Interrelationships Among Non-Uniform Soiling Distributions and PV Module Performance Parameters, Climate Conditions, and Soiling Particle and Module Surface Properties

Soiling of PV modules is a growing concern because of the derating of energy output from solar installations, especially in the growing markets in the sun-rich areas of the world that ironically also might have the greatest issues with dust accumulation. This paper examines the relationships among soiling levels and PV module performance, the climate conditions, and the physical and chemical properties of the soiling particles and surfaces involved. Specifically, these studies focus on the commonly encountered non-uniform soiling of module surfaces. These non-uniform accumulations not only cause decrease in the power produced, but result in shading that can cause increased area heating (“hot spots”) leading to module degradation. This paper evaluates the effects of non-uniform soiling patterns (categorized as edge build-up, waves, and blotches) on the J-V characteristics, documenting changes in the shape of these characteristics with the geometry and thickness distributions on the module surfaces. These studies are performed on crystalline Si framed modules and thin-film CdTe frameless modules. The nonuniform distributions are also related to the temperature distributions-with the temperature mapping evaluated using IR cameras. Hot spots with temperature increases of more than 15°C in some cases for modules operating under normal sunlight conditions. These soiling patterns, performance parameters, and temperature distributions/levels are determined for modules in several Brazil climate zones-although some results are compared to cases evaluated from the other world geographical regions. The soiling patterning is due to primarily wind, moisture. In some cases, the adhesion of the particles can be correlated with the modules surface conditions and the corresponding chemistry of the particles under the specific climate conditions.