Degradation types of reflector materials used in concentrating solar thermal systems

Reflector materials for concentrating solar thermal (CST) technologies must preserve high quality properties (in terms of solar specular reflectance) over the complete lifetime of the solar system. However, these solar components are exposed during their operation to a combination of ambient agents that provokes a number of different defects that might severely curtail their quality. To avoid significant failures, durability studies are being conducted both in outdoor and accelerated aging conditions. The identification of the possible degradation of solar reflectors is thus a key issue for the feasibility of a CST system. This review paper presents a survey of the durability tests most commonly used (mechanical abrasion/erosion, humidity, temperature, thermal cycling, UV radiation and chemical agents), as well as the main degradation types reported in the literature for different reflectors materials (erosion, abrasion, stains on the glass, metal corrosion, tarnishing, cracking, delamination, decohesion, blistering, yellowing, discoloration, haze, agglomeration, diffusion, chalking, etc.). In addition, some defects recently identified are revealed in this publication for the first time. The results shown comprise a useful tool for the interpretation of further durability studies.