An attempt has been made to use a polynomial fitting to model global solar radiation on a horizontal surface that was observed by using Pyranometer at University of Ghana Legon, (U.G), situated in Accra, Ghana. The observed solar radiation data was filtered by using fitting and smoothing methods. The polynomial data fitting method was tested by using different degrees of polynomial curve fittings. The root mean square error (RMSE) was used to calculate the error and the R2 (coefficient of determination) value was also determined. The polynomial fittings were carried out for various periods (pre- harmattan, early harmattan and late harmattan period) of the year.