Regenerative fuel cells for energy storage: efficiency and weight trade-offs

In optimizing regenerative fuel cell systems for a given application, the operating efficiency of both the fuel cell and electrolyzer may be traded against the stack mass. Both efficiency and mass are important characteristics for energy storage, particularly for aerospace applications. This paper reports the results of a trade-off study conducted to optimize the design of regenerative fuel cell systems used in conjunction with a PV array. The results suggest that high efficiency does not necessarily provide the highest specific energy, and that the highest specific energy of the energy storage subsystem does not result in the lowest mass of the entire power system. Optimum cell voltage (in both fuel cell and eleetrolyzer modes) strongly depends on the duty cycle of the system, i.e., duration of chargingldlscharging and capacity factor in charging and discharging, as well as the fuel cell I electrolyzer polarization curves and hydrogedoxygen storage characteristics. the advanced battery systems. These regenerative fuel cell systems may be used in applications where relatively large amounts of energy must he stored. These applications include energy storage for remote off-grid power sources, emergency or back-up power generation, zero emission vehicles, hybrid energy storagdpropulsion systems for spacecraft, and high