Hybridization: Cost and Efficiency Comparisons for PEM Fuel Cell Vehicles

This paper primarily compares costs and fuel economies of load following direct-hydrogen fuel cell vehicles with battery hybrid variations of the same vehicle. Additional information is included regarding load-following indirect methanol fuel cell vehicles. The key points addressed are as follows: the tradeoff between fuel cell system efficiency and regenerative braking ability; transient effects; and component cost differences. The difference in energy use and costs can vary significantly depending on the assumptions and the hybrid configurations. The mass of the battery pack creates the largest impact in energy use, while system efficiency losses roughly balance out with regenerative braking. For the direct-hydrogen fuel cell system, transient effects are small. These effects are expected to be significant for steam reformer/indirect-methanol systems (analyzed only graphically herein). Cost values are very sensitive to uncertainties, but tend to show similar results to those for energy use: vehicles with larger battery packs and smaller fuel cell systems tend to cost more. A key variable is battery replacement over the life of the vehicle. More frequent replacement required for certain battery technologies evens out the cost differential in comparison to the more expensive but longer lasting battery choices for the hybrids.