California-based Alphabet Energy plans to begin selling a new type of material that can turn heat into electricity. Unlike previous thermoelectrics, as such materials are known, it is abundant, cheap, and nontoxic.
Thermoelectric materials can turn a temperature difference into electricity by exploiting the flow of electrons from a warmer area to a cooler one. Thus, they can theoretically turn waste heat into a power source. But an efficient thermoelectric material has to conduct electricity well without conducting heat well, because otherwise the temperature across the material would soon equalize. Most materials that are good electrical conductors are also good thermal conductors, and the few materials researchers have been able to develop with good thermoelectric properties have been rare, expensive, or toxic. Alphabet Energy’s solution is tetrahedrite: an abundant, naturally occurring mineral that also happens to be more efficient on average than existing thermoelectric materials.
Ali Shakouri, a professor of electrical and computer engineering at Purdue University, says that tetrahedrite has promise because it doesn’t require the expensive up-front manufacturing that other materials require. “I think that’s kind of quite unique in thermoelectrics,” Shakouri says. “People look at so many materials, but the starting point has always been pure materials that they synthesize together.”
The fact that it’s abundant is another big plus, says MIT professor Mildred Dresselhaus. Other materials are made from elements so rare that they wouldn’t be available for widespread use.
According to data released by Alphabet Energy, tetrahedrite costs about $4 per kilogram, whereas other thermoelectric materials cost between $24 and $146 per kilogram. For now, the company is focusing on stand-alone generators, but founder and CEO Matt Scullin says it’s currently working with car companies to see if tetrahedrite can be used to harness heat from car exhaust.
Scullin says that other thermoelectric materials have typically achieved about 2.5 percent efficiency in cars, but tetrahedrite could reach 5 to 10 percent efficiency. “These aren’t incremental improvements,” he says. “They’re really huge improvements that make really significant impact.”
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