This paper describes field experiments and numerical simulations on hybrid utilization of renewableenergy and polymer electrolyte fuel cells for a residential energy system. It presents the results ofempirical testing and evaluation of hybrid utilization involving solar energy. First, field experiments wereconducted on an electric power and domestic hot water supply system that uses both solar energy andfuel cells on sunny days in Sapporo. The system achieved a 46.6% reduction in primary energyconsumption compared with conventional systems. Secondly, a simulation was performed on theoptimum scale and effect of introduction of the system. The simulation shows that the optimum capacityof the polycrystalline silicon photovoltaic cell and polymer electrolyte fuel cell to minimize primaryenergy consumption in Sapporo was 27 m2 (max. output: 2.8 kW) and 1.1 kW, respectively, under thecondition where reverse power flow was not taken in account. The hybrid system of electric power anddomestic hot water supply was analyzed for residential energy systems in Sapporo and Tokyo. It wasalso clarified that when heat from the hybrid system with a solar collector was used only for domestichot water supply, the optimum capacity of the fuel cell was approximately 1 kW in Sapporo.