Statistical analysis and modelling of one-minute global solar irradiance for a tropical country

In-depth knowledge and understanding pertaining to the characteristics and short-term variations of solar radiation are essential, to promote the efficient utilization of solar energy. In particular, these findings are beneficial to tropical locations that are geographically positioned at the center of the “solar belt”, due to the abundant and persistent solar radiation encountered throughout the year, albeit limited by the scarcity of relevant research efforts till date. In this paper, we analyze the probability density distribution of the clearness index for short-term variations of solar radiation at the surface, conditioned to the relative optical air mass by employing the one-minute global solar irradiance measured over a one-year period in the tropical location of Sepang, Malaysia. We show that the temporal variability of solar irradiance for the location under study exhibits bimodal behavior, and reveal that the observed characteristics of the density distribution disappear with increasing relative optical air mass. Next, we model the probability density distributions of the one-minute clearness index as a mixture of two normal functions. The parameters taken into account in the proposed model show strong dependency on the relative optical air mass.