Estimating global solar radiation from common meteorological data in Aranjuez, Spain

This study aimed to calibrate existing models and develop a new model for estimating global solar radiation data using commonly and available measured meteorological records such as precipitation or temperature. Fifteen empirical global radiation models based on meteorological variables were generated and validated using daily data in 2003-2008 at the Aranjuez station (Community of Madrid, Spain). Validation criteria included coefficient of determination, root mean square error, mean bias error, mean absolute bias error, mean percentage error, and mean absolute percentage error. The best result was derived from the model proposed, which uses extraterrestrial solar radiation, saturation vapor pressures, transformed rainfall data and daily minimum relative humidity as predictors. The new multiple regression relation giving accurate estimates of daily global solar radiation was suggested. It has a high coefficient of determination R-2 = 0.92. The results showed that the suggested model can estimate the global solar radiation acceptable values of RMSE, MBE and MABE (2.378, 0.09767, 1.744 MJ m(-2) day(-1), respectively); and MPE and MAPE (-6.478%, 19.30%). Temperature based models provided less accurate results, of which the best one is the Bristow and Campbell model (R-2 = 0.892). The Hargreaves and Samani model is simple and are recommended to estimate the daily global radiation when only temperature data are available and when the coefficients cannot be determined. Based on overall results it was concluded that the meteorological based method provides reasonably accurate estimates of global solar radiation, for the site where coefficients of the model were developed.