Renewable energy power generation systems are promising energy sources where hybrid solutions such as Photo Voltaic-Wind Turbine (PV/WT) grid connected power systems are largely adopted for their good potentials. Design of such systems requires that particular attention must be paid to an optimal combination between the two different power sources because of the complex nature of several affecting variables. This paper presents an optimal sizing procedure exploiting a Multi Criteria Decision Analysis (MCDA). The proposed approach is described in details and applied to a real scenario.