Effect of dilute acid exposure on sol-gel porous silica anti-reflection coatings

The build-up of algae and moss on the outer glass surface of solar modules causes serious attenuation of the incident light. Biocides are effective in removing this surface contamination to restore performance. These biocides are acid based and there is some concern that their use may affect the integrity of the porous silica anti-reflection coatings (ARC). Here we report on the effect of a commercial biocide treatment on sol-gel porous silica AR coatings. The biocide used was SFC Eco which is already deployed on solar utilities. Our initial studies show the effectiveness of nonanoic acid-based biocide as an algae cleaning solution. The treatment using a dilute solution does slightly etch the morphology of the coating. Similar effects could also be caused by acids in rainfall, so we have also conducted tests using sulphuric, nitric and carbonic acids at similar dilutions. These tests showed that these tests also resulted in similar etching but that there no significant change in the transmittance or reflectance of the coating. Our studies are continuing to investigate if long term exposure to acidic environment or cyclic applications of biocides will cause significant degradation.