Statistical Assessment of Average Global and Diffuse Solar Radiation on Horizontal Surfaces in Tropical Climate

Abstract-The hourly and monthly average global and diffuse solar radiation on horizontal surfaces in Nsukka, a tropical climate on Lat. 6 0 52 ' N, Long. 7 0 24 ' E and 397 metres above sea level, were critically evaluated for each month of the year, starting from November 2009 to October 2010. For each month, the hourly average global and diffuse irradiance obtained were correlated with local time of the day, using second degree polynomials, while the monthly average values were correlated with the months of the year, using third degree polynomials. These correlations were performed to facilitate easy prediction of global and diffuse irradiance at any time and month of the year in Nsukka. The maximum hourly average global irradiance of 773 W/m 2 was observed at 12.00 noon for the month of January 2010, while the minimum hourly average value of 426 W/