Solar Energy Materials and Solar Cells, Vol.189, 188-196, 2019
Self-cleaning performance of superhydrophobic hot-embossed fluoropolymer films for photovoltaic modules
The soiling of photovoltaic (PV) modules can significantly reduce their energy yield unless a mitigation strategy is employed. One solution investigated in this work involves the implementation of a passive self-cleaning superhydrophobic top cover. To this end, superhydrophobicity was induced by hot-embossing random micro textures on a highly transmissive and photostable fluorinated ethylene propylene (FEP) film. The impact of fabrication parameters (hot-embossing force and temperature) on achieving high contact angles (> 150 degrees) and low roll-off angles (< 10 degrees), which characterizes a surface as superhydrophobic, were investigated. It was found that a minimum threshold force of at least 15 kN and 5 kN must be used to achieve superhydrophobicity for processing temperatures of 270 degrees C and 280 degrees C respectively. Meanwhile at the highest investigated temperature of 290 degrees C, any force within the investigated range of 500 N to 50 kN suffices. The best fabrication parameters were identified (5 kN at 280 degrees C), resulting in a contact angle of 156 +/- 1 degrees and a roll-off angle of 8 +/- 3 degrees. When incorporated into a silicon PV mini-module, the addition of the textured FEP film enhances the short circuit current density (J(SC) by 1.1%. Moreover, the self-cleaning properties of the textured FEP films result in a recovery ratio of 93.6% (in terms of J(SC)), which is significantly greater than that of the reference glass encapsulated PV mini module (61.1%).
Keywords:Superhydrophobic;Self-cleaning;Anti-reflective coating;Photovoltaic;Fluorinated ethylene propylene;Hot-embossing