Sol-gel coatings for solar cover glass: Influence of surface structure on dust accumulation and removal

Soiling of solar cover glass is a major cause for efficiency loss of solar photovoltaic modules. Anti-soiling coatings can be used to reduce the rate of soiling and lower cleaning costs. The efficiency of these coatings has been demonstrated in laboratory and field tests, but the mechanisms and relevant parameters are still not well understood.
In this article, we present a study on the influence of surface structure of hydrophilic sol–gel coatings on their anti-soiling performance in terms of both, dust accumulation and subsequent indoor tests for dust removal by wind. The surface structure of the films originates from the addition of colloidal silica particles of different sizes to the sols used for film preparation. In the dust deposition experiments, standardized test dust and dust collected from solar installations were used. Repeated tests were conducted under controlled humidity.
In the case of dust deposition, the accumulation of dust particles larger than ∼10 µm is strongly reduced, in relation to bare glass, by the anti-soiling effect of all coatings regardless of their surface structure.
For the dust removal via wind, coatings that bear a smoother surface structure are cleaned more easily than coatings with a rougher surface structure.
Additionally, larger and rounder dust particles are removed more easily from coatings with a rougher surface structure (structure height over ∼40 nm), while smaller and more irregularly shaped dust particles are removed more easily from coatings with a smoother surface structure.