back to article Boffins try to get closer to hot bodies

Scientists at the Massachusetts Institute of Technology have found a way of of increasing the amount of energy that can harvested from a hot body*. If the discovery lives up to the hype then it could possibly pave the way to devices that can use waste heat as a power source. Pointing out the potential of wasted heat, the press …


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  1. Annihilator
    Paris Hilton


    Hooray for that. Something I've never quite understood - energy is never created or destroyed, merely transformed. Potential energy in petrol for example almost always ends up as heat in the brake discs, or noise from the engine.

    So... why is global warming bad? Use the warmed up air, turn it into whatever form you want. We just need to get better at the exchange process.

  2. Filippo Silver badge


    Energy can't be destroyed, but it can be made unusable. Typically, this happens by converting it into heat and then spreading the heat around. Once energy is in the form of dispersed heat, it cannot be converted any more into anything else. It isn't destroyed, but it's useless. This is, in an oversimplified nutshell, the concept of entropy.

    A variety of devices can convert heat into more useful types of energy, but *only* if the heat is not dispersed (i.e. if two parts of the device are at very different temperatures). And they must disperse at least part of the heat to do so. This is, in another oversimplified nutshell, the reason for which entropy always increases and never decreases.

    For example, both the heat in the brake discs and the noise from the engine eventually end up as heat in the atmosphere. At that point, it's impossible to do anything with it. One *could*, in theory, build something that harvests part of the heat in the brake discs and maybe even the noise from the engine, but it would have to be a device that's physically located on the brake discs or on the engine.

    Once the energy is in the atmosphere, it's all but gone. The ability to turn heat into useful energy is based on temperature differences, and the temperature differences within the atmosphere are *tiny*. We still exploit them as wind power, but we all know how little power you can draw from that. The vast, vast majority of the energy just stays in the atmosphere, useless, until it radiates into space.

  3. Drunken

    Pesky Thermodynamics

    Annihilator! The problem is that heat can only be converted to useful energy if you have somewhere colder to dump the heat. The larger the temperature difference the more efficient the process. Therefore it becomes extremely difficult to extract energy from the ambient air temperature.

    See Carnot cycle for more info.

  4. Captain Thyratron

    Re: Annihilator

    Typically, you need a difference in temperatures to be able to extract useful work from a warm thing. Otherwise, heat doesn't flow. It's only important if the warm thing is warmer than something nearby. Q equals em-cee delta-tee and all that.

  5. Gene Cash Silver badge

    2nd law

    It's because the heat is energy in a least-ordered form. It's "too watered down and diffuse" in a sense. You can't just "turn it into whatever form you want" - you can exploit a temperature DIFFERENCE, like these quantum dots or thermocouples do, but it's not easy, and in the end you're just moving heat around and spreading it out even more.

    Energy is always turned from a more ordered into a more chaotic form. You go from the concentrated energy in chemical bonds to the random movement of atoms in the air. That's the 2nd law of thermodynamics.

    This is why the heat-death of the universe is inevitable. Eventually everything will be heat energy at the same temperature all through the universe and there will be no temperature differences to exploit for work.

  6. peyton?

    Perfect thing for Macbook Air owners!

    I've always had the suspicion that mine actually produces more heat than can be accounted for by the electricity it consumes. (Leave it to Apple to violate the laws of physics just to make something look pretty.) With this in place, I'm fairly certain I'll be able to unplug it for ever!

  7. DJ 2


    "Boffins try to get closer to hot bodies"

    They've been trying that for years, not worked yet.

  8. Graham Dawson Silver badge


    Energy is never created or destroyed, you're right, but it does become less useful as time passes. Energy is only useful as long as there's a gradient, with areas where there is high energy and areas where there is low energy. Once the gradient disappears and the energy is evenly distributed everywhere, you can have all the energy in the universe and not do a thing with it.

    In realistic terms that isn't a problem for us. We have sources of energy that can be prompted to release that energy with very little hassle.

    One area these things might come in useful is extracting solar energy. Every exposed rock and lump of concrete soaks up the sun's energy during the day and radiates it again, as anyone who's leaned on a building that faces south in the later afternoon will be able to tell you. Especially in the summer. Imagine being able to harvest all of that heat energy. Of course it would only work most effectively in the summer and in hot countries.

  9. Ignazio

    Sorry, not really...

    @Annihilator: unfortunately (sort of), global warming means more energy in the air and superficial ground, but nowhere near enough to be harvested with conventional methods, unless you want to chase the new hurricanoes with a windmill.

    Energy is never destroyed but thermal machines (whether they are fridges, boilers or these new things that convert heat into electricity) have theoretical efficiency limits, and even more pressing practical limits; that would be the reason why a fridge needs a power cable, and cannot run off the energy it subtracts to its content, to give a practical and quite extreme example.

    And to the journalist: come on, double battery time? that would mean 50% efficiency in converting residual heat, or something in that range of figures. Given that regular solar cells, which differ from these new cells on the wavelength of the radiation they capture, are between 10 and 20%, and visible light is more energetic than infrared light, that does not sound plausible. You might want to run it by a physicist to get the numbers right or at least believable.

  10. dr_forrester
    Paris Hilton

    We don't need no stinking title

    Well, gee, if you can get energy from hot bodies, why are we drilling in the Middle East and Alaska and places like that? Why not just go to LA?

    Paris, for obvious reasons.

  11. Anonymous Coward
    Anonymous Coward

    Hot bodies, universal energy source

    You can get a lot of energy from a hot body, especially if it's near and only for you.

    Even people who normally won't bother to do anything, become busybodies in no time.

  12. The Librarian


  13. Richard 102

    Don't Do It!

    It will lead to global cooling! We're all gonna die!

  14. Rex Alfie Lee

    Sorry, not really... Ignazio

    Actually Ignazio, modern solar cells have reached something like 44% efficiency, still not 50% but a lot more than you stated.

  15. Rex Alfie Lee
    Dead Vulture

    Richard, it's true, we are...

    You'll die long before the earth cools you to death...

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