Turning Heat into Electricity

Solar cells are so passe. The hot new area for research is thermocells, which convert waste heat into electric power.

Sorry, I couldn’t resist that one.

Power plants, factories, cars, computers–everything that uses energy in turn creates waste heat. If even a small fraction of that heat could be converted back into usable energy–in particular, electricity–the result could be dramatic energy savings and benefits for the environment. In principle, converting waste heat to electricity could double the battery life of cells phones or laptop computers, according to MIT engineer Peter Hagelstein.

A bunch of startup companies are working on just that challenge. They include Alphabet Energy, based in the basement of the Bancroft Hotel in Berkeley, which hopes to commercialize technology developed at Lawrence Berkeley National Laboratory “to tap into the US$1 trillion world market for the conversion of waste heat into electricity, with the potential to offset as much as 500 million metric tonnes of carbon per year.”

Others include MTPV Corp. in Austin, TX, GMZ Energy, founded by scientists at MIT and Boston College; Promethean Power Systems in Cambridge, MA, founded by an MIT grad; and established companies like Cypress Semiconductors and Komatsu.

Thermocells operate on the principle of the Seebeck thermoelectric effect, discovered in 1821 by the physicist Thomas Johann Seebeck. He found that heating one end of a metal bar created an electric current proportional to the difference in temperature at the two ends. Unfortunately, most materials that exhibit this property convert heat to electricity with extremely low efficiency, making it tough to create commercial solutions.

The race is on to increase conversion efficiencies and lower the cost of materials. Scientists at Lawrence Berkeley National Laboratory are using supercomputers to help identify relatively inexpensive and abundant materials. Their latest published work shows that all you greatly increase performance simply be replacing a precise percentage of anions with electronegative isoelectronic ions in highly mismatched alloys.

They make it sound so easy.

Another team of scientists just reported using carbon nanotubes to triple the usual efficiency of thermocells, without the cost of exotic metals such as platinum.

One of the co-authors of their new paper, Dr. Baratunde Cola at Georgia Tech, told me their new technology costs about $5.14 per watt, but that figure could easily fall in half with expected price cuts in nanotubes. Unlike solar cells, which generate full power only when the sun is shining directly on them, thermocells could operate 24/7 in many industrial environments, greatly reducing the cost of their power output.

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