Performance of Statistical Comparison Models of Solar Energy on Horizontal and Inclined Surface

Solar radiation data are essential in the design of solar energy conversion devices. In this regard, empirical models were selected to estimate the solar radiation on horizontal and inclined surfaces. We used in this article eleven years of solar radiation over Cairo, Egypt from 1995‐2005, and usedthe statistical parameters ((MBE), (RMSE), MPE, R^2), and t‐Test statics, in order to differentiate among these models and choose the best model. The Olmo et al. model was applied to the database corresponding to the horizontal solar irradiation to determine values for a south facing surface, and Olmo et al. model is recommended to estimate the global solar radiation on an inclined surface in this study, due to its accuracy, input requirements and simplicity. The RMSE results indicate that the anisotropic models (Hay, Klucher and Perez) show similar performance on an overall basis, but isotropic model and Tamps and Coulson exhibit much larger error. Generally, the observation of the Perez's and Klucher models describes that the irradiance on inclined plane is more accurate than that in other models.