Estimation of Global Solar Radiation and Clearness Index in Coast of Gulf of Guinea, Nigeria

Document Type : Original Article


1 Department of Physics and Solar Energy, Faculty of Science, Bowen University, Iwo, Nigeria

2 Department of Computer Science and Information Technology, Bowen University, Iwo, Nigeria


The concept of solar energy and its applications in present day would come to be one of the solutions to our Nigerian problem of instability and epileptic power supply. In this study, data for mean monthly sunshine hours  and global solar radiation  for Ikeja, Lagos state capital (6.580N, 3.320E) were obtained from Nigeria Metrological Agency (NiMeT), Oshodi Lagos, Nigeria and spanned 1996 to 2010. The data for global solar radiation were measured using a Gunn-Bellani radiometer. A linear regression correlation model was developed for Ikeja and other surrounding area in south-western part of Nigeria with similar meteorological conditions. The results of estimated global solar radiation ranged from 5.1 MJm-2 day-1 on average for August and 13.1 MJm-2 day-1 for March for Lagos. The Angstrom constants a and b of Angstrom-type correlation to estimate monthly average global solar radiation was estimated to be 0.25 and 0.63 respectively. The result for global solar radiation were then subjected to statistical tests [MBE, RMSE, MPE] and proved to be good estimates. The value of clearness index was also estimated to range from 0.31 to 0.59 showing Lagos as a partly clear sky city.