Non-fluorinated, anti-reflective, self-cleaning and durable silane based superhydrophobic coating for floating solar cells

Abstract

Floating photovoltaic (FPV) modules are increasingly adopted for sustainable energy generation but their outdoor exposure to dust and environmental pollutants significantly reduces power generation efficiency and increases maintenance requirements. To the best of our knowledge this is first study to report an anti-reflective, fluorine-free, transparent, durable and superhydrophobic coating to the floating solar cells or floatovoltaics. The innovative double layer design features an anti-reflective bottom layer and a superhydrophobic top layer. The anti-reflective layer, covalently bonded to the substrate for enhanced adhesion, incorporates a nanoporous structure with a refractive index of 1.384 enhancing light transmittance. The superhydrophobic top layer, composed of silica nanoparticles on the nanoporous framework achieves a static water contact angle of 158.2 $\pm 0.7°$ facilitating self-cleaning and dust repellence. The coating demonstrated a maximum transmittance of 93.137 % at 582 nm, 3.31 % higher than bare glass. The study also attempts to experimentally calculate the surface free energy over commonly reported theoretical values by using Owens-Wendt method to corroborate the inverse relationship between surface roughness and surface energy which are the fundamental properties of superhydrophobic surfaces. In the self-cleaning test, the coating effectively repelled dust and pollutants including those specific to both freshwater and marine environments of FPV systems. Durability tests revealed strong mechanical and chemical properties, including passing a 3H pencil hardness test, five tape adhesion cycles and maintaining a water contact angle of 147.7 $\pm 1.6°$ after sandpaper abrasion and sand fall impact tests. Additionally, the coating demonstrated superior UVA resistance ensuring suitability for prolonged outdoor exposure. This facile and low cost production method is believed to offer an effective solution enhancing the efficiency of floating solar cells, marking a significant advancement in the field of photovoltaic module surface engineering.