PV coating abrasion by cleaning machines in desert environments – measurement techniques and test conditions

As PV cleaning machines become widely adopted in desert regions, there is concern that frequent dry-brushing might abrade modules’ anti-reflective coating (ARC). It is common to study ARC abrasion via accelerated lab tests, which typically differ from real-world PV cleaning regarding sample format, test conditions and characterization tools. This paper reviews research on PV ARC cleaning abrasion, focusing on differences in experimental techniques between the lab and field. The main conclusions are: (1) coupon tests should be verified with full-size modules due to dependence of coating properties on sample size, (2) lab tests should be verified outdoors with non-accelerated cleaning schedules because abrasion is largely caused by the soiling layer itself when brushing, (3) reflectivity is well suited to measuring ARC abrasion because it can be performed in the field and is reasonably consistent with module optical performance, (4) different ARCs exhibit a wide range of abrasion susceptibility whereas bare glass is essentially immune to dry brushing.