for the value of energy saving and using it during design and in the tendering process for comparison/assessment of different bids.
• For PV/T systems there are no internationally accepted standards on performance, testing,
monitoring and on commercial characteristics, additional expertise (e. g. for the definition of technical and environmental specifications, assessment of bids) for the whole procurement process is required.
• As the calculation of costs (such as payback times) in comparison to conventional systems is
quite complex, expert input is required. Generally speaking costs (payback times) are effected by the following aspects:
o Solar radiation on the site o Efficiency of the HVAC system
o Construction costs for the HVAC system
o Additional construction costs for the implementation of the solar panels in the building structure
o Operation costs of the HVAC system
o Future development of interest on borrowings o Future development of energy prices
References
[1] http://www.solarventi.com/index.htm [2] http://www.grammer-solar.de [3] http://www.grammer-solar.de [4] http://solarwall.com [5] http://pvtwins.nl [6] http://www.millenniumsolar.com/ [7] http://www.res-energie.eu/index.html[8] LEFT: http://www.arontis.se, RIGHT: http://www.absolicon.com/_about_solar_energy/1070_press_eng.php [9] http://www.absolicon.com/_solar_collector/1026_x10_data_eng.php
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[11] Hansen, Sörensen, Byström, Collins, Karisson, "Market , modelling, testing and demonstration in the framework of IEA task 35 on PV/ thermal solar systems", paper 22nd European Photovoltaic Solar Energy Conference and Exhibition, 3-7 September
