Degradation of anti-soiling coatings: mechanical impact of rainfall

Energy loss due to soiling of photovoltaic modules is one of the most reported problems in sunbelt countries. Anti-soiling coatings (ASC) which reduces soiling, offers an economical and universal solution. Since ASC is applied on the outer surface of the PV module, durability of these coatings is essential. In this paper, we compared the field degradation rates of 4 different (named A, B, C and D) commercial hydrophobic ASC in Mumbai, India (warm and humid climate). The degradation rate of ASC was determined in terms of reduction of contact angle per day. Contact angle of one of the ASC changed from hydrophobic to hydrophilic in 5 days of field exposure and all other coatings became hydrophilic in 40 days of field exposure during rainy season. Degradation rates of ASC during rainy season was more than 4 times than that of non-rainy season for all coated samples. Accelerated laboratory tests using acidic water (pH 6) showed good correlation with field exposure for coatings A and C. Laboratory studies on the mechanical impact of rain showed linear rates of degradation for all coated samples, which correlated well with the field exposure study during rainy season. This indicates that the mechanical impact of rain, in addition to the pH and UV exposure reported earlier, as a significant stressor for ASC.