Simplified Set-Up for Near-Specular Solar Reflectance Measurement

Abstract

In Concentrating Solar Power (CSP) plants, mirrors are used to redirect solar radiation onto a receiver. More precisely, the solar radiation, diverging with a half-angle of about 4.7 mrad, impinges off-normal on the mirror. Only the radiation reflected within the acceptance angle of the receiver is geometrically intercepted. Therefore, the kind of reflectance relevant for CSP applications can be defined as “near-specular”; it depends on three angles: solar-divergence, incidence on the mirror and detector-acceptance. Actually, the market is lacking of instruments to properly measure the near-specular reflectance. For that purpose only one custom instrument was set-up at a highly specialized laboratory to measure the spectral near-specular reflectance for both clean and soiled mirrors; in the latter more radiation is reflected beyond the acceptance angle. Now, the Work-Package 4 of the “Recommendations for reflectance measurements on soiled solar mirrors” Project funded by SolarPACES aims to cover that gap by outlining a Simplified Set-Up (SSUp) based on commercial components. It can be replicated by anyone having just basic skills in optics. The concept could even be taken by an industrial player to commercialize an engineered version of SSUp.