Evaluation of transposition models of solar irradiance over Egypt

The main objective in this paper is to carry out evaluation of statistical comparison of the monthly hourly and the daily data of global, beam and diffuse solar radiation incident on a horizontal and inclined surfaces for Cairo, Egypt during the period time from 1984 to 2014. The maximum and minimum values of correlation coefficient (R2) are 0.994 and 0.968 according to Eqs. (13), (15) respectively. The comparison between the measured (Gd,m) and calculated (Gd,c) values of the diffuse solar radiation along with the values of mean base error (MBE), root mean square error (RMSE), mean percentage error (MPE), and t-Test statics are summarized. The values of MBE results show that the isotropic, Perez's, Hay's and Klucher's models are substantially under predicts the irradiance incident on an inclined surface, and the Tamps and Coulson model considerably over predicts irradiance incident on an inclined surface on an overall basis, and 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. In general we confirm that, the observation of the Perez's and Klucher models describe the irradiance on inclined plane more accurately than anther models. These results in the present work are good agreement with other work in [9,12,129,130] (Khalil and Shaffie, 2013a; Khalil and Shaffie, 2013b; Khalil and Shaffie, 2014; Khalil and Shaffie, 2016). The statistical results of the models for south facing and west facing surface in the present study are analyzed.