We describe a model adopted for tropical regions showing the dependence of surface solar radiation reaching the ground level, on atmospheric constituents. The spectral solar shortwave irradiance is calculated from spectral transmittance in a cloudless tropical atmosphere, based on Rayleigh scattering and aerosol extinction factors parameterized according to conditions characteristics of African Great Lakes region. A Monte Carlo simulation is used to calculate the transmittance and reflectance of a homogeneous atmosphere based on Rwanda, which in turn determines the solar radiation reaching the ground level. The results show that this simple model is sufficient for deriving realistic representations of the incident solar radiation on Earth’s surface for a range of atmospheric turbidity values.