Comparison of Some Existing Models for Estimating Monthly Average Daily Global Solar Radiation for Isparta

The amount of global solar radiation and its temporal distribution are the primary variables for designing solar energy systems, such as flat-plate collectors, photovoltaic systems and other solar energy collecting devices. Knowledge of these parameters is essential to architects and engineers for energy-efficient building designs and solar energy applications. However, direct measuring is not available in many cases, so numerical technique becomes an effective alternative to estimate global radiation through observed meteorological data. In this study, some empirical models in the literature for determining the monthly average daily global solar radiation on a horizontal surface for Isparta were investigated. The models were compared on the basis of statistical error tests using the relative percentage error (e), coefficient of determination (R2), mean percentage error (MPE), mean absolute percentage error (MAPE), the sum of the square of relative error (SSRE), the relative standard error (RSE), mean bias error (MBE), root mean square error (RMSE) and t-statistic (t-stat) method. According to the results, Model 18c showed the best estimation of the global solar radiation on a horizontal surface of Isparta by means of the e (1.77%), R2(95.86%), MPE (0.127%), MAPE (8.95%), SSRE (5.22%), RSE (0.007%), MBE (0.092%), RMSE (1.39%) and t-stat (0.812%). The most suitable model for estimating global solar radiation coming on horizontal surface of Isparta is obtained with Model 18c.