A GENERAL EMPIRICAL MODEL FOR ESTIMATION OF SOLAR RADIATION IN YANGTZE RIVER BASIN

Solar radiation is the principal and fundamental energy for many physical, chemical and biological processes. Estimation of solar radiation by Ångström-Prescott (A-P) model from sunshine duration is common employed. In this paper, the original linear A-P model and four commonly used modification models (quadratic, cubic, power and logarithmic functions) are comparatively studied. It is found that the linear, second and cubic models give very similar goodness of fit, and the linear model is recommended due to its greater simplicity and convenience. The A-P model parameter a, sum a + b correlate most significantly with altitude. Based on these correlations, the deterministic equations of parameters a and b are proposed. Consequently, the A-P model with the estimated parameters by deterministic equations is used to estimate solar radiation, and it gives good performance with the RMSE < 1.7 MJ m -2 , RRMSE < 20% and R 2 > 0.89. It is therefore recommended to use these equations to determine the A-P parameters in Yangtze River basin in China, and it is believed particularly useful for the site where lacks of the measured solar radiation data for calibration.