Guidelines Accelerated Aging Testing of Aluminum Reflectors for Concentrated Solar Power

Abstract

This testing guideline specifies the recommended accelerated aging conditions to reproduce realistic degradation mechanisms on aluminum reflectors, which have been observed during a 3 year outdoor exposure testing campaign at 9 exposure sites with 9 different aluminum reflector types (7 of them protected with a SiO2 based sol-gel coating, 2 of them protected by a polymeric coating). Accelerated aging parameters have been derived to simulate the exposure after 3 and 10 years at three reference outdoor scenarios: “extreme desert”, “desert” and “coastal”. The parameters have been achieved by averaging the 9 tested material types. However, if the material to be tested deviates significantly in its chemical composition, it is likely that other degradation mechanisms will be accelerated and the correlation to the outdoor reference scenarios will not apply. Fig. 1 shows the materials to be tested under the scope of this guideline. In any case, the indicated correlation to the outdoor reference scenarios can only be considered as an estimate. For some of the 9 tested materials the correlation applied better than for others. The expected uncertainty is 4.4 % (pp) specular reflectance, ρ, at a wavelength, λ, of 660 nm, an incidence angle, θi, of 15° and an acceptance angle, φ, of 12.5 mrad to simulate 3 years of exposure on the desert and coastal sites. For the “extreme desert” site the expected uncertainty is considerably higher because of the strong dependence on specific abrasion effects on site. The simulation of 10 years of exposure is based on extrapolation of the available outdoor data after 3 years.