Ultracapacitors Aim to Fill Energy Gap
Sidebar: Ultracapacitors Aim to Fill Energy Gap
News Story by Robert L. Mitchell
JANUARY 10, 2005 (COMPUTERWORLD) - Most notebook computers require about 12
watts of power during normal operations, but at boot-up, power demand spikes
well beyond that. Accommodating peak power demands in mobile computing
devices is a challenge for both battery and fuel-cell makers. Peak loads cut
into battery life while fuel cells, which are designed to generate power at
steady levels, simply can't respond effectively.
Ultracapacitors promise to improve efficiency in both cases by satisfying
the demand for short bursts of power -- from a few seconds up to a few
minutes. Ultracapacitors don't wear out like batteries do, can be recharged
quickly and can be reused thousands of times. "There is no chemical reaction
like a battery. It's just a charge stored in a capacitor," says Bobby Maher,
director of technical sales at ultracapacitor maker Maxwell Technologies
Inc. in San Diego.
Ultracapacitors such as Maxwell Technologies' Boostcap can supply short
bursts of power to supplement existing battery or fuel cell systems or to
deliver transitional power in the early moments of a power outage within a
UPS system. The model shown is the size of a standard D cell battery.
Some fuel-cell makers are including a small lithium ion battery in early
power packs to handle peak power demands. The battery is trickle-charged by
the fuel cell when not in use. "The problem is they want to get rid of the
battery," Maher say. He claims that many companies working on fuel cell
systems are including ultracapacitors in their designs.
Ultracapacitors will never work as a battery or fuel-cell replacement,
however. The designs have a very low power density. "The energy density is
very, very low. You need 10 times the size to get the same density as
lithium ion," says Isidor Buchmann, president of Cadex Electronics Inc., a
maker of battery charging equipment in Richmond, British Columbia.
Ultracapacitors also don't support sustained loads well because the power
curve drops linearly. "You can get 90% of the capacity out of a lithium ion
battery before it drops. With ultracapacitors, you can't use more than 50%
of the capacity [before it drops off]," says Buchmann.
Even as a peak power supplement, ultracapacitors are unlikely to make their
way into internal notebook computer power packs because the devices take up
too much space for the power generated. But they may be used in externally
mounted power packs, says Maher.
The use of ultracapacitors with fuel cells is still a long way off, says
Atakan Ozbek, an analyst at ABI Research in Oyster Bay, N.Y. "It takes a
long time to get from R&D to the commercial side," he says. "I don't know if
any [fuel-cell] companies are really going after it right now."