In the past decade, a testing procedure on accelerated lifetime testing (ALT) of absorber surfaces for solar thermal flat plate collectors has been established [7-9]. This qualification procedure is based on a general methodology for service lifetime assessment of solar energy materials worked out within the framework of Task 10 [10], Task 27 [11], and the Working Group MSTC [12] of the IEA Solar Heating and Cooling Programme. In the development of the procedure it was assumed that the intended use of the absorber surface to be qualified was in single-glazed flat plate collectors for domestic hot water (DHW) production. The absorber surface should be considered to be qualified if it meets the requirement of a design service life of 25 years with a maximum loss in the optical performance leading to a reduction in the overall DHW system performance of 5%.
Within this project a thickness insensitive solar selective (TISS) paint based on polyurethane (PU) binder applied on a copper substrate [13,14] was tested with regards to its thermal stability. Thus, onlypartone oftheALTmethodwas exercised. Tests that cover the long-term stability with regards to high humidity and condensation (part two) and atmospheric corrosion caused by sulfur dioxide (part three) have not been investigated.
