Estimation of Global Solar Radiation in Onitsha and Calabar Using Empirical Models

Author(s): M. N. Nnabuchi, J. E. Ekpe, G. F Ibeh

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Understanding solar radiation data is essential for modelling solar energy systems. The purpose of the present study was to estimate global solar radiation on horizontal surface using meteorological parameters for a period of eleven years (1996 "“ 2006). Monthly average global solar radiation, H has been estimated for Onitsha and Calabar, Nigeria using predicting models generated by simple linear and multiple regression analyses. The models included a one variable model with relative humidity as the independent variable and two three-variable models correlating H with relative humidity and each of average temperature, cloudiness index and number of sunshine hours. The values of the global solar radiation estimated by the models and the measured solar radiation were tested using the mean bias error (MBE), root mean square error (RMSE) and mean percentage error (MPE) statiscal techniques. The values of the correlation coefficient (CC) were also determined for each model. The model that indicate a good agreement between the measured and estimated values for Onitsha and Calabar are  and  respectively. The developed models can be used for estimating global solar radiation in Onitsha and Calabar and other locations with similar climatic factors.