Comparison of Dust Deposition Reduction Performance by Super-Hydrophobic and Super-Hydrophilic Coatings for Solar PV Cells

Dust deposition on solar photovoltaic (PV) cells will dramatically reduce the photovoltaic power output. Self-cleaning coating may be a novel method to decrease dust deposition problems. This paper compares self-cleaning performances and mechanisms of super-hydrophobic and super-hydrophilic coating on dirt deposition decrease for solar photovoltaic cells by experimental measurement. In the process of the deposition of dust on solar cells, covering glass, coated and uncoated, is conducted under natural settling conditions. Moreover, the dust removal efficiency of the glass samples with and without coatings is studied under water spraying conditions. The wettability of different surfaces, dust deposition mass, dust removal efficiency, self-cleaning mechanisms, and transmittance of glass samples are investigated and analyzed. Under natural settling conditions, the deposition mass reduction ratio by the super-hydrophilic coating is only 8.1%, while it can reach 85.8% by the super-hydrophobic coating because of surface micro-structures and low surface energy. However, after the water spraying process, the remaining dust mass ratio for the super-hydrophobic surface is only 16.5%, while it is 18.6% for the super-hydrophilic surface. The self-cleaning mechanism of super-hydrophobic coating is that most deposited particles of dust are removed from glass samples by the rolling of liquid droplets. However, the self-cleaning mechanism of super-hydrophilic coating is the breakup of the liquid film. Therefore, both coatings can effectively reduce dust deposition under water spraying conditions. The average transmittance of super-hydrophobic and super-hydrophilic coatings after the water spraying process is 91.1% and 86.4%, respectively, while it is only 61.1% for the uncoated glass sample.