Solar Thermal Collectors and their Components. Results of Long-term Exposure at Extreme Test Site
Abstract
The reliability of solar thermal collectors is of great economic importance for suppliers, manufacturers and operators due to the long lifetimes demanded by the market. However, it is naturally strongly influenced by the specific climatic conditions at the installation site and is therefore difficult for the industry to estimate. The determination of the load factors for collectors and components under the conditions of the various extreme outdoor weathering locations offers the possibility of influencing the design of thermal solar collectors and components. To quantify the ageing behavior of solar thermal collectors and their components, we exposed solar thermal flat plate collectors to locations in moderate as reference and with harsh conditions in tropical, alpine, arid and maritime climates. The performance of the solar thermal collectors was measured before and after the outdoor exposure. In order to quantify the influence of the soiling of the transparent cover, the collectors were measured without cleaning and after cleaning. After the performance test, the collectors were opened and subjected to a visual inspection. The effect of direct deposits on the absorber plate and the transparent cover were quantified using spectroscopic measurements. In this paper we present the results of the latest collector measurements. An exposure time of ten years under stagnation conditions was achieved. This exposure time corresponds to approx. 50 - 100 years of real operation, depending on the location and the application.