Estimation of Diffuse Fraction, Hourly and Daily Clearness Indices over Kano and Port-Harcourt Nigeria using NCEP/NCAR Satellite Data

Estimation of Clearness index and Diffuse fraction were calculated using available satellite data obtained from National Centre for Environmental Prediction (NCEP) and National Centre for Atmospheric Research (NCAR) data base covering a period of 10 Years. Direct solar data and diffuse solar data collected were added to give the Global solar radiation. The clearness index (K_T) which is the ratio of the global solar radiation obtained at the surface to the total solar radiation at the top of the atmosphere was obtained. The diffuse fraction (K_D) was obtained from the ratio of the diffuse solar radiation incident on the horizontal level of earth surface (H_D) to the global solar radiation that incident on the surface level (H).The computed clearness index value were used to characterize the sky conditions into clear skies and overcast skies. Port-Harcourt with low clearness index indicated low global solar radiation while Kano with large clearness index indicated high global solar radiation. The implications of these results on the effective utilization of solar energy are discussed. The results also serve as very useful for solar energy collectors in designing and estimation of solar application systems.