Dust settling on the surface of the photovoltaic module (PVM) forms a film that absorbs part of the solar radiation flux, as a result of which the volume of generated electric energy decreases. An effective method for cleaning the surface of the PVM from contamination should be based on knowledge of the fundamental properties of dust and an understanding of the contamination processes. In this paper, a mathematical model of the contamination of the PVM surface is proposed. It was found that the soiling of the PVM surface depends on the dynamic viscosity and the velocity of the convective air flow. The convective air flow separates dust particles by size. If the convective flow velocity is less than 4 cm/s, then particles with a radius of 50 μm and less do not settle on the surface of the PVM. It is shown that a vertically located PVM retains dust particles with a radius of 50 to 70 µm. The wind speed and direction, the temperature of the PVM, the condition and structure of its surface have a significant impact on contamination.