Wind-photovoltaic hybrid system (WPHS) utilization is becoming popular due to increasing energy costs and decreasing prices of turbines and photovoltaic (PV) panels. However, prior to construction of a renewable generation station, it is necessary to determine the optimum number of PV panels and wind turbines for minimal cost during continuity of generated energy to meet the desired consumption. In fact, the traditional sizing procedures find optimum number of the PV modules and wind turbines subject to minimum cost. However, the optimum battery capacity is either not taken into account, or it is found by a full search between all probable solution spaces which requires extensive computation. In this study, a novel description of the production/consumption phenomenon is proposed, and a new sizing procedure is developed. Using this procedure, optimum battery capacity, together with optimum number of PV modules and wind turbines subject to minimum cost can be obtained with good accuracy.