The methodology for optimally sizing the combination of battery banks, photovoltaic (PV) arrays, and wind turbines is presented in this article. With regarding the economic cost, system capacity, and power supply reliability as constraint conditions, the proposed method is applied to get the most economical configuration in condition of attaining the system's power supply requirement. A case study to design a photovoltaic/wind hybrid system by using the meteorological data of Beijing is set as an example for illustrating the methodology by using long-term data of wind speed and solar irradiance recorded every month for the past 30 years. The data were used to calculate the average power generated by a wind turbine and a PV array. For a given load and a system capacity, optimum numbers of battery banks, PV arrays, and wind turbines were calculated to get the minimum cost of the system configuration.