Collectors last a long time

11.11.2015
Collectors and components installed at the Kochi test facility had to hold up under hot and humid weather conditions. (Photo: SpeedColl)
Collectors and components installed at the Kochi test facility had to hold up under hot and humid weather conditions. (Photo: SpeedColl)

What happens to a collector when it is exposed to the elements day in and day out? Does it lose a significant amount of its performance over the years or might the frame even crumble at some point? Researchers did not find evidence for any of this. Modern, industrially manufactured collectors are resilient. And not just in the moderate climate of central Europe, but also under extreme conditions such as in tropical India.

A consortium of researchers and industry specialists has now systematically and comprehensively studied the aging process of flat plate collectors and their components, including insulation, glass, absorber coating and adhesives. The SpeedColl project partners include the German research institutes ITW of the University of Stuttgart and the Freiburg Fraunhofer ISE as well as collector manufacturers and component suppliers.

Collectors were tested in the mountains, on the coast and in the desert

Collectors and their components were exposed to the elements at several locations around the world for three years. Even the most minor changes were meticulously documented. The hot, humid conditions in the Indian city of Kochi and the dry, dusty Negev Desert in Israel were particularly tough. In the coastal climate of Gran Canaria, the test installations had to withstand wind and salt spray.

Exposure to UV radiation was particularly high for systems installed on the Zugspitze. At a height of 3000 metres above sea level, it is Germany's highest mountain. The Zugspitze was also where the lowest as well as the highest absorber temperatures were recorded. Researchers were surprised by the fact that the temperatures were higher there than in more southern regions. According to Stephan Fischer from ITW, the main reason for this was the light reflected by snow.

Cleaning the collectors often helps to improve their performance

Collectors that were exposed to wind and weather on Gran Canaria showed the most visible signs of wear. After being exposed to the weather, the conversion factor was 3.4 to 4.3 percent below original values. However, when the glass was cleaned, the conversion factor was significantly improved and almost matched the original values.

At the locations Negev and Kochi, on the other hand, the reasons for the decrease in the conversion factor could not be washed off so easily. Sand had gotten inside of the collectors at the desert site, and in India, an opaque film had formed on the inside surface of the glass. Nevertheless, when the glass was cleaned, the conversion factor was only between 0.2 and 5.3 percent lower than that of a new collector. Collectors installed in southern Germany did not require cleaning, and conversion factors were not reduced at all.

This means that the main problem at locations with extreme weather conditions is actually dirt, not the degradation of the absorber coating or the glass pane. For this reason, Robert von Beulwitz from DSM Advanced Surfaces sees significant potential in the development of dirt-repellent coatings for solar glass.

Test methods for collectors

Previously, it was not known how hot the two-part silicone adhesive that holds the frame and glass together could get during stagnation. The researchers were able to determine that the temperature never exceeds 85 °C. Using this information, they developed two test methods. Part A determines the aging of the adhesive at 85 °C and 10% humidity. Part B tests at 40 °C and 95% humidity. The SpeedColl project also demonstrated that it is never hot as well as damp inside of the collector at the same time.

The consortium is also developing further tests for collectors, such as salt spray and UV testing. At some point in the future, these accelerated aging tests will be used to determine the service life of collectors. Will they last 20, 30 or even 40 years?

The tests cannot answer that question yet because the changes caused by natural weathering on the test installations were minimal up till now. Measurable changes have to occur in order to be able to compare aging simulations with reality. For this reason, the SpeedColl project will be extended so that more data can be gathered on collectors that are exposed to wind and weather. In addition, the researchers intend to study the effects of harmful gases in the atmosphere on the collectors.

For more information, please visit www.speedcoll.de/en/home.html

Jens Peter Meyer

 

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