ABSTRACT
Estimating the solar radiation on inclined surfaces such as those involved in the design of solar panels for energy harvesting is rather complex and difficult. Factors such as circumsolar aureole brightness and horizon brightening as well as variations in the foreground albedo of a tilted surface contribute to this complexity. The simplifying assumption of a relatively uniform (isotropic) radiation field can be used to produce simple equations for estimating the diffuse irradiance available to a nonhorizontal collector. The isotropic models described usually overestimate the available radiation for a tilted surface. The Perez anisotropic model produces the estimated diffuse irradiance on a tilted surface based on three modifier terms to the total hemispherical diffusion, diffuse horizontal irradiance (DHI). The accuracy of the Perez anisotropic model has been evaluated by both the original authors and many other writers over the more than 20-year lifetime of the model.
