Daily diffuse solar radiation at Beijing

In order to obtain reliable radiation for design, operation and economic assessment of solar energy conversion device, a statistical analysis of daily correlations between diffuse solar radiation and global solar radiation is carried out using 10yr data (1995-2004) of daily global and diffuse solar radiation obtained at Beijing meteorological station of China. The accuracy of the correlations is performed in terms of the coefficient of determination, R². The results indicate that the correlations relating the diffuse fraction (K_d) with the clearness index (K_t) are reliable for diffuse radiation prediction at Beijing, China. And the quadratic model of the whole period is preferred for both its accuracy and its simplicity.