Diffuse fraction of daily global radiation at Dhahran, Saudi Arabia

Relationship between the diffuse fraction of daily global solar radiation and clearness index (the ratio of global to extraterrestrial radiation) is obtained from the radiation data measured at Dhahran (26°32′N, 50°13′E), Saudi Arabia. Two years of daily radiation data calculated from measured one-minute values are used to develop the relationship. Another year of data is used to validate the relationship. Comparison between the present correlation and previous correlations is presented. The present data confirm the seasonal dependence and the location independence of the correlation reported in literature. The diffuse and global solar radiation are presented for dusty and clear days. The results show that the dust significantly increases the diffuse fraction of the global radiation. The diffuse fraction on a typical clear day in March is 0.11, while on a dusty day, in the same month, may be as high as 0.91.