Today, there are roughly 750,000 plug-in electric vehicles on U.S. roads and about 3,800 powered by hydrogen fuel cells.
Proponents of each type of vehicle argue strenuously that their powertrain is a better way to produce vehicles with zero emissions from the tailpipe.
Electric cars can be charged at home overnight, and electricity in many areas is far cheaper than gasoline on a per-mile basis, say the plug-in vehicle supporters.
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Ah, but hydrogen vehicles have far longer ranges, need to be fueled less often, and employ the familiar model of visiting a fueling station that drivers are already used to, counter the hydrogen proponents.
It's far too early to know how this battle will play out. Some analysts suggest electricity may be the preferred mode for smaller passenger vehicles, while hydrogen is better suited to such large vehicles as semi tractors, perhaps even full-size SUVs.
But there's one metric in which it's very hard for hydrogen to come out ahead: energy use.
Energy requirements for vehicle powered by hydrogen (L) vs electricity (R) [image: Ulf Bossel]
A single chart, published in a December 2006 article on Phys.org shows the added steps required to process hydrogen and turn it back onto electricity to drive the electric motor that powers a hydrogen fuel-cell vehicle's wheels.
If you start with the same kilowatt-hour, whatever the source (from coal-powered to entirely renewable), using that energy to make hydrogen produces fewer miles on the road than it does when used to charge an electric car.
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That translates to a lower carbon footprint per mile for the electric car against the hydrogen one.
The numbers only come out evenly when all energy is renewable, at which point the carbon footprints are so negligible that any minor differences in manufacturing and transport likely don't matter.
2015 Hyundai Tucson Fuel Cell, 2016 Toyota Mirai at hydrogen fueling station, Fountain Valley, CA
Until that point, which even under the most remarkably optimistic scenario will not arrive before 2050—if not 2100—the energy required to drive a mile on hydrogen is higher than that needed to drive a mile in a battery-electric car.
It is possible to create studies that show more favorable results for hydrogen, in part by cherry-picking data to use different grids with different carbon intensities.
But wherever the same kilowatt-hour, from the same source, with the same carbon intensity is used either to charge a battery or to create hydrogen fuel for a vehicle, the electric car wins.
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If the policy goals for zero-emission vehicles are to eliminate tailpipe emissions, then both types of vehicles score equally, since the water vapor from the hydrogen vehicle is harmless.
But if the goal is to radically reduce the emissions of the greenhouse gas carbon dioxide associated with road vehicles, electric cars will always be better unless all hydrogen is produced renewably but most batteries are charged using non-renewable energy.
It's important to note here that hydrogen vehicles generally have a lower carbon footprint than most gasoline cars today—and that California requires renewable sources to be used for at least one third of the energy used to make hydrogen, which today is largely derived form natural gas.