Estimation of horizontal diffuse solar radiation with measured daily data in China

Three most widely used diffuse radiation models are calibrated using the daily data between January 1 1994 and December 31 1998 from 16 stations all over China. The second-degree polynomial relationship between R-D/R-G and n/N (Iqbal model) is suitable for diffuse radiation estimation in China. The averaged correlation coefficient R-2 is 0.84 and the maximum value is 0.93 at the 16 stations, and the Iqbal model works better in the eastern part of China than in the west. The A.A. El-Sebaii model could not be used to estimate diffused radiation accurately in China, with an averaged R-2 = 0.47. The Liu and Jordan model could also be used for diffuse radiation estimation in China, and the averaged value of R 2 and parameter X-0 is 0.81 and 0.233, respectively. There is an evident linear relationship among the parameters X-0, a and b of the Liu and Jordan model. (C) 2003 Elsevier Ltd. All rights reserved.