Effect of Soiling on the PV Panel kWh Output

Abstract

Ever since the commercial growth of PV installations, soiling has been a crucial factor to decrease its performance ratio. Environmental factors such as irradiation, wind, rainfall, and back module temperature affect the yield of a system, but, in many environments, soiling of PV modules carries the largest impact. Cost effective soiling measurements within a production area can provide reliable insights into the soiling behavior and allow developing an optimal cleaning schedule.

The deposition of dust, soil, and microfibers resulting from the surroundings as well as the growth of minute pollen like moss and fungi are categorized as PV module soiling. It is a lesser acknowledged factor that significantly reduces the power production by acting as a barrier for effective light photons utilized by a module. The estimated loss in the irradiance and power can be determined with the help of a soiling ratio (SR) parameter, which is the ratio of short-circuit current (Isc) or maximum power produced (Pmax) by a soiled module to the clean one.

The first step to address this issue was to analyze the different soiling effects on a module. Various outdoor and indoor soiling experiments were carried out in the rooftop PV system to examine the angular dependency, inhomogeneity, optical losses, and color impacts of the dust. Another aspect of this research project was the development of a novel soiling detection system, the DustIQ. The two sensors with the help of on-board mini-PV module measure the soiling ratio of a soiled module. A wide range of dust color test was also carried out for the color calibration of the sensor. This report also introduces an empirical equation based on incident angle modifier (IAM) for soiled and cleaned PV modules. The proposed equation was used to determine SR over the course of the day for three conditions of high, medium, and low daily average irradiance.

The modeled SR, when compared with the measured data resulted in RMS deviation of ±0.21% on a high irradiance day. Additionally, analyzed soiling behaviors were used to estimate the annual energy loss due to in Delft, The Netherlands. The average irradiance and power loss was found to be 0.083% and 0.165% per day respectively due to the natural accumulation of soil. This resulted in an annual energy loss of 16.22 kWh for a system of 1.62 kWp, considering rainfall (≥ 2 mm) as the only source of module cleaning.