In this paper a hybrid generation system for a practical stand-alone application in Iran is proposed. This study considers Wind-Turbine Generators (WTG), Photovoltaic (PV) systems, battery banks and diesel generator as power sources. The investment costs and fuel cost are minimized while ensuring the availability of the energy needed by customers. The presented generation scheme should be able to produce sufficient power to cover the peak load. PV and WTG as well as battery banks are utilized as primary power sources and a diesel generator as a backup power for the system. The stand-alone system is designed based on the local data of solar radiation and wind speed along with operation states for system load in 24 hours. The Particle Swarm Optimization (PSO) is used to obtain the optimal sizes for WTG, PV, battery banks and the diesel generator.