A model for calculating direct and diffuse solar radiation

A new model is presented for computing both direct and diffuse solar radiation for a cloudy sky, based on the model of King and Buckius for the direct component for a clear sky. The model is employed to calculate the daily global insolation incident on a horizontal surface at Ibadan for the year 1977. The results are presented in the form of both weekly and monthly averages, and compared with the experimental data provided by the International Institute of Tropical Agriculture (I.I.T.A.), Ibadan. Two values of cloudiness coefficient k (= 1.0 and 0.75) are used in the calculations, with the case of k = 0.75 being superior and for which the deviations from the data do not exceed 15 per cent.