Advanced performance testing of anti-soiling coatings - Part I: Sequential laboratory test methodology covering the physics of natural soiling processes

The accumulation of dust and dirt on PV modules can cause significant energy yield losses, especially in dusty environments. The application of anti-soiling coatings (ASC) is seen as a promising mitigation approach to reduce cleaning frequency and thus cleaning costs. In order to examine the effectiveness of coatings, outdoor tests are usually necessary, but these are subject to varying and complex weather conditions. Therefore, an advanced laboratory soiling test setup and corresponding sequential testing procedures representing the underlying physics of soiling and self-cleaning processes were developed, aiming at fast, reliable and standardized evaluation of the anti-soiling performance of glass coatings. The methods include the control of important environmental parameters during dust deposition and a controlled dust removal by utilization of wind blow or centrifugal forces. Besides method evaluation experiments, comparative soiling experiments were performed for uncoated solar-grade float glass, an anti-reflective coating (ARC) and an ASC. The dusts used for the tests were collected from PV modules located in Dunhuang (cold desert climate, China) and Doha (hot desert climate, Qatar). For sample characterization and soiling loss determination, optical transmittance and light microscopy measurements were performed. Both wind blow and rotational force test (RFT) procedures reveal a reduced dust accumulation for the ARC and a further increased anti-soiling behavior for the ASC. The presented test results are consistent with other outdoor and laboratory soiling studies. Compared to wind blow testing, the rotational force test setup significantly improves the controllability of test parameters and provides a better selectivity of coating performance.