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Scientists at Fraunhofer ISE are investigating the ageing of solar collectors and their components under extreme climatic conditions in the Negev Desert in Israel.
© Fraunhofer ISE
Test rigs for solar collectors
12.05.2014

The image shows exposed metal coupons for determining the corrosiveness of the atmosphere at the maritime test facility on the Spanish island of Gran Canaria.
© Fraunhofer ISE

Accelerated ageing of collectors

In the desert, in the Alps and along the coast: at these locations, solar collectors are exposed to a combination of high UV radiation along with salty and humid air. That stresses the components in solar thermal systems and makes them age faster. Until now, however, this has not been adequately investigated. For this reason, Fraunhofer ISE is now developing tests to accelerate the ageing of collectors in different climate conditions. The preliminary findings are being provided by the SpeedColl project.

Collectors are the most heavily stressed components in solar thermal systems. Depending on the location, they are exposed to high temperatures and partly changing, partly extreme weather conditions. For example, sun-rich, densely populated coastal areas are highly suitable for using solar thermal systems. However, in addition to high UV radiation and humidity, collectors there are also exposed to salty air, which degrades them. Until now, the ageing of solar collectors and their components in different applications and conditions has hardly been investigated. Rapid test procedures are therefore required to determine the ageing resistance of the collectors. The results can help increase export opportunities and minimise risks for potential buyers. In the “SpeedColl” project, researchers from the Fraunhofer Institute for Solar Energy Systems ISE, Stuttgart University’s Institute of Thermodynamics and Thermal Engineering (ITW) and 20 companies are therefore developing accelerated ageing tests for solar collectors and their components.

In order to simulate a long service life, increased UV radiation relative to normal daylight and environmental chambers with salt spray tests can be used for example. The accelerated tests should make it possible to predict how long specific collectors can be operated under what conditions and with what outputs.

The location determines the collector ageing

“How quickly components age precisely depends on the location and the conditions. In salty air, metallic components such as absorbers, mirrors and frames corrode more,” says Karl Anders Weiß, Group Manager for Service Life Analysis at Fraunhofer ISE. In hot and dry climates, on the other hand, the UV exposure is greater, which has a greater adverse effect on polymer components, adds Weiß.
Initial follow-up measurements in Gran Canaria have shown that the collectors are technically quite reliable. Despite the challenging conditions, no reduction in the output has been determined for the collectors exposed there. It was also shown that the actual stresses on the materials and components used depend considerably on the structural design of the collectors and the installation location. “Using the measured meteorological and material-specific data, we are developing test procedures to test the suitability of solar collectors for sun-rich areas,” explains Karl Anders Weiß.

Rapid test procedures not only provide valuable information for developing new kinds of collectors, their quality guarantee also provides a decisive competitive bonus for German industry. Until now, solar collectors have been considered to have a guaranteed service life of at least 20 years. This value has resulted from the experience gained from the Solarthermie2000 and Solarthermie2000plus funding programmes. The accelerated test methods now being developed will be compared and evaluated with, for example, measurement values taken over several years from test rigs. These test rigs are located on the Zugspitze, in Freiburg, Stuttgart, Gran Canaria, India and the Negev Desert in Israel. In addition, the solar collectors and components will also undergo accelerated weathering tests in the laboratory, as is being carried out in the MechTest project (BINE Information Service reported). There, mechanical loads are being tested on the collectors under real conditions.

Improving the service life in future

If the test results from SpeedColl are taken into account in future when designing collectors and selecting materials, this would enable their durability to be improved even further. “We even expect that this will enable costs to be saved,” forecasts Group Manager Karl Anders Weiß.
The project is being funded by the German Federal Ministry for Economic Affairs and Energy until spring 2015. Comprehensive test results are expected by then.

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