A numerical forecasting model of the on-site solar spectral irradiation for photovoltaic generation is developed by coupling a meteorological model and an atmospheric irradiance model. The intensity of the solar irradiance, which mainly changes due to clouds shading and scattering, is one of the dominant parameters of the photovoltaic power generation. The coupled model developed in this study consists of three parts: First, the mesoscale meteorological model is applied to evaluate the atmospheric condition including clouds existance. Next, the optical thickness of clouds is evaluated by considering the amount of clouds and diameter distribution of their particles. Finally, the direct and scattering solar irradiance at the ground is evaluated by taking into account not only the effect of the clouds but also the atmospheric gasses, e.g. Ozone, Oxygen and Carbon Oxide, in each wave length. The direct and scattering solar spectral irradiance evaluated with this coupled model is applied to compute the electric generation of any kind of photovoltaic systems. The coupled model's forecasting can be applied to control the unstable photovoltaic output from the ordinal power generators.
