Modeling Solar Radiation at the Earth Surface

The aim of this chapter is to describe algorithms for estimating the amount of solar energy incident at ground level on horizontal and inclined surfaces as well as on sun tracking surfaces. First, a general algorithm for estimating the solar irradiation on tilted surfaces is summarized. Next, models are presented for, respectively, the calculation of extraterrestrial radiation, quantification of the atmosphere effect on extraterrestrial solar radiation, calculation of solar irradiance on the horizontal plane, and transposing the result on tilted planes. Some of these models may be included within the procedures for forecasting the solar resource. Simple models may be used for straightforward prediction of solar irradiance and irradiation on horizontal surface under clear sky conditions. For more demanding applications, parametric models are the alternative. Basically, this is feasible by employing forecasted meteorological parameters as model inputs. For adjusting clear sky solar irradiance to the forecasted state of the sky, a survey of the required equations is presented.