Cleaning efficacy of anti-soiling coatings

Dust deposition on photovoltaic module can reduce energy generation up to 50% if not cleaned for 4 months in Mumbai, India (warm and humid climate). Hydrophobic (contact angle> 90°) anti-soiling coating (ASC) is a cost-effective mitigation strategy to reduce soiling. In this paper, we compared the cleaning efficacy of 4 different commercial hydrophobic anti-soiling coatings (on solar glass and PV modules) with a not-coated sample. All coated glass samples (A, B, C and D) showed higher cleaning efficacy (lower soiling loss) than the not-coated glass sample after cleaning with a 45 µl deionized water droplet. This was also confirmed by field exposure study done on PV modules (for coating B,C and D). Cleaning efficacy of the coating D (on PV module) decreased significantly after 2nd manual cleaning run, indicating abrasion caused by the cleaning tool, implying that the selection of cleaning methods/tools is critical. Under controlled environment (on solar glass) cleaning efficacy of all coated glass samples reduced by a factor of 6 (average) as the rolling water droplet travels from top to bottom, covering a total distance of 3.6 cm, This is due to the reduction in speed of the water droplet rolling off the surface as it accumulates more dust. Roll of angle for clean coated glass increases by a factor of 2 (for coating A,C and D) when measured on dust deposited glass substrate, indicating that roll-off angle depends on the surface of the ASC coatings, which may vary with exposure time and environmental conditions like soiling rate. Ranking of cleaning efficacy of ASC under field exposure correlated well with the roll-off angle measured on soiled samples in controlled experiments. This suggest roll - off angle as an important measure for the evaluation of the anti-soiling coatings.