Capacitors Take The Strain Out Of Charging Hybrid Cars
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Written by Paul M. Gandee
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Tuesday, 14 July 2009 |
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Hybrid cars could become cheaper thanks to a breakthrough that could allow them to run on regular lead acid batteries
HYBRID electric vehicles (HEVs) could become cheaper thanks to a breakthrough that would allow inexpensive lead acid batteries to replace the nickel metal hydride (NiMH) batteries they now use. Similar battery systems could also be used to smooth out fluctuations in the power output of wind turbines.
Lead acid batteries are cheap and can store large amounts of energy. But if they are repeatedly and rapidly charged and discharged as happens when storing braking energy from an HEV and then releasing it when it accelerates the battery's negative plate becomes coated with deposits. That limits its working life to a few years and is one reason why today's HEVs, such as the Toyota Prius, use NiMH batteries.
The UltraBattery developed by Lan Trieu Lam and his team at the Commonwealth Scientific and Industrial Research Organisation in Melbourne, Australia, marries a lead acid battery with a supercapacitor. The combination stores as much energy as a standard lead acid battery, but can happily charge and discharge without deterioration.
Previous experimental systems combining capacitors and batteries have required complicated, expensive electronics to switch between using the capacitor as a short-term store when accelerating or braking, and draining the battery when cruising. Lam's team has instead simply combined battery and capacitor in parallel in one unit. By acting as a buffer during charging and discharging, the capacitor boosts the battery's life to match that of NiMH batteries, Lam says.
In lab tests the UltraBattery lasted four times as long as the best lead acid batteries, while producing 50 per cent more power. The test vehicle the team is running "until the UltraBattery fails" has so far covered 185,000 kilometres while being recharged as needed. What's more, the cost of the battery is a third to a quarter that of NiMH batteries, says Lam, and a sixth that of the lithium-ion batteries used in some high performance electric cars.
Japan's Furukawa Battery Company will start manufacturing the UltraBattery on modified lead acid battery production lines by the middle of next year. In the US, battery manufacturer East Penn in Pennsylvania will make the device.
"It's a clever idea, and it's low cost," says Andrew Burke, a research engineer at the Institute of Transport Studies at the University of California, Davis, though he points out that the technology has yet to undergo independent tests.
Slightly further off is a battery for use in wind power generation. Conventional lead acid batteries can be connected to wind turbines to maintain output for short periods when the wind falls, but they cannot prevent wind generated power surges on the electricity grid. "The UltraBattery can smooth out the noise and provide energy for about 30 minutes, which is long enough to start up another generator," Lam says.
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Last Updated ( Tuesday, 14 July 2009 )
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