Most of us rely heavily on our cellphones, PDAs, and laptops, but we don’t generally see a dead battery as a matter of life or death. It’s entirely different, of course, for soldiers out in the field, whose survival depends on battery power for their global positioning units, communications systems, infrared goggles, and other electronic equipment [see photo, ” ”].
On a three-day mission, for example, a Special Forces soldier might lug along 12 kilograms of batteries. But now the military is developing a lighter replacement: micro fuel cells. These fuel cells could weigh half as much as batteries, and unlike the batteries, they could be recharged—or rather refilled. They would cost less, too—about US $800, says Rex Luzader, vice president of government relations at Millennium Cell Inc., in Eatontown, N.J., which is working on a fuel cell system with Protonex Technology Corp. of Southborough, Mass. For a 72-hour mission, a soldier might have to carry more than a dozen throwaway lithium-ion batteries, which would cost about $1040, Luzader says.
Micro fuel cells run on hydrogen, and the hydrogen sources being considered for them, chemical hydrides and methanol, have at least 30 times as much energy density as nonrechargeable lithium batteries. This means that more work can be done with less fuel.
The ProtonexMillennium Cell system has two parts. First, hydrogen is made in a replaceable cartridge and then introduced into the fuel cell itself, which makes the electricity. Millennium Cell specializes in the chemical cartridge, which it fills with sodium borohydride. Working with Protonex, which is developing a proton-exchange-membrane fuel cell, it hopes to develop a 30-watt power pack that weighs 4 kg—a prototype was delivered to the U.S. Air Force last March. A single cartridge could power the cell for 24 hours.
Greg Cipriano, vice president of marketing and military development at Protonex, says the power packs will be ready for testing this year. The U.S. Department of Defense has already invested $5 million in the technology.
The DOD is also investing in portable power systems based on different fuel cell technologies that offer weight and cost savings similar to the Protonex system’s. Last year, for example, the German company SFC Smart Fuel Cell AG, in Brunnthal, partnering with DuPont, in Wilmington, Del., delivered a methanol-powered fuel cell system for lab testing. Another company, Mesoscopic Devices LLC, in Broomfield, Colo., delivered two prototype 20-W systems to the Army Research Laboratory, in Adelphi, Md., in April. And UltraCell Corp., in Livermore, Calif., is being supported by the U.S. Army Communications-Electronics Research, Development, and Engineering Center, in Fort Monmouth, N.J., to develop a system that breaks down, or reformats, methanol to get hydrogen.
”The warrior is becoming more and more electronic, and future power use will only go up,” notes Cynthia Lundgren, a branch chief of the sensors and electronic devices directorate of the Army Research Laboratory. ”The higher [energy] density of a fuel cell will reduce the load soldiers have to carry.”
As a hydrogen source for micro fuel cells, chemical hydrides, fairly common in the chemical industry, offer advantages over methanol. Sodium borohydride, for instance, has more hydrogen by weight than methanol, which translates to a 12 percent higher energy density. A disadvantage of methanol is that it is volatile and flammable—although less so than hydrogen itself.
The systems’ volatility will be analyzed thoroughly during military tests, says Army fuel cell researcher Deryn Chu, who works under Lundgren. Fuel cell units will also be tested in the field at different temperatures and humidities, and kicked around in mud and dust. As an unofficial safety test, Chu ”took a plastic canister filled with methanol fuel to a firing range and had a bunch of shots fired into it,” says Lundgren. The result was promising: ”It didn’t burn.”
Another concern with fuel cells is that they are not good at providing bursts of power. This is why the military is also looking at hybrid systems that ”marry the advantages of fuel cells and batteries,” Lundgren says. The battery could be used only occasionally, to handle start-ups and heavy power loads, while the fuel cell recharges the battery and provides steady-state power.
Cipriano expects to have a hybrid fuel cell battery system ready for testing in 2007. The final version will contain a dry chemical hydride cartridge to which a soldier would add water in the field so that the power unit will be even lighter to carry.