Statistical study of variation of diffuse solar radiation over Nigeria

Abstract

Multiple regression models have been developed to study the variation of diffuse solar radiation over Nigeria using monthly mean data of clearness index, relative sunshine duration, average temperature and cloud cover. The data for eight stations representing the weather conditions of Nigeria and covering a period 16 years were analyzed, and the statistical accuracy of the regression equations were evaluated by root mean square error, stand-ard error, mean bias error, t-statistic, correlation coefficient and coefficient of determination. The regression prod-uced good correlation between the dependent variable of fraction of diffuse solar radiation and the independent variables of clearness index, relative sunshine duration, cloud cover and average temperature. The multiple regre-ssion equations reflected the spatial variability with the latitudes, and can be used for prediction of diffuse solar radiation in Nigeria. A temporal and spatial diffuse solar radiation contour map was developed using Surfer 10 Golden graphic software.

Keywords: Multiple regression, Diffuse solar radiation, Clearness index, Cloud cover, Correlation coefficient