a fuel cell power generation system in which the temperature of fuel cells is held constant irrespective of the load level of the cells , and waste energy is effectively recovered , that is , heat generated by fuel cells or a hydrogen producing device is temporarily stored , thereby to absorb the fluctuations of generated heat attendant upon the load fluctuation of the fuel cells and also to generate steam required in the hydrogen producing device by the use of the stored heat . when the heat generated by the cells is little as in a low load operation or a stand - by state , the stored heat is used for heating so as to allow power to be generated immediately upon a load demand .