Durability Testing of Porous SiO2 Anti-reflection Coatings for Solar Cover Glass

Solar photovoltaic (PV) modules experience an optical loss of just over 4% at the front cover glass surface, as a result of the difference in refractive index between glass and air. This loss can be reduced by applying an anti-reflection (AR) coating, and currently over 90% of commercial modules contain a single layer of porous silica (SiO
2
). These AR coating are effective at reducing reflection losses, but have been shown to exhibit poor durability, especially to abrasion caused by module cleaning. In this work, porous SiO
2
coated glass samples have been subject to dry linear abrasion testing, using an Elcometer abrasion tester with a brush and test fixture adapted from a SunBrush, a brush used in industrial module cleaning operations. The coating shows significant degradation in AR performance after abrasion, with almost complete removal after 1000 cycles, with weighted average reflectance (WAR) values increasing from 5.42 % to 7.70 %. A multilayer AR coating with all-dielectric metal oxide layers has been tested alongside the porous SiO
2
to provide a comparison, and shows significantly higher abrasion resistance with very little change in reflectance after 1000 abrasion cycles, offering a durable alternative to the current industry standard.