Outdoor testing of anti-soiling hydrophobic coatings: Observations of cementation

It is of an increasing interest for the solar research community to understand and master the effects of environmental conditions on photovoltaic (PV) module performance and reliability. This study demonstrates that soiling is not only an issue for PV installed in dusty and dry regions of The Middle East and North Africa. Soiling is a global problem and the type of soiling and its extent is dependent on the geographical location. Cementation, a process by which particles strongly adhere to the surface, has been observed on all surfaces exposed outdoors in a coastal location of Denmark and experiments are ongoing in two different geographical locations and climates. Applying hydrophobic coatings to PV module cover glass is a potential solution to minimize soiling. Although the use of a hydrophobic coating was initially effective, its gradual degradation was linked to the build-up of surface cementation. Degradation of the hydrophobic surface chemistry increases surface energy and leads to the formation of hard to remove cementation. This results in the retention of droplets and particles causing a reduction in the optical transmission into the module.