Characterization of Sky Conditions Using Clearness Index and Relative Sunshine Duration for Iseyin, Nigeria (Published)
The global solar radiation and sunshine duration data collected over a period of 8 years (2000 – 2007) was examined. The mean monthly clearness index and sunshine duration was calculated and used to develop an Angstrom- page equation for the region. It was observed that the equation has a high correlation coefficient, which gives good results when it was tested with statistical indicators of MBE, MABE and RMSE. Statistical analysis of monthly clearness index showed that the sky conditions at Iseyin were most of time partly cloudy (partly cloudy sky occurred in eight months of the year which is about 66% most of these months falls in the rainy season months). Cloudy sky was only noticed in the month of August which is about 8% and it occurs at the peak of the rainy season. The region has three months of clear sky which is about 25% of the months of the year and they are months in the Harmattan period. The prevailing sunshine condition in Iseyin is predominantly scattered clouds sky except during August and September where a cloudy sky condition is experienced.