This research aims to minimize the cost of the PV system according to minimization of the PV array area and storage battery. In this paper, a new method is used to calculate the minimum number of storage days and the minimum PV array area. The pre-operating time of the diesel-generator is also incorporated in our system design. A system sizing program using FORTRAN language is developed. The program is used to size our experimental system which consists of a PV system, storage subsystem and diesel-generator. The proposed sizing program can be used to size any system. A comparison between stand-alone and hybrid system sizing is presented in this paper.