2012-10-29

Salvaging Wasted Energy By Turning Heat To Electricity

Most of the power we generate gets frittered away as heat, but a new material can generate more power from that heat. The energy savings could be astronomical.

A lot of our energy doesn’t create power; it is wasted as heat. In the U.S., at least, half of the gas, oil, coal, and other fuels that we burn ends up dumped into the atmosphere without having powered anything. Inefficient technologies means the global figure is far higher.

Now, after two centuries of frustrating attempts, cheap, efficient, and sustainable materials are coming within reach that turn this heat directly into electricity. Known as thermoelectrics, these remarkable materials, first discovered in the early 1800s, turn temperature differences into electric current.

One of the first (and only) commercial applications was a Russian-built thermoelectric generator in the 1940s employing an oil lamp to heat up a generator to power a radio. After a burst of intense research, interest in thermoelectrics died as efficiencies languished below 5%—far below the threshold to make them economical for commercial energy recovery. A few applications were found: remote rural regions needing off-the-grid electricity and, most famously, space exploration. NASA has powered its Apollo, Pioneer, Viking, Voyager, Galileo, and Cassini missions by coupling a radioactive heat source with thermoelectric generators: The Mars rovers use such a setup to roam the red planet.

But nanotechnology is allowing us to build materials at the atomic-scale with the right mix of electrical conductivity (easy for current to flow) and resistance to heat loss. Publishing in the journal Nature last month, scientists at Northwestern University and other institutions finally broke through thermoelectricity’s historical efficiency limits, offering up "a realistic prospect of the recovery of a significant portion of waste heat."

"The material could signify a paradigm shift," says Northwestern University in a release. "Now, with a very environmentally stable material that is expected to convert 15% to 20% of waste heat to useful electricity [beating out the previous records of about 5%], thermoelectrics could see more widespread adoption by industry."

The new thermoelectric material is based on a common semiconductor, lead telluride, and ranks as the most efficient material of its kind (so far). Its properties are thanks to advances in fine-tuning the molecular structure of compounds to elicit precise physical properties. Applications range from utilities and heavy manufacturing—particularly those that generate a lot of heat, like cement factories and coal power plants—to the factories that make cars, ships, solar panels, and even computer chips.

With no moving parts, no CFCs, a tiny physical footprint, and hundreds of thousands of hours of useful life, the materials could become ubiquitous secondary power plants on anything that generates heat, which is almost every energy-generating process in our modern economy.

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