Because the fuel cells are more efficient at part load than at rated power, the case for hybridizing a fuel cell vehicle is different. One motivation for hybridizing the FC vehicle is to improve its fuel economy by recovering a portion of the braking energy.Hybridization can also help if the energy storage device has higher specific power (kW kg−1) and lower cost ($kW−1) than the FCS. Because of higher part-load efficiency, even in a hybrid configuration it appears advantageous to operate the FCS in a load-following mode and to use the power from the ESS when the FCS alone cannot meet the power demand. For hybrid vehicles, the fuel cell systems may couple best with high power, lowenergy storage devices such as supercapacitators.