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Ultracapacitors: Maybe Not Miracle Workers, but Great EV Power Potential

Everybody talks about batteries for electric cars, but much less is said about ultracapacitors, a related form of storage that has the advantage of discharging large doses of high-voltage electricity. The drawback is that they're not very good at holding on to energy--it's a process of quick release.

Most analysts don't think that ultracapacitors will single-handedly power car-based EVs anytime soon, but there's a wild card in the mix: A secretive Texas-based company called EEStor, which claims to be able to work miracles with ultracapacitors.

EESTor, which says its ultracapacitors can give a car 300-mile range, has some true believers. Although EEStor isn't publicly traded, partner Zenn Motor Company (which owns almost 11 percent of EEStor) is. And according to an account in Wired by EV insider Darryl Siry, Zenn stock climbed more than 100 percent after EEStor announced a breakthrough last April. Siry said that EEStor could be worth $1.5 billion (on paper anyway). Zenn has really had a heavy dose of the EEStor Kool-Aid: It abandoned the EV business entirely to serve as a marketer of the Texas company's technology. And the strategy seems to be working, since Zenn promptly raised nearly $10 million (Canadian) on the strength of ultracapacitors nobody's seen in action--and many analysts think are technically impossible.

David Schramm, CEO of San Diego-based Maxwell Technologies, is being much more cautious. He doesn't claim his ultracaps can give a car 300-mile range, and he's clearly skeptical about EEStor's claims. Maxwell caps are in the pitch control systems of German wind turbines (to help them turn when the wind changes), and help provide juice to mission-critical uninterruptible power sources (UPS) at data centers and telecoms.

The Global Ultracapacitor Market Analysis and Forecasts to 2015 sees more than 25 percent annual growth for the ultracapacitor market in the next six years. They have a big role to play in the smart grid, which is benefiting from billions in federal aid.

"Our strategy is to keep our heads down and execute," Schramm said, "You have to put what you have on the table." In Maxwell's case this means ultracapacitors installed in up to 1,000 hybrid transit buses. The idea is not to power the whole bus, but to store regenerative braking energy, and release power to aid in acceleration. Maxwell claims a 50 percent increase in fuel consumption and a 90 percent particulate emission reduction in equipped buses.

Maxwell ultracaps aren't in cars yet, but Schramm said he has just concluded an agreement with the $37 billion Continental AG to become part of the stop-start system in a range of forthcoming European hybrid vehicles from Tier One automakers. "We're specced into those systems, and we've been told to expect a 10-fold increase in orders by 2011," Schramm said.

Schramm said that some customers have powered buses solely with ultracapacitors, but these make short runs of 1.8 miles and recharge at bus stops. Ultracaps, he said, charge and discharge electricity quickly, and (unlike some batteries) work at both very high and low temperatures. "When you try to start your car in the winter, that's a battery not wanting to work in the cold," Schramm said.

Maxwell has partnered with Argonne National Laboratories on work getting batteries and ultracaps to play nicely together. According to MIT's Technology Review, Argonne researchers think ultracaps can lower the cost of plug-in hybrid battery packs "by hundreds or even thousands of dollars." The key: Ultracaps, strategically deployed, reduce the need to oversize battery packs. A 25 percent size reduction saves about $2,500. And ultracapacitors significantly reduce heat stress on battery systems.

Another use for ultracapacitors is in very small "microhybrids," according to the Institute of Transportation Studes at the University of California, Davis. These cars would use batteries and electric motors with an ultracap for start-stop systems and regenerative braking.

The remaining hurdle with ultracapacitors is reducing their cost to about half what they are now. No doubt EEstor has that one licked.