Effect of long term outdoor exposure on anti-soiling coatings for solar reflectors

Results of the outdoor exposure campaign of two newly developed anti-soiling coatings for CSP mirrors are presented in this paper. Samples of coated mirrors were exposed for two years under realistic outdoor conditions and the application of two different cleaning techniques was investigated. Mirror samples were analyzed during exposure and their reflectance and cleanliness were measured. The performance of the anti-soiling coated mirror samples was compared to conventional uncoated mirrors. Depending on the selected combination of coating and cleaning technique, an advantage or disadvantage was observed over the exposure duration. One coating presented an overall cleanliness gain of 0.008 with pressurized water cleaning, due to its superior anti-soiling behavior, while presenting a negative gain of -0.009 with contact cleaning, due to its poor durability. The other coating showed a worse anti-soiling behavior, with a negative gain of -0.005 for pressurized water cleaning, due to its poor washability, and a positive gain of 0.005 with contact cleaning.