New equipment for measurement of soiling and specular reflectance on solar mirrors

Abstract

During the life time of Concentrated Solar Power (CSP) plants, optical performance of solar mirrors is affected by soiling phenomena and surface degradation. It is imperative to dissociate soiling that requires cleaning from irreversible degradations which affect the plant performance. In both cases, small degradations or dust deposition cause an optical reflectance loss. In order to provide an adequate cleaning strategy, operators need to determine soiling-induced performance loss. Several commercial instruments already exist to measure optical reflectance, but they are dedicated to a single wavelength range or angle, punctual measurements or to laboratory analyses. CEA has developed a new kind of laboratory sensor to measure separately the loss of reflectance due to the degradation and soiling, thanks to a CCD camera and photodiodes. This equipment allows addressing variable wavelength, incidence and acceptance angles, to compare specular and hemispherical reflectance from other devices. The analysis of the images will quantify the soiling rate in order to optimize the frequency of cleaning water operations. The aim of the present contribution is to distinguish soiling from degradations (abrasion or corrosion of the reflective layer). This paper reviews the different current research works on prototype instruments and a comparison of this new alternative instrument with available commercial ones.