Aside from those who'd prefer everything to run on profit-rich coal and oil until the skies turn black, the hottest debate on the future of automobiles today involves energy efficiency. Battery-electric and fuel-cell vehicles use competing technologies that share many of the same parts in common, but are intended to fill two very different niches in the marketplace of the future. Of course, that assumes either one will end up filling any niche -- which, in itself, is a pretty explosive subject.
In terms of basic motivation, battery-electric and fuel-cell cars are essentially tthe same. A battery-electric vehicle -- aka BEV or "pure electric" -- is one of the simplest vehicles on the road. It stores electrical energy in onboard rechargeable chemical batteries, and then sends that power to an electric motor when called upon to move the vehicle. The car's electric motor also acts as a generator under deceleration, partially regenerating energy to recharge the batteries. A fuel-cell vehicle is an electric car with a hydrogen fuel-cell that acts as an onboard generator to constantly recharge a much smaller battery pack. In this sense, the hydrogen-fuel-cell car is just like any other series hybrid, which uses a gas or diesel generator to recharge the batteries. But the nature of the cell and fuel changes the equation completely.
A hydrogen fuel cell works by "backward electrolysis." The oxygen and hydrogen atoms on a water molecule are held together by electricity; if you pass enough electricity through the water, it will split the hydrogen-oxygen bonds apart, creating a gas that is two parts hydrogen and one part oxygen. This process produces significant heat as a byproduct; in fact, even a fairly efficient electrolysis plant will waste about 35 percent of its energy creating waste heat during electrolysis. Thermal reclamation can drop that to 20 percent or so, but a certain amount will always go to waste. This holds true when you put the oxygen and hydrogen atoms back together in a fuel cell, reversing the process of electrolysis and creating electricity. A fuel cell, which doesn't use any kind of energy reclamation, almost always wastes 30 to 35 percent of its energy input creating waste heat.
Of course, the biggest problem with any battery-electric vehicle is the range limitation -- not just in terms of the range of a fully charged battery, but in the time needed to recharge it. These two problems become even more pronounced as you start adding range, since adding batteries adds weight, and at some point the batteries will spend more power moving themselves around than moving the vehicle. Currently, lithium-ion batteries are the lightest available; enough so that, for all intents, you'll never wind up carrying so many batteries that you won't gain in range with the addition of more. But these batteries are very expensive, which makes them cost-prohibitive for sales-volume vehicles. A fuel cell is comparatively very light, and its range is effectively infinite because you can top it back up with hydrogen fuel, just as you'd top your car up with gas. Aside from the lack of range limitation, and assuming you have access to hydrogen fuel, a hydrogen-fuel-cell car drives like any electric.
Hydrogen isn't cheap -- not compared to gasoline, and certainly not compared to electricity from your wall outlet. The Spanish Institute Transports Metropolitans de Barcelona found that hydrogen-fuel-cell cars cost a whopping 12 times more to operate than comparable electrics. Even accounting for differences in fuel and electricity costs between the U.S. and Spain, there's an order of magnitude of difference in operating costs between hydrogen and electric vehicles. And that's indicative of a far larger problem with hydrogen cars: namely that it takes electricity to make hydrogen -- which in this case acts as a kind of "liquid battery" -- and you end up losing more than half of that input energy between the hydrogen manufacturing plant and the car. So a hydrogen car will be, at best, 50 percent energy efficient. Compare that to the average battery, which is 95 to 99 percent energy efficient, and there's no contest as to which one is ultimately more efficient. Hydrogen ultimately just shifts your fuel payment from oil companies to coal, gas and nuclear electricity suppliers.
In short: Realistically, hydrogen fuel cells don't have a future in the mass market. They're inefficient energy-wise compared to batteries, which translates to much greater emissions and environmental damage at the point of energy production, and higher operating costs that do nothing but pad the pockets of energy barons. Battery-electrics do have their limitations, but almost anybody can produce endless power with solar arrays on their homes, or retrofit their cars with large thin-film solar cells on the roof that can completely recharge the car's batteries while parked for eight to 10 hours. That means the car ends up running on solar power, instead of ultimately running on nuclear or coal energy like a Victorian-era steamship. But what if you don't have time to recharge your batteries? Tesla already solved that problem, having already engineered battery packs that can be unplugged and replaced by an in-ground mechanism in 30 seconds or less. These racks don't currently exist at service stations, but it's only a matter of time before the Society of Automotive Engineers standardizes pack dimensions and mounting systems, and pack-replacement stations start popping up around the country.
