California magazine

Ethan Parker

In the race to create cleaner energy, one of the dark horses is heat conversion: capturing heat that we expend in making energy, and making it into more energy. It's made possible by a loophole in the second law of thermodynamics that says you can derive energy from a situation where there is a large difference in temperature—like, say, the surface of a running engine block. In an engine that uses 50 kilowatts to go up a hill, 1 kilowatt might run your lights and air conditioning.

There are already several gimmicky ways to accomplish heat conversion. For a few hundred bucks you can own a watch that runs off the heat in your wrist. But Arun Majumdar, a mechanical engineering professor, says widespread use is a ways off. The biggest obstacle is finding material that conducts electricity well, but not heat. That excludes most metals and plastics.

"This is not trivial," he says dryly. "Those [materials] are not easy to find."

But then again, the payoff isn't trivial either. Ninety percent of the world's energy production involves heat, and therefore the loss of heat. Finding a technique that harvests even 5 percent of this would mean billions of dollars in free power.

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