In your Jan. 19 issue, Thomas Wyman argues that, because “it simply takes more energy to extract hydrogen from water using electrolysis or to extract it from methane using steam reformation than can be obtained from the subsequent use of the extract hydrogen as a fuel…the pursuit of the hydrogen economy brings to mind the age-old search for the perpetual motion machine” (OGJ, Jan. 19, 2009, p. 14).
Mr. Wyman is ignoring the remainder of the fuel cycle. Obtaining hydrogen from natural gas is 65-75% efficient, so we start by throwing away 25-35% of the energy in the natural gas. For use as a vehicle fuel, both natural gas and hydrogen must be transported and compressed into a high pressure storage tank onboard the vehicle; hydrogen probably will end up the loser here, too, because its low energy density demands a higher storage pressure than natural gas for equal range.
However, the saving grace is hydrogen’s end use efficiency onboard the vehicle. The efficiency of a dedicated natural gas vehicle, accounting for both the weight of the storage tanks and the efficiency boost from methane’s high octane, is likely to be only slightly better than that of a gasoline vehicle with similar technology. And right here is hydrogen’s theoretical potential. If the efficiency of a practical fuel cell system can reach the levels hoped for, it will be more than twice as efficient as an internal-combusion-engine (ICE)-based power train—with zero tailpipe emissions.
Although these results are a bit dated, let me compare total fuel cycle energy use for dedicated natural gas vehicles vs. hydrogen (from natural gas) fuel cell vehicles from the “1.5” version of Argonne National Lab’s GREET (fuel cycle) model: The natural gas vehicle uses about 3% more energy than a similar gasoline vehicle; the hydrogen fuel cell vehicle uses 50-60% less energy than a similar gasoline vehicle.
I’d be the first to admit that these values, especially the fuel cell values, are based on assumptions about R&D success. Also, I believe that future improvements in ICE engines and transmissions will make the energy comparison somewhat less favorable to fuel cells. And there are enormous cost and infrastructure development hurdles to be overcome before hydrogen fuel cell vehicles can compete well with gasoline vehicles.
Nevertheless, a hydrogen economy is no perpetual motion machine; it is an option, one of several, worth pursuing in any drive to reduce US dependence on oil.
Steve Plotkin
Rockville, Md.
