The hype surrounding Toyota Motor's recent announcement that it will begin selling a car powered by hydrogen fuel cells in the US next year obscures an inconvenient truth. The energy needed for the production of hydrogen guarantees that a car powered by fuel cells will be less efficient than a comparable car powered by natural gas.
There are basically two ways to make hydrogen: electrolysis of water and steam reforming of natural gas. Essentially all of the hydrogen produced in the US today is made by the latter process. This is a very well-known industrial process since it is the first step in the production of nitrogen fertilizer.
A large fertilizer producer uses 4.3 kg of natural gas to make 1.0 kg of hydrogen. The fuel cell yields 17.4 kw-hr of electrical energy from the 1.0 kg of hydrogen (after allowing for the energy used in compressing the hydrogen). Toyota has not yet released fuel consumption or electrical energy consumption data for its fuel cell car, the Mirai, but it is possible to make some estimates.
The Tesla Model S plug-in electric vehicle uses 0.32 kw-hr/mile, so it will travel 54.4 miles on 17.4 kw-hr of electrical energy. The Tesla, of course, has regenerative braking and a curb weight of 4,640 lb. The Mirai also has regenerative braking and a curb weight of 4,080 lb. Let's suppose the Mirai also uses 0.32 kw-hr/mile. Then it will also travel 54.4 miles on 17.4 kw-hr of electrical energy derived from 1 kg of hydrogen. Production of this kilogram of hydrogen from natural gas by the steam reforming process requires 231 cu ft of natural gas.
Now suppose that instead of making hydrogen we simply equipped the Mirai with an internal combustion engine and burned the natural gas. The vehicle we would have is similar to the Lexus GS 450h hybrid, which has a curb weight of 4,190 lb and an EPA fuel economy rating of 34 mpg (highway). We would need only 191 cu ft of natural gas to power this car for 54.4 miles. So using natural gas to produce hydrogen which is then used to power a fuel cell car requires 1.2 times the amount of natural gas required by burning the natural gas directly in an internal combustion engine-and we don't need a $57,000 vehicle to do it.
The proponents of fuel cell cars would like us to believe that the only impediment to their grand "hydrogen economy" is a dearth of refueling stations, when the real problem is the second law of thermodynamics. We need to stop subsidizing fuel cell cars with tax credits and access to car pool lanes.
Donald F. Anthrop
Berkeley, Calif.
