Accelerated Aging Tests of Absorber Coatings Used in Unglazed Metallic Collectors
Abstract
During the expected minimum life-span of 20 years, the absorber coating of unglazed thermal solar collectors is directly exposed to different stresses like heat, rain and ice. Thus, accelerated lifetime testing of absorber coatings should be performed to estimate their expected service life. However, there is no standard procedure available to assess the durability of metal absorbers for unglazed collectors. Existing tests (ISO 22975-3) are designed for absorbers used in glazed solar collectors, where the degradation loads (e.g. for humidity and condensation) are very different. With increasing application possibilities for unglazed metallic solar collectors (e.g. ground heat source regeneration), there is a need for the quality certification of absorber coatings. Durability assessment of spectrally selective absorber coatings for unglazed metallic solar thermal collectors is presented.