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Alpine test rig: At Schneefernerhaus Environmental Research Station, the test collectors are mounted in front of the left side of the building.
© Fraunhofer ISE
Research projects revisited
18.01.2016

The close-up view shows the outdoor exposure test rig at Schneefernerhaus on the Zugspitze.
© Fraunhofer ISE

Maritime test rig near the sea: The image shows the collector test array near Pozo Izquierdo on Gran Canaria.
© Fraunhofer ISE

SpeedColl: Allowing collectors to age more quickly

Whether in maritime, arid or alpine regions, solar collectors must perform flawlessly for years. But to what extent do high UV radiation, salty and humid air take their toll on the collectors? In order to find out, researchers at Fraunhofer ISE and Stuttgart University exposed solar collectors to the wind and weather at six locations. The result: The collectors and the components are more durable than previously thought. However, that makes it even more difficult to make comparisons.

In the SpeedColl research project, researchers are developing accelerated ageing test methods for solar thermal collectors. To this end, they initially investigated various flat-plate collectors and components such as the glass, absorbers and reflectors. Scientists at the Fraunhofer Institute for Solar Energy Systems ISE and the Research and Testing Centre for Thermal Solar Systems (TZS), which belongs to the Institute for Thermodynamics and Thermal Engineering (ITW) at Stuttgart University, exposed the samples to wind and weather over a period of three years at six different locations around the world. The generated heat was not fed off during the entire test period. “Compared with normal operation, this creates a much greater burden on all components, so that the three years of outdoor exposure is equivalent to a significantly longer period in normal operation,” explains Dr Karl-Anders Weiß, head of the project at Fraunhofer ISE.

All climate zones relevant for using solar thermal systems were represented, ranging from the temperate climate in Stuttgart and Freiburg, and the tropical climate in Kochi in southern India with a high moisture load, to the Negev Desert in Israel and the Canary Islands with high sand, salt and UV exposure as well as the Zugspitze mountain with both extremely high and low temperatures, pronounced temperature changes and heavy snow loads. Parallel to this, the flat-plate collectors and their components were also tested in the laboratory by means of accelerated weathering tests.

“Both with the outdoor exposure at different climatic locations, as well as with the tests performed in laboratory stress tests, we haven’t been able to determine any significant performance degradation in regards to the investigated solar collectors,” concludes Weiß in summarising the test results. However, the latest results from collectors retrieved from the exposure test show signs of degradation on individual specimens, for example corrosion effects on mounting materials and absorbers following exposure on Gran Canaria, which can be explained by the different means of construction of the collectors, or the effects caused by large temperature fluctuations on the Zugspitze. The project manager adds: “We can also determine distinct changes in the respective characteristic values. However, since these are only isolated measurement values, we are not yet able to derive any models from them or validate the accelerated tests.”

Marginal difference compared with the condition when new

The only downside to this actually very positive outcome is that, because of the high quality of the products and the resulting minor changes compared to their condition when new, this meant that the main project goal was not fully achieved, namely the validation of testing methods for accelerated ageing. “After more than three years of outdoor exposure, we are still lacking the necessary reference values because the solar collectors are simply too good,” explains the project manager. He points out that these accelerated ageing testing methods are important, however, in order to be able to determine the service or operating life of the solar collectors for different locations and applications, thereby enabling, for example, the qualification of new developments that, using new materials or production processes, lead to cost reductions.

Further development of the ageing tests

The SpeedColl project finished at the end of December 2015. In a follow-up project, the scientists want to supplement the work begun and gain further information on the ageing behaviour of solar collectors. “We urgently need to provide validated ageing testing methods for industry in order to assess the service life with different conditions using models. We have already submitted a corresponding project proposal for ‘SpeedColl 2’ to Project Management Jülich,” says Weiß.

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Project management
Fraunhofer ISE

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SpeedColl
Further details about the project