Electricity From Heat Could Power Electronics

A thermoelectric generator could make army tanks and family minivans more fuel efficient by turning waste heat into electricity, and open up a variety of other uses, says the company that’s developing the generators.

GMZ Energy of Waltham, Mass., says it has demonstrated a module that produces 200 watts of electricity from the heat coming off a diesel-powered tank, a step toward building systems that will produce a kilowatt from such tanks. With the effort involved in transporting fuel to a battle site, diesel can cost the U.S. military upwards of $10.50 per liter ($40 per gallon). So using that fuel more efficiently will save the Department of Defense significant amounts of money, says Scott Rackey, GMZ’s vice president of business development.

The device is based on half-Heusler compounds, mixtures of elements that together have desirable thermoelectric properties.  GMZ built its device out of a compound containing hafnium, zirconium, cobalt, nickel, antimony, and tin, although Rackey says the company will eventually replace the hafnium with a less expensive element. They use a long-established technique called ball milling to grind the compound into nanometer-scale bits, then use heat and pressure to form the resulting powder into small disks. The materials used and the nanostructures created by the milling and pressing combine to improve a measure of thermoelectric conversion, called ZT, by 30 percent. That improved conversion rate is enough to make the device capable of converting about 7 percent of waste heat into electricity.

That might not sound significant, but with a new source of electrical power, a vehicle can use its alternator—normally the generator of electricity—less or not at all. That allows the engine to run more efficiently and use less fuel.

Rackey imagines other potential applications such as drilling equipment that uses the temperature difference between the crust it’s drilling into and surrounding seawater to generate electricity. A boiler with a thermoelectric device installed could produce power to run its own burner and circulator pumps, so it keeps working if power to the home goes out. There could also be a USB port to allow homeowners to recharge their electronics from the boiler.

“Because there’s waste heat in so many places, there’s lots of places we can put this functionality,” Rackey says.

Module Photo: GMZ Energy