Analysis of sky conditions using solar radiation data over a tropical station

Abstract

Radiation data in Nigeria are very sparse because radiation is not routinely measured. The data used for this work are from the physics Department of Obafemi Awolowo University, lle-lfe which is one of the few stations that collect radiation data in Nigeria. The daily, global and diffuse radiation measurements have been used to characterize the atmosphere of lle-lfe (70 14` N, 40 35` E) during January to December 1994. The clearness index ky (=H/H0) which gives the percentage depletion by the sky of the incoming global radiation and the relative sunshine (s/s0) gives the measure of cloud in the atmosphere has been adopted for use in this study. Also investigated are the diffuse radiation Kdiff (=Hdiff/H) and the diffuse coefficient Kcoef (= Hdiff/H0) that mirror the effectiveness of the sky in the scattering of the incoming radiation. Results show an average Kt value of 0.57 for year 1994 with maximum clearness index occurring in June (Kt= 0.68) and minimum in Dec (Kt =0.42). This present study also shows that the relative sunshine s/s0 has its minimum in August which indicates reduced hours of sunshine and solar insolation during the monsoon month of August in the tropical Nigeria station. Keywords: Daily, global and diffuse radiation, clearness index, diffuse coefficient, relative sunshine [Global Jnl Pure & Appl. Sci. Vol.9(3) 2003: 387-392]