Comparison of Seven Empirical Models For Estimating Monthly Global Solar Radiation, (Case Study: Libya)

The aim of this study is to compare seven empirical models to find out which of them is the most efficient for estimating monthly global solar radiation. 3-years period data (2018-2020) used for the comparison were collected using automatic weather station installed at the Libyan Center for Solar Energy Research and Studies site, Tripoli, Libya (Lat. 32.815 N, Long. 13.439 E). The least square method is used to establish the models and determine their empirical coefficients. In order to evaluate the performance of the established models, three statistical error tests were introduced, root mean square error, RMSE, mean absolute percentage error, MAPE, and correlation coefficient, R2. The obtained results indicated that the weather condition is fair during May-September, and scattered clouds during the other months. The results also indicated that the sunshine duration-based quadratic model presented the best efficiency for estimating the monthly average of daily global solar radiation on a horizontal surface, where it had the highest value of correlation coefficient, and the smallest values of MAPE and RMSE of 0.93, 2.8049, and 0.0195 kWh⁄m2 ⁄day, respectively.