Studies of specular reflectance distribution for aged or degraded solar mirrors
One of the key challenges for the CSP industry is to offer high-performance solar mirrors lasting two or three decades, at the lowest cost. For CSP, the performance criteria must include a high solar reflectance (up to 90%) with high specular reflection, i.e. the solar flux must reflect with an acceptance angle as small as possible. In this study, we have compared the reflected power distribution (the acceptance angle) of different commercial solar mirrors: new, soiled or natural and artificially aged. The measurements were performed using VLABS setup, at the Fraunhofer Institute in Germany. The objective is to make sure that different levels of ageing or soiling on the mirrors do not alter the power distribution, depending on the aperture angle. We conclude that all mirrors tested are good candidates. The analyses show that soiling or ageing do not alter the size of the specular reflection spot. All degraded, soiled and/or aged mirrors are able to focus the sun light with the same concentration ratio than new mirrors.