RESUMO
In this work, a physical model based on the radiative transfer equation is presented to estimate the global solar irradiance on top of the Earth's atmosphere surface. A link is established among the radiative transfer through the atmosphere, the geographic coordinates of a city (longitude, latitude), time of day, and date of the year. The discrete spherical harmonics method is applied to solve the radiative transfer equation. The city of Dschang in Cameroon is taken as an example of application of the model. This city is located at latitude 5°44'N and longitude 10°04'E. It is assumed that the atmosphere of the city is inhomogeneous and composed of non-polarizing Haze L aerosol particles in gamma distribution, while the ground surface diffuses radiation isotropically. The predictions are compared under clear sky conditions to some existing models of irradiance such as the Bird model and Davies and Hay model for a homogeneous atmosphere. Results demonstrate that the present investigation matches well with the Bird and the Davies and Hay models and is valuable for ground solar irradiance estimation. The effects of the inhomogeneity of the atmosphere on total insolation are also studied, and our results indicate that the inhomogeneity of the atmosphere reduces local insolation. The present study shows that the radiative transfer model is an efficient technique for estimating global solar radiation at any level of the stratified atmosphere and under different atmospheric conditions.
