This paper presents an Optimization Sizing of a stand-alone PV/FC/Wind Hybrid System (PFWHS) to optimize the sizes of components of PFWHS. Based on PSO algorithm, one optimal sizing method was developed to determine the optimal configuration of system that can achieve the load required power supply probability (Reliability) with a minimum overall cost of energy (OCE).PFWHS costs involve investments, operation and maintenance as well as loss of load costs. The applied wind and radiation datasets belong to northwest region (Jolfa, latitude: 38_56, longitude: 45_37, altitude: 710, m) of Iran. In this paper the impact of availability of PFWHS components is investigated on optimal sizing. So, to investigating the impact of component availability rate on PFWHS costs and reliability due to failure and repair rate of PFWHS components and uncertainty in wind speed and solar irradiance, two scenarios are considered. In first scenario the availability of all components is considered 1 and in second scenario isn’t considered 1 because of failure and repair rate of components and uncertainty in wind speed and solar irradiance. Obtained results prove that while the overall cost of energy is optimized, the reliability indices are within a satisfactory bound with regard to the reliability standards. Also the results indicate that considering complete availability of components causes more reliability rate, so to achieve the actual behavior of PFWHS, the rate of components availability must be considered in suitable insight to designer for supply the load.