Abstract <p>Mathematical models for calculating the average daily solar radiation are considered. The scattered solar radiation method is shown to feature the smallest calculation error. The calculation methods proposed for mobile and stationary photovoltaic panels make it possible to enhance the accuracy of forecasting the electricity generation by solar plants. The error of the considered mathematical models as applied to the conditions of Orenburg turned out to be acceptable for engineering calculations. Compared with existing forecasting methods, the proposed approach enabled an increase in the accuracy of calculations by more than 30%, which yields more accurate estimates of the payback period of the installed equipment. The selected methods can be used in the development of automated design systems for solar plants and verification calculations.</p>