Sidebar: Ultracapacitors Aim to Fill Energy Gap

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 along 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."