I don't know about cleaning but the desert sand seems to have little effect on the mirrors: "Regarding the irreversible degradation on relative specular reflec

I don't know about cleaning but the desert sand seems to have little effect on the mirrors: "Regarding the irreversible degradation on relative specular reflectivity of exposed mirrors on natural aging site, relative low loss of about 0.4%, on average, was recorded after more than 360 days of exposure. This low degradation can be related to the low wind speed on the region." Surface wear damage of glass solar mirrors in Moroccan desert environment: http://www.researchgate.net/publication/266078057_Surface_wear_damage_of_glass_solar_mirrors_in_Moroccan_desert_environment http://www.researchgate.net/publication/266078057_Surface_we...