Estimation of Global Solar Radiation in Nigeria using a modified Angstrom Model and The Trend Analysis of the Allied Meteorological Components

This study was carried out to investigate the trend of some common and related atmospheric variable in the light of climate change on annual time scale and to further develop a suitable scheme for the simulation of annual global solar radiation Nigeria. In this connection, annual trends of global solar radiation, air temperature, precipitation, relative humidity and sunshine hours was carried out; covering about 13 tropical stations and fairly representing the different climatic features in Nigeria. Annual trends in the above named atmospheric variables were detected at the 13 stations in 1975-2007 in Nigeria and using F-test as the significance test technique. 9 stations exhibited an upward trend in global solar radiation series of which 6 passed F-test at 1% significant level. At 11 stations, precipitation had shown an increasing trends but none passed-test at 2.5% and hence not significant. About 98.8% of the stations displayed an upward trend in sunshine hours of which 16%passed F-test at 1% significant level. On trend analysis for relative humidity series, 8 stations exhibited a positive trend and having 1 station that passed F-test at 1% at significant level. The trend of temperature series in Nigeria under the period under investigation were found to be increasing at 12 stations and having 8 stations that passed the F-test at 1% significant level. The second objective of this study is to determine a more suitable empirical equation by modifying Angstrom model for the estimation of global solar radiation. This aim was accomplished by using all the data for all the 14 stations pooled together to predict global solar radiation; this is done so as to improve the low performance of the Angstrom model used for the annual estimation of global solar radiation. The model parameters ‘a’ and ‘b’ of Angstrom Model were parameterized in terms of the geographical locations (latitude, longitude and elevation) and the meteorological variables (sunshine hour, precipitation, relative humidity and temperature) respectively and both. This scheme gave a better a simulation of the global solar radiation compared with the other schemes and the original Angstrom models. In addition, the preferential consideration of relative humidity to precipitation as potent contributive factor in the estimation of global solar radiation was also established