Models for the Calculation of Diffuse Radiation on Solar Collectors

Abstract

For the design and exploitation of solar energy systems, information of both direct and diffuse component of solar radiation is necessary. However, the measurement data that are available are usually restricted to total horizontal irradiance. Therefore, many models have been developed to determine the diffuse component of the irradiance on solar collectors. This paper discusses the most well-known isotropic and anisotropic models for the calculation of the diffuse component of the solar irradiance. A modification of the isotropic clear day model for determining the diffuse component of solar radiation on a horizontal surface has been presented. The presented model has the same form as a simple clear day model, with the parameters determined using the least squares method and measurement data on horizontal irradiance in the region of Belgrade, Serbia. The applicability of isotropic clear day models was examined. The paper also discusses the applicability of the models for determining the diffuse irradiance on tilted collectors in real weather conditions during the year. The basic expressions are given and the characteristics of individual models are highlighted. Based on the measurement data on horizontal irradiance, the possibilities of applying different models for the calculation of the diffuse component of irradiance on solar collectors located in the region of Belgrade were examined.