Evaluation of anti-soiling coatings for CSP reflectors under realistic outdoor conditions

Soiling of solar reflectors affects their reflectance and has a direct impact on the power output of concentrated solar power (CSP) plants. One way to minimize the efficiency losses is the implementation of anti-soiling coatings on the reflector surfaces. This method is being studied for the past decade, but has not been successfully commercialized yet. The purpose of the coatings is to reduce soiling and improve the washability of the reflectors. In this work results are presented from an extensive outdoor campaign of two potential anti-soiling coatings under realistic conditions at a representative CSP site in southern Spain. Nearly six years of outdoor data are available, which makes this campaign the longest published on this type of coatings. Regular cleaning and reflectance measurements were performed during the exposure and conclusions about the performance and durability of the coatings are drawn. It is shown that in the initial state the coatings show an advantageous behavior, resulting in higher reflectance during outdoor exposure due to less soiling and better cleaning of the reflectors. The second main finding is that durability is an important issue for the implemented coatings, as their properties degrade over time resulting in lower reflectance values after several years of exposure compared to conventional glass reflectors.