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Last week General Motors (GM) unveiled a hydrogen-fuel-cell-powered version of its Chevrolet Volt concept, a family of electric cars that get a portion of their energy from being plugged into the electrical grid. The first version, announced in January, married plug-in electric drive to a gasoline or ethanol generator that can recharge the battery.

But swapping out the generator for a fuel cell may be a step backward. That is in part because producing the hydrogen needed to power the fuel-cell version could increase rather than decrease energy demand, and it may not make sense economically.

“The possibility that this vehicle would be built successfully as a commercial vehicle seems to me rather unlikely,” says Joseph Romm, who managed energy-efficiency programs at the Department of Energy during the Clinton administration. “If you’re going to the trouble of building a plug-in and therefore have an electric drive train and a battery capable of storing a charge, then you could have a cheap gasoline engine along with you, or an expensive fuel cell.” Consumers will likely opt for the cheaper version, Romm notes.

Still, the Volt is part of a promising trend toward automotive electrification–which could decrease petroleum use and reduce carbon emissions. It is part of GM’s response to an anticipated future in which both petroleum and carbon-dioxide emissions will carry a heavy price, driving consumers to buy vehicles that run on alternative, low-carbon power sources.

The new Volt, announced in Shanghai, replaces the generator with a fuel cell and cuts the battery pack in half, in part to make room for storing hydrogen. The lithium-ion battery pack can be recharged by plugging it in. The fuel cell kicks in immediately when the car is started and provides power at a constant rate at which it is most efficient. If more power is needed, such as for acceleration or high speeds, the battery provides a boost of power, much like what happens in today’s gas-electric hybrid vehicles. When less power is needed, such as when the vehicle is stopped or at low speeds, the battery stores energy to be used later.

By allowing the fuel cell to run at a constant rate, the batteries improve efficiency, cutting down on hydrogen consumption. The battery further improves efficiency by storing energy generated during braking. Compared with earlier prototypes, the new concept also uses a more advanced fuel-cell design (thinner stainless-steel parts were substituted for thick composite parts) and the vehicle is lighter, making it possible to have a 300-mile range using half the hydrogen.

The car emits no harmful emissions from the tailpipe. But because hydrogen fuel today is primarily made from fossil fuels this means the carbon-dioxide emissions are simply happening someplace else, Romm notes. He says that using renewable energy to charge up the battery in the gas-generator version of the Volt makes more sense than using it to make hydrogen. That’s because it’s more efficient to charge a battery than to make hydrogen, compress it, and then convert it back into electricity using a fuel cell.

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Credit: GM

Tagged: Energy, batteries, electric cars, electric vehicle, ethanol, flexible electronics, automobiles, fuel cells

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