Estimation of global solar radiation using clear sky radiation in Yemen

In this communication, the usability of clear sky radiation for predicting the average global solar radiation has been investigated. For this aim, the various regression analyses were applied by using S/S o and S/S nh parameters. Also, equations which represent the two periods of the year, winter and summer, were developed by using these parameters. The equations developed by using S/S o and S/S nh have approximately the same results. Having the better values of the equations developed by using the change of summer and winter is another result. In addition, the use of the RMSE and MBE in isolation is not an adequate indicator of model performance. Using the t-statistic method and the harmony of results obtained with each method prove that the results are reliable.