Anti-soiling and highly transparent coatings with multi-scale features

Soiling of optical surfaces due to sand and dust accumulation is the main cause for decreased efficiency of concentrating solar power and photovoltaic installations in desert areas. Nanostructured coatings with tailored surface roughness can reduce the rate of soil accumulation and maintain the high optical performance of the solar mirrors and cover glass. Here, we investigate the correlation between the size and structure of the surface features of the coating and its anti-soiling and optical properties. To control the morphology of the surface features we developed two types of coating: (1) based on small size (30-50 nm) silica particles with nanostructured surface and (2) based on unstructured nanoparticles with bimodal size distribution (80 and 35 nm). We tailored the surface features of the coatings to achieve synergistic improvements over different length-scales and thus decrease the adhesion force between the soil particles and the surface. Adhesion force measurements were performed using atomic force microscopy. The adhesion force and energy required to separate a silica particle from the surface of coated solar glass was significantly lower than the respective values from the surface of uncoated solar glass. A falling sand abrasion test, modeled after the procedure in ASTM D968, was performed. The optical properties of coated and uncoated solar glass were measured before and after the soiling test. Coated solar mirror samples were tested in the field. The results of the field test provided evidence that the anti-soiling coating is effective at reducing soiling and improving the specular reflectances of the coated mirrors. The use of the developed anti-soiling coating can be extended to other power-grid applications where reducing the soil accumulation is valuable.