Performance of Statistical Comparison Models ...

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. The global, direct and diffuse solar radiation incident on a horizontal surface at Cairo, Egypt (lat. 300 05‟ N & Long. 310 15‟ E), during the period time from January 1995 to December 2005 are used. The regression equations between (G/Go) and meteorological variables along with the values of (MBE), (RMSE), MPE, R2 and the t-test statics are discussed. The linear regression analysis was used to comparison between measured and calculated values of the solar radiation are presented. The Olmo et al. model was applied to the database corresponding to the horizontal solar irradiation to determine values for a south facing surface, 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. Fifth solar irradiance models are considered in this article; the isotropic model, Hay, Klucher‟s, Perez and Tamps and Coulson‟s are anisotropic models at different slope. The RMSEs values for all fifth models increases as the slope of the collector increase but remain in a domain of error for which these relations can be applied with good accuracy. The observation of the Perez‟s and Klucher models describes the irradiance on inclined plane more accurately than anther models.