Degradation of concentrating solar thermal reflectors in acid rain atmospheres

Abstract

Given the importance that concentrating solar power technologies have had in recent years, the interaction between humid atmospheres in which SO2 is the main pollutant and the metal reflecting layers of the solar concentrators is a major concern that should be addressed. Previous durability studies have urged the importance of designing an accelerated aging test protocol for simulating aggressive industrial atmospheres that solar reflector materials are bound to encounter. Therefore, three types of reflectors were tested in an acid-rain (or Kesternich) chamber at various temperatures and gas concentrations based on the DIN 50018 and ISO 6988 standards. The results showed the significant effect of high SO2 concentrations rather than high temperatures on silvered-glass reflectors, although synergy should not be disregarded. Strong reductions in specular reflectance were found for one type of silvered reflector compared to another type, highlighting the significance of material processing and its effects on their final performance. Aluminum reflectors were not damaged as much as silvered-glass reflectors, but under microscopic inspection, a wide range of noticeable corrosion defects could be found in all the materials. Comparisons between the most representative Kesternich test and samples from an outdoor industrial site permitted realistic lifetime correlations for commercial silvered-glass reflectors.