Advanced performance testing of anti-soiling coatings - Pt.II: Particle-size dependent analysis for physical understanding of dust removal processes and determination of adhesion forces

Soiling is a severe problem for solar energy production. For the development and evaluation of new mitigation strategies such as innovative coatings for PV modules, reliable and realistic test methods are needed. An advanced laboratory soiling test setup and sequential test procedures were used to evaluate the anti-soiling performance of glass coatings. The test method comprises the process of dust deposition by sedimentation in a dust chamber at controlled environmental conditions and two approaches to simulate natural self-cleaning processes by wind, i.e. wind blow testing and rotational force tests (RFT). In order to evaluate the effects of particle rebound during dust deposition and the two different particle removal mechanisms in detail, a physical model including relevant particle adhesion and removal forces is presented. The theoretical analysis shows that the physical processes involved are significantly influenced by particle sizes. Accordingly, soiling test results for uncoated solar glass, an Anti-Reflective Coating (ARC) and an Anti-Soiling Coating (ASC) were analyzed with respect to individual particle sizes and interpreted with the help of the theoretical models. In addition, a statistical approach is presented for determination of coating specific particle adhesion forces from rotational force tests. The newly developed test methods may be used as a practical approach for coating evaluation and future coating development, whereby the presented models and evaluation results for industry-relevant coatings enable a better understanding of particle detachment mechanisms relevant for soiling