This paper introduces a model that quantifies the relationship between power output, incident irradiance and soil particle size composition of soiled photovoltaic panels. Soil samples used in artificial soiling experiments were collected from Shekhawati region in India and their relative percentage of standard particle sizes is determined from sieve analysis. A non-linear relationship between irradiance and power is obtained using regression analysis showing the effect of particle size composition present on the panel. Further, the tilt angle for maximum power extraction is determined for each soiled panel and the deviation from the optimum tilt angle of a clean panel is observed. It is concluded that, when the soil present on the panel is rich in the particles with diameter (75 gm and below), the deviation from the tilt angle of a clean panel is 4 degrees, however if the soil contains higher composition of both 150 mu m and 300 mu m particle sizes the deviation is 8 degrees. (C) 2016 Elsevier Ltd. All rights reserved.