ELECTRICAL POWER SYSTEM

PROBLEM TO BE SOLVED: To provide an electrical power system which keeps the state of a storage battery suitably by saving fuel without annexing a converter for charge/discharge control to the storage battery in an electrical power system where a fuel cell and a storage battery are combined.SOLUTION: This electrical power system supplies a load with power by connecting an accumulator and a fuel cell device each in parallel with the load. The accumulator is equipped with a secondary battery pack where one piece or plural pieces of secondary batteries are connected in series or in parallel. The fuel cell device is equipped with a fuel cells stack where a plurality of fuel battery cells are stacked, a DC/DC converter which converts power generated by the fuel cell stack and supplies it to the output of the fuel cell device, a voltage detector which detects the output voltage of the fuel cell device, a current detector which detects the output current of the fuel cell device, and an accumulator state determiner which determines the charge/discharge state of the accumulator from an output voltage value detected with the voltage detector and an output current value detected with the current detector and controls the output voltage of the DC/DC converter based on the determination results.