This article presents a numerical model which can estimate the energy conversions of separate and hybrid solar wind systems under variable weather. The model integrates the equations associated with the characteristics of photovoltaic generation, wind energy conversion, energy balance, and battery bank, and uses the local database for radiation, wind speed, and ambient temperature. Once the equation associated with the characteristics of load is given, the numerical model can estimate the monthly and yearly powers output of the separate and hybrid solar wind systems provided with different configurations. As a fundamental research, the presentations of daily profiles of solar radiation, wind energy, and ambient temperature are explained in detail, and the combination of the characteristics of wind energy conversion and battery bank is determined. The condition of hybrid action is shown, and the solutions are certain to be found. The operation strategies of separate and hybrid systems are also presented. (c) 2012 Elsevier Ltd. All rights reserved.