Test Methods for Hydrophobic Coatings on Solar Cover Glass

The world market for solar energy continues to expand. However, to be competitive with traditional energy sources, photovoltaic (PV) modules must be capable of continuous and reliable high performance. Performance losses occur due to the soiling of the cover glass on modules. Soiling can be reduced by using hydrophobic coatings. These decrease surface energy and thus minimize adhesion to soiling. These coatings can help reduce maintenance and retain consistent electrical output. It is not yet clear, how hydrophobic coatings can be assessed and compared. In this paper, test methods to simulate the stresses that coatings experience in their life-time are assessed. These test methods help to predict the durability and useful lifetime of the coatings when applied to solar cover glass. Various test methods from different standards have been applied to hydrophobic coated glass surfaces and optimized to simulate real-outdoor conditions. A sand impact test and a water drop simulation test have been devised to study the effect of sand and rain on hydrophobic performance and durability.