Further investigation of empirically derived models with multiple predictors in estimating monthly average daily diffuse solar radiation over China

Two models based on Li et al. (2011) are developed for general application in estimating the monthly average daily diffuse solar radiation in China. The validation of these models is performed by comparing with four existing empirical models against the measured data. It is found that the proposed models have better performance than these existing models. This study further argues that ambient temperature and relative humidity incorporated into empirical models can generally improve its estimates. Hence, the two models can be recommended for general application in estimating the monthly average daily diffuse solar radiation in China. ► Two general models with multiple predictors are proposed for estimating monthly average daily diffuse solar radiation. ► Predictors include the clearness index, relative sunshine duration, ambient temperature and relative humidity. ► The models are validated at 17 first-level stations in China covering a diverse range in climate and geography. ► Ambient temperature and relative humidity included into empirical models can generally improve the estimates.