Electronic Design

Fuel Cells May Beat Batteries For Backup

A fuel-cell technology by Metallic Power, Carlsbad, Calif., promises a more economical, space-saving approach to power. The company recently demonstrated a 2.5-kW/3-kVA backup power source based on a zinc-air fuel-cell system.

This technology generates power from zinc pellets and then recovers the zinc internally within the power source for the next cycle of operation. The rack-mounted source operates quietly while producing no emissions. Zinc also is nonflammable and benign to humans and the environment. The power source is significantly smaller and lighter than a conventional UPS equipped for similar runtimes.

Prototypes have operated up to five hours. Runtimes of eight hours or more are expected in the final product. As with all fuel cells, the runtime is a function of the size of the fuel tank, so power output and runtime scale independently. The company has proposed several variations of the power source with varying run times, and output voltages as well as ballpark numbers for size and weight. (See www.metallicpower.com for preliminary datasheets.)

The fuel cell's implementation is unique. Using zinc pellets, rather than zinc plates, permits scaling of the fuel tank so power and energy can be scaled independently. One fuel-cell design can be the basis for several power sources with different runtimes. Zinc pellets also are critical for fuel regeneration within the power source itself. They provide a form of the zinc that's readily circulated through the fuel-cell stack and through the regenerator for conversion from the zinc-oxide byproduct back to zinc.

Compared to the lead-acid batteries in conventional uninterruptible power supplies (UPSs), zinc-air fuel cells offer up to 10 times the energy density per kilogram and up to three times the energy per liter. As a result, zinc-air fuel-cell sources can be made smaller and lighter than UPS units.

Susan Connell, marketing communications manager at Metallic Power, says a 3-kVA UPS with eight hours of battery backup could occupy 65 in. of rack space and weigh 2800 lbs. An equivalent Metallic Power fuel-cell backup source would require roughly 20 in. of rack space and weigh about 300 lbs.

Metallic Power is seeking testing partners to determine the power source's optimum configuration. Field testing of prototypes is to begin early this year, with product introductions in 2003. For further information, contact Barry Eisenberg at (760) 476-8000, e-mail [email protected], or see www.metallicpower.com.

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