干旱区生态环境知识资源中心

Surface wear of mirrors used in Concentrated Solar Power Plants -CSP- is among phenomena that causes irreversible specular reflectivity losses and therefore, a decrease in the global performance of the plant. This phenomenon can be caused by mechanical contact cleaning or by direct impact by airborne sand particles. In order to evaluate the effect of desert environment on direct surface wear upon mirrors, second surface silvered glass mirrors were exposed in Moroccan desert site, near to Ouarzazate city. In addition and in order to focus on the effect of surface wear separately from other potential degradations, tests were made on sandblasting machine in controlled environment on laboratory. The originality of the present work is that the adjustable parameters were chosen according to global analysis made on climatic and geological parameters of the desert site. Sand particles used in these tests are representatively extracted from the natural site. The application of the outdoor parameters upon mirrors tested on laboratory gives strong similarity of the laboratory's obtained results with those observed during natural aging.

Results of laboratory's simulation tests show that the surface wear increases by increasing the impact velocity and the sand particle size which lead to a decrease in mirror's specular reflectivity.

According to the effect of the impact angle on this phenomenon, it was shown that a glass surface mirror present a maximum surface wear at normal impact angle (90). However by analyzing the results collected from the natural aging tests, it was concluded that surface wear phenomenon was not enough pronounced on the natural aging site after more than 360 days of outdoor exposure.