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March 2, 2006

Fuel Cell/Battery Hybrid Fork Lifts

Hybrid vehicles operating in an unusual environment are lifting the prospects of fuel cells.

Source: Technology Review

The future of fuel-cell vehicles is already happening in an unlikely proving ground: forklifts used in warehouses. Several manufacturers are testing forklifts powered by a combination of fuel cells and batteries -- and finding that these hybrids perform far better than the lead-acid battery systems now typically used. In some situations, in fact, they could pay for themselves in cost savings and added productivity within two or three years.

The adoption of the technology points to a promising hybrid strategy for finally making fuel cells economically practical for all sorts of vehicles. While researchers have speculated for years that hydrogen fuel cells could power clean, electric vehicles, cutting emissions and decreasing our dependence on oil, manufacturing fuel cells big enough to power a car is prohibitively expensive -- one of the main reasons they are not yet in widespread use. But by relying on batteries or ultracapacitors to deliver peak power loads, such as for acceleration, fuel cells can be sized as much as four times smaller, slashing manufacturing costs and helping to bring fuel cell-powered vehicles to market.

The forklift hybrids use ultracapacitors, devices similar to batteries but able to deliver higher bursts of power. The fuel cell powers the forklift as it drives through a warehouse, while at the same time the cell charges the ultracapacitors. The ultracapacitors kick in to lift a pallet.

"If you had to do that with just fuel-cell power, you'd need a fuel cell about four times as large, which would be too big," says Michael Sund, spokesperson for Maxwell Technologies, an ultracapacitor manufacturer. "It would dwarf the forklift, and it would also be very expensive. Being able to downsize the fuel cell makes it smaller, lighter, and cheaper."

The use of the fuel-cell hybrids in forklifts could bode well for the auto industry. Cars and SUVs, like forklifts, have peak power demands. When cruising, they use less than one-quarter of an engine's maximum power, which is sized to provide acceleration and sustained power up long hills, says Brian Wicke, who's developing fuel-cell systems at GM.

Batteries and ultracapacitors could provide at least some of the accelerating power, allowing the fuel cell to be smaller. Last year, GM rolled out a concept car featuring a hybrid system, although it will be after the end of the decade before such a vehicle is available. Other major automakers are also pursuing the hybrid technology.

In addition to supplying peak power, ultracapacitors and batteries give fuel-cell vehicles the ability to recapture energy from braking, as happens now with commercial gasoline-battery hybrid vehicles. This can make the system much more efficient, especially in applications such as city driving. A vehicle powered by a fuel cell alone would not have this ability.

"You can't take energy into a fuel cell. You've got to have a battery," says Brian Barnett at Tiax in Cambridge, MA, a company that has provided analyses of fuel cells for the U.S. Department of Energy. "Why you would put an electric drive train system on the road, and not have the ability to accept regenerative braking is beyond me."

Exactly how much batteries could lower the cost of fuel cell-powered cars and SUVs would vary as car makers balanced the different strengths of fuel cells and batteries. Batteries and ultracapacitors can provide power at less cost than a fuel cell, but they run out of energy quickly. The strength of fuel cells is that they can keep running as long as they have hydrogen, and can be refueled faster than a battery can be recharged.

In the future, the mix of batteries and fuel cells could be optimized for different kinds of vehicles, says GM's Wicke. "There is a very broad mix of possibilities, starting with a fuel-cell vehicle which is augmented by a battery, all the way to a battery vehicle augmented by a fuel cell -- and you could have almost any mix in between," he says. GM is currently focused on the first approach, using a battery to boost the performance of a still relatively large fuel cell, while improving efficiency by capturing energy from braking.

While hybrid systems could help make fuel-cell vehicles more affordable, other obstacles need to be overcome before these vehicles take over the roads. Fuel cells can run only as long as hydrogen is available, and that will require better ways of storing hydrogen in the vehicle and distributing it. One of the reasons forklifts are a first application of hybrid fuel cells is that they never move far from their filling station.