Functionality and performance tests for coatings on glass for solar application

Solar glass is widely used as a glazing for solar devices like photovoltaic modules and solar-thermal collectors. Different surface structures and anti-reflection coatings are applied for the increase of the annual gain of solar systems. These surfaces are target for dust accumulation especially at sites which are most attractive for solar systems. Hence the spectral active surfaces lose the functionality due to soiling effects. Former publications showed extreme efficiency losses due to soiling, up to -80% in 6 month. Therefore anti-soiling coatings are offered which promise to reduce these losses. We developed a method for testing the functionality of such coatings by reproducible soiling: surfaces are moistened and homogeneously dusted using a standardized dust. In addition samples are characterized by measuring the change of the spectroscopic properties and the wettability. Each soiled sample is then attached to the specially designed soiling sensor and its performance is monitored at our outdoor weathering test site in Freiburg for several weeks. To test the functionality and natural self-cleaning effect natural rain was awaited. Results show that the soiling effect can be mitigated and the initial transmittance of the solar glass restored in dependence of the rain capacity. Results and tests are transferable to glass for building applications. Prospectively further testing will be done to understand the mechanism of soiling and the reliability of anti-soiling coating in solar applications.