VARIATION OF INCOMING SOLAR RADIATION COMPONENTS OVER NIGERIA

Abstract

The aim of this research work is to examine the variation of some solar radiation parameters in Nigeria namely: Global radiation, direct, diffuse radiation, clearness index, direct transmittance and net radiationof four climatic regions in Nigeria. Ten years data of daily global radiation, direct radiation, diffuse radiation, minimum and maximum temperature obtained from the archives of the National Aeronautics and Space Administration (NASA) were used for this study. All solar radiation components investigated show annual variation and seasonal variation while the peaks occur at different time of the year with respect to the solar radiation components. The maximum and minimum mean values of direct solar radiation were 5.259±0.37KWhm-2day-1 in Uyo and 3.260± 0.12KWhm-2day-1. It was observed that the average daily energy input for the whole year in coastal region for global and direct radiations were 8.440±0.33 and 4.963±0.24KWhm-2day 1respectively which agrees with previous works on global and direct radiations distribution in Nigeria. The clearness index ranges from 0.15±0.08 to 0.29±0.09KWhm-2day-1with average value of 0.15±0.06KWhm-2day-1.Theminimum value of the Net radiation, is found to be 1.05± 0.09KWhm-2day-1in the coastal region while the maximum value of 1.38±0.04KWhm 2day-1is noticed in Sahel region. The direct transmittance ranged from 1.05±0.09KWhm-2day-1to 1.38±0.04KWhm-2day-1. The minimum and maximum values were observed in coastal region and Sahel savanna respectively. This finding confirms the similarity in the trends observed in the plots of this work. The presence of thick clouds (e.g. cumulus/cumulonimbus and nimbostratus clouds) and other high water content clouds, which could vary from months to months may account for variation of most solar parameters studied in this work.