Wind tunnel protocol to study the effects of anti-soiling and anti-reflective coatings on deposition, removal, and accumulation of dust on photovoltaic surfaces and consequences for optical transmittance

A wind tunnel protocol is presented that allows to study the efficiency of anti-soiling and anti-reflective coatings under dry soiling conditions. Anti-soiling coatings are intended to reduce the accumulation of dust on photovoltaic modules and other surfaces. Dust accumulation is the combined result of sedimentation (or deposition) and syngenetic or post-genetic removal. In the field, the amount of dust present on a photovoltaic surface is always the result of accumulation. The protocol allows one to study the effects of anti-soiling and anti-reflective coatings on the processes of dust deposition and dust removal separately so that the specific operation of the coatings in comparison to uncoated glass can be better understood. Using an aeolian dust wind tunnel, dust deposition and dust removal measurements were performed under quasi-natural conditions on surfaces with and surfaces without an anti-soiling coating. Optical transmittance measurements were performed to determine the impact of anti-soiling and anti-reflective coatings on the amount of light passing through dust-polluted surfaces. We illustrate the protocol by comparing anti-soiling and anti-reflective coated surfaces with identical uncoated surfaces. The anti-soiling coating that was tested in this study has a dual functionality as it has both anti-soiling and anti-reflective properties. Results showed that the tested coatings did not affect the sedimentation of dust, but they did have a significant effect on dust removal, which started at a lower wind speed and cleaned the surface more rapidly compared to the uncoated surface. Additionally, the anti-soiling coating outperformed the anti-reflective coating regarding the wind speed at which dust removal started, indicating that dust adhesion forces on the anti-soiling coating are lower. Transmittance was always higher for the coated surfaces than for the uncoated surface, but the benefit of the coatings (higher transmittance) decreased as the glass surfaces became more polluted with dust.