New Material Will Finally Let Us Convert Waste Heat to Electricity

By Sophie Bushwick | September 20, 2012 12:02 pm

thermoelectric material

If you’re reading this with a laptop sitting on your legs, you might have noticed that computers tend to warm up as they work, turning electrical energy into thermal energy. In fact, two-thirds of all the energy we use is lost as waste heat. Maybe, instead of just using the heat from your computer to keep your lap toasty, we should be harnessing that heat by turning it back into electricity. But the thermoelectric materials that convert thermal to electrical energy aren’t very good at their job. While they have some applications, the expense and inefficiency of current thermoelectric materials make them impractical for implementing at a large, power-saving scale. Until now: a new thermoelectric material might finally let us recover the energy lost to waste heat—at a reasonable price.

To be thermoelectric, a substance must let electrons flow through it while blocking the movement of heat. Its success at doing so reflects its efficiency as a thermoelectric material, and is represented by a value called ZT. For large-scale applications, experts estimate that a thermoelectric material needs to have a ZT of at least 2 when it’s at temperatures of around 900 to 1200 degrees Fahrenheit. Sure, that’s way hotter than your laptop will ever get, but in the range of many other engines’ temperatures.

One way to improve a material’s ZT is to tinker with its nanoscale structure, creating miniscule interruptions that prevent heat from flowing. But previous studies have tried this nano-structuring process on materials that naturally have relatively high ZT values, such as lead telluride—and at best, the new materials only achieved a maximum ZT of 1.8.

In the latest finding, published in the journal Nature, researchers took nano-structured materials and further slowed down heat flow by creating larger—but still minute—obstacles at the mesoscale, a scale slightly larger than the nanoscale. In lead telluride with both nano-structuring and meso-structuring, the researchers measured a ZT of about 2.2 when the material was heated to around 1190 degrees Fahrenheit.

That’s enough efficiency to let us finally start turning useless waste heat back into valuable electrical energy.

CATEGORIZED UNDER: Physics & Math, Technology
  • Chris

    So how efficient is that compared to a Carnot engine efficiency?

  • Rationalist

    @1 chris:

    The relationship between ZT and Carnot efficiency is temperature dependent, it is a function of both the heat source and the temperature that the thermoelectric device can reject waste heat to.

    At T(hot) = 500c and T(cold) = 30c, ZT = 2.2 corresponds to about 40% of Carnot, which is itself only 60%. So we’re talking 25% efficient. ZT= 3 is about 50% of Carnot.

  • Rationalist
  • Georg

    Chris,
    somewhat less than Carnot efficiency, what else?

  • Simon

    I have an application for this material!

    Is it available, or still at early stages of development?

    Please, if you can, let me know where to get this from?

    kind regards
    Simon

  • albert

    My brother worked on such thermoelectric material research last year at berkeley. He was researching on a material with a potential ZT value of 13. Obviously, the project.was a fluke

  • tanboontee

    A high proportion of useful energy ends up in wasteful heat energy. If this can be harnessed and converted to electrical energy efficiently, hopefully at a lower temperature, it will benefit everyone. How wonderful. (vzc1943)

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