Estimate of Soiling Rates Based on Soiling Monitoring Station and PV System Data: Case Study for Equatorial-Climate Brazil

Soiling, particulate accumulation on photovoltaic (PV) module surfaces, reduces the available solar resource and the resulting generated device power. In regions where the installation of PV technology is advantageous because of high irradiance areas, in many cases, also possess arid or desert climates that inherently exhibit greater surface soiling. Because of the energy production and associated maintenance-cost factors, it is advantageous to evaluate environmental factors (meteorological variables, climate, and geographical features) as early as possible in developing a PV installation. Alternatively, the determination of the soiling rates (SRate), even after system commissioning can aid in the optimization of maintenance and cleaning-cycle requirements. Significant research has been reported addressing these critical factors through determining local soiling losses. This article presents, evaluates, and compares methodologies to accurately determine and compare SRate and losses from soiling monitoring stations and installed PV systems operating in Belo Horizonte, Brazil (latitude-19.92°, longitude-43.99°). Specifically, data collected from soiling stations were used to estimate the soiling ratio (SRatio) and SRate. A related process is applied to the PV system, using the performance ratio. The methodology incorporates several key refinements. These include normalization and adjustment for the meteorological parameters (temperature and irradiance). Additionally, the differences between the measured global horizontal irradiance (GHI), the plane-of-array irradiance (GPOA) obtained through the application of a transposition model, and the plane-of-array measured by reference cell (Gref) are presented and compared. The results demonstrate that the transposition model is an acceptable option for cases in which only GHI measurements are available.