Abrasion of PV Antireflective Coatings by Robot Cleaning

The growing use of photovoltaic (PV) cleaning machines ("robots") raises the risk of abrasion to the antireflective coating (ARC) on modules' front glass. ARC abrasion is often studied via accelerated lab tests, however field tests are needed to achieve real-world abrasion conditions. In this study nine types of PV modules and five types of ARC coupons were subjected to 18 months of dry-brush robot cleaning in the desert climate of Doha, Qatar. Three cleaning schedules were tested: daily, weekly, and never (reference samples subject to weathering alone). Modules' power (Pmax), current (Isc), and reflectivity changes were measured and compared between the various cleaning schedules. It was found that the abrasion resistance of PV modules varied greatly. Five kinds of module showed greater losses with more frequent cleaning, while the other four did not. Lab profilometry of the coupons similarly found large variability of the depth and quantity of scratches for different ARCs, because of the difference in ARC durability between modules, and the likelihood that different cleaning robots will vary in their harshness, it is recommended to test specific robot/module pairs in the field to be confident of their ARC degradation rate.