Solar energy is very attractive because it is non-polluting, nonreplicable, reliable, and pollution free. Four-years intervals measured average daily global solar radiation data on horizontal surfaces at Baghdad and Mosul cities in Iraq were used for the model assessment. Statistical results showed that all four suggested models can accurately predict the solar irradiance on a horizontal oriented surface, indicating the good predictive ability for modeling a horizontal surface. The obtained models have a high value of regression coefficient and give best fit through the measured values. This paper illustrates also the use of mathematical formula to develop a predictive model for the duration of sunshine using measured solar radiation data for above cities. The present work showed that the predicted results were in good agreement with the tabulated data, and the expected solar radiation behavior. Keywords: Global solar radiation, Beam radiation, Diffuse radiation, and relative sunshine duration, clearness ratio dat
