Effects of Soiling of Photovoltaic Modules and Systems in Brazil’s Climate Zones

This work reports a methodology for quantifying soiling loss in photovoltaic (PV) modules. We use measurements from c-Si and thin-film CdTe soiling stations installed in Belo Horizonte (19.92° S, 43.99° W), Porto Alegre (30.05° S, 51.17° W), and Brotas de Macaúbas (12.0011° S, 42.6303° W) in Brazil to example and validate this analytical approach. The measured PV module electrical parameters are compared with precipitation data collected in the same location, with the objective of evaluating the behavior of the soiling ratio during the dry periods. Mathematical models determined the soiling ratio (SRatio) and soiling rate (SRate) for each site (in compliance with the IEC-61724-1 monitoring standard [1]). The SRatio for short-circuit current and maximum power data from the modules were evaluated and compared, characterizing the potential effects of uniform and non-uniform soiling. The SRate defines the fraction of the ratio of soiling per day during the dry period (no rainfall). In addition, a method for analyzing energy-production data of PV systems in order to extract the soiling rate was developed and used to compare with monitoring system data. The soiling gravimetric densities (g/m²) were determined using the modeling by Coello and Boyle [2] and Hegazy [3] and these are compared to data collected using the Figgis soiling microscope [4].