The Dark Horse in the Race to Power Hybrid Cars By Larry Greenemeier Scientific American
MEAN GREEN MACHINE: An ultracapacitor-equipped Toyota Supra HV-R coupe was the only hybrid to win the 24-hour endurance race held at Japan's Tokachi International Speedway. Courtesy of Toyota Motor Sales, U.S.A., Inc.
The greatest victory so far for the cars, fueled by a combo of electricity and gas, came just weeks ago when an ultracapacitor-equipped Toyota Supra HV-R coupe became the first hybrid to win the 24-hour endurance car race held at Japan's Tokachi International Speedway. The hybrid Supra finished 616 laps of the 5.1-kilometer (roughly threemile) course—19 more laps than the second-place nonhybrid Nissan Fairlady Z. "The Toyota that won was able to deliver energy more quickly, accelerate faster, and use braking generation more efficiently," says Kevin Mak, an analyst with research and consulting firm Strategy Analytics and author of a recent study that explores the potential for ultracapacitors to complement and possibly even replace batteries in hybrid vehicles. "The days of the large hybrid vehicle battery pack may be numbered," he adds.
The reason, he says: capacitor technology that stores energy in the electric field between a pair of closely spaced conductors. An ultracapacitor, also called a supercapacitor, is an electrochemical capacitor with a higher energy density than normal capacitors, which potentially makes them a better fit for hybrid vehicles.
Ultracapacitors store electricity by physically separating positive and negative charges. Batteries store energy using toxic chemicals and their effectiveness fades over time. In addition, recycling the heavy metals in batteries is a difficult task. Capacitors, on the other hand, are constructed of much smaller fine carbon nanotubes, Mak says.
A major advantage of ultracapacitors is their ability to efficiently capture electricity from regenerative braking systems and provide that electricity to power a car's acceleration. Ultracapacitors not only charge more quickly than batteries, they also release energy more quickly, Mak says.
A drawback to their use is the technology's inability to store as much energy as a battery. But the Tokachi race proved that ultracapacitors could be more widely used in conjunction with smaller batteries to power hybrid cars. "Without the need for chemicals, capacitors can be lighter, thereby enabling the hybrid car maker to improve fuel economy further and reduce costs," Mak says. "The low weight would then make hybrid power trains more readily available to compact car segments as [has been] seen on Honda and Mazda concept cars since 1997."
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