Optical damage tests on reflecting materials for solar applications

Concentrated Solar Power and Concentrating Photovoltaics usually involve secondary optics that collects the sunlight focused by the primary optic to improve system energetic performance. Promising materials for the construction of secondary reflectors for a solar furnace were tested, examining endurance at the working power density and verifying if an achievable damage threshold exists. The field test consisted in exposing the samples to sunlight by using a dual-axis solar tracker and a suitable Fresnel lens. The materials were glass mirrors and a multilayer mirror based on an aluminum substrate. The measured quantities were: systematic reflectance control; temperature of the sample back side; concentrated solar power density; exposure time. The samples showed no appreciable decays in reflectance during the whole exposure period.