Sand erosion on solar reflectors: Accelerated simulation and comparison with field data

Solar reflectors for concentrating solar power applications can be subject to performance losses due to their permanent exposure to the environment. There is still lack of experience regarding the destructive effects of sand and dust storms on reflector materials and no accelerated ageing guideline is formulated yet to account for the performance loss of solar mirrors due to particle erosion to a realistic extent. The work described here shows one approach to design an accelerated ageing test setup that simulates erosion processes on solar reflectors based on DIN 52348 standard. Furthermore, the results of the developed laboratory ageing method were compared with the effects on exposed outdoor samples from Zagora (Morocco). Laboratory experiments demonstrated a linear correlation between the amount of sand, which is used to erode the reflector samples and their specular reflectance loss. As well, the dependence of the impact angle on the severeness of erosion was investigated. The results are in agreement with earlier works where it was determined that erosion damage on brittle materials like glass is most pronounced for perpendicular impact and becomes weaker for decreasing impact angles. Four different silvered-glass mirrors and three different aluminium mirrors were investigated. Using the results from the laboratory experiments it was possible to attribute defect rates to the respective reflector materials and rank them regarding the resistance towards erosion, specific for this setup. All tested silvered-glass mirrors showed higher erosion resistance than the aluminium samples. The conducted microscope comparison between outdoor exposed samples and those tested under laboratory conditions prove that the developed method for accelerated ageing tests provokes realistic erosion damage. (C) 2015 Elsevier B.V. All rights reserved.