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Estate of terraced houses Stenbråtlia near Oslo: 34 terraced houses built to the passive house standard have been equipped with roof-integrated plastic solar collectors.
© Harald Kicker, JKU Linz, Austria
Plastic solar collectors

The plastic collector is available in several popular lengths and can be adapted to any length of roof or facade.
© Aventa

Some of the houses in the residential area have a continuous roof terrace. The collectors are attached permanently to the roof terraces and laterally adjusted wind and privacy barriers and therefore fit in architecturally.
© Harald Kicker, JKU Linz, Austria

Low-cost collector integration in buildings

To promote the spread of solar thermal energy further, the cost of system components must come down. Under the stewardship of the Fraunhofer Institute for Solar Energy Systems ISE, scientists have developed collectors with absorbers and coverings produced from low-cost plastic. Over 30 terraced houses in the Mortensrud neighbourhood near Oslo in Norway have been fitted with the new technology and showcased recently to the public.

The solar energy plants in the Stenbråtlia residential area in Mortensrud cover 62 per cent of total consumption for hot water and heating of the passive houses. The collector surface area is 14 square metres per house. The gradient of the roofs was optimised for combined solar energy systems. The collectors are built into the roof and therefore benefit from additional thermal insulation. “An important aim of the research project was to develop collectors that could be optimally integrated into the building from an architectural perspective and which are simple and cost-effective to install,” explains Dr. Michael Köhl, project manager responsible at Fraunhofer ISE. “The collectors are designed such that they can be fitted by the same company that installs the roofing and facade elements.” The households are supplied with thermal energy via the heat transfer medium water in an unpressurised solar circuit. No additional heating installer is required to connect the collectors on the roof. This saves money during installation. Further savings are made in terms of the material: Plastic is used to replace conventional metals copper or aluminium on the absorber, and on the collector covering, plastic is again used in place of glass.

Plastic damaged by excessive temperature

The unpressurised solar circuit operates according to the “drain-back” method. If the temperature in the solar circuit exceeds a defined maximum limit, the heat transfer medium water flows into the drain-back tank from the collector, supply and return lines. The tank is fitted in the terraced houses of the residential area in Norway at the same height as the unpressurised buffer storage tank, which is exposed to atmospheric pressure. The solar circuit is discharged in particular on hot days and during extended periods of fine weather. When the solar circuit is running, the drain-back tank is virtually empty. The method eliminates stagnation problems caused by steam development and pressure in the collector remains low. This protects the plastic components as they are not exposed simultaneously to pressure and high temperatures. This is a distinct advantage as plastic is less temperature resistant than the materials used in a standard collector.

Two tanks produce one storage system

All 34 terraced houses are equipped with a buffer storage tank, which is located in a boiler room on the ground floor or in a well-insulated annex. “In the residential area in Mortensrud, we have used a tank-in-tank solution. The internal 100-litre tank is used for preheating domestic water, the external tank holds 800 litres and is used to store hot water to support the heating,” explains Dr. Michaela Meir, development department associate at Aventa. Solar and underfloor heating circuits are connected directly to the storage tank hydraulically without a heat exchanger. If the solar energy plant is no longer able to cover heat demand, an electric heating element provides further heating. The necessary power is supplied in Norway by hydroelectric power stations, which provide around 98 per cent of the country’s electrical power.

Research in European framework

The research project was implemented as part of the European joint project “Solar Collectors Made of Polymers”, SCOOP for short. Experts from the solar thermal and polymer industries are developing cost-effective and marketable solutions in this regard. The collectors used in Mortensrud are produced from plastic and manufactured by Norwegian industry partner Aventa.



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Project management
Fraunhofer ISE

Industrial partner


 SCOOP project website
Further information on the SCOOP project

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