Durability of solar reflector materials for secondary concentrators used in CSP systems

Abstract

Secondary concentrators are used in solar concentrating systems to redirect solar beams reflected by the primary concentrators to the focal point or line. These components allow to increase the concentrated solar flux desity and hence to lower thermal radiation losses. Solar reflectors for secondary concentrators are permantently exposed to environmental conditions, high radiation fluxes and evelated temperatures that potentially cause stress and degradation throughout the time. Therefore, analyzing solar reflectors of secondary concentrators by simulating these conditions is curcial. No previous research works about the durabiity of solar reflector materials for secondary concentratos have been reported. The present work is focused on studying the degradation of the reflector materials by siumlating accelerated aging, caused by several ambient parameters and the effect of concentrated radiation.Both cooled and uncoooled systems for secondary concentrators are included in this study. According to results obtained, aluminum reflectors and thin silver-glass refelctros glued to an aluminum structure shoed minimum reflectance losses and structural degradation under the operation conditions of cooled 3D secondary concentrators (tower systems). Following critical aspects to avoid reflector degradation were identified: to select a suitable adhesive material to glue the thin silvered-glass reflector to the support aluminum structure, to properly protect reflectors edges, to design a suitable cooling system and to avoid the combination of high radiation fluxes with mechanical stress. In addition, laminated silvered-glass reflectors have shown to be suitable for uncooled 2D secondary concntrators (Fresnel collectors)- Furhtermore, a comparison with naturally aged secondary concentratros using silvered-glass reflectors glued to an aluminum structure revealed that the simulated degradation under accelerated conditions performed i´n this work did reproduce the most frequent degradation patterns suffered in real operating conditions.