A model to determine soiling, shading and thermal losses from PV yield data

Abstract

Apart from being a clean source of energy, photovoltaic (PV) power plants are also a source of income generation for its investors and lenders. Therefore, mitigation of system losses is crucial for economic operation of PV plants. Combined losses due to soiling, shading and temperature in PV plants go as high as 50%. Much of these losses are unaccounted initially, which can jeopardize the economic viability of PV projects. This paper aims to provide a model to determine losses due to soiling, shading and temperature using quantities like irradiance, cell temperature, DC power and current, which are readily available in PV yield data captured by the remote monitoring system, without involving any additional sensors or equipment. In this study, soiling, shading and thermal losses were calculated using PV yield data obtained from a 30-kWp PV plant located in Kharagpur, India. The results showed soiling and shading losses as high as 25.7% and 9.7%, respectively, in the month of December. Soiling loss was verified by measuring transmittance loss of coupon glasses installed in the vicinity of the plant. Shading loss was verified by shadow simulation using an architectural tool (SketchUp). Array thermal loss obtained using the proposed methodology was found to be in line with the estimated value obtained from PVsyst simulation. Additionally, using time-series data, the energy losses corresponding to soiling, shading and temperature effects were calculated by a numerical-integration technique. The monetary loss due to these energy losses thus obtained provides criteria for deciding when to mitigate the sources of these losses.