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Science

Material Breaks Record For Turning Heat Into Electricity 102

Posted by Soulskill from the hot-shocking-news dept.
ananyo writes "A new material has broken the record for converting heat into electricity. The material had a conversion efficiency of about 15% — double that of one of the most well-known thermoelectrics: lead telluride (abstract). For decades, physicists have toyed with ways to convert heat into electricity directly. Materials known as thermoelectrics use temperature differences to drive electrons from one end to another. The displaced electrons create a voltage that can in turn be used to power other things, much like a battery. Such materials have found niche applications: the Curiosity rover trundling about on the surface of Mars, for example, uses thermoelectrics to turn heat from its plutonium power source into electricity. That doesn't mean that the material is ready to be used on the next Mars rover, however: NASA has been looking at similar materials for future space missions, but the agency is not yet convinced that they are ready for primetime."
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Material Breaks Record For Turning Heat Into Electricity More

Material Breaks Record For Turning Heat Into Electricity

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  • heatsinks (Score:3, Interesting)

    by Anonymous Coward on Wednesday September 19, 2012 @05:43PM (#41393589)

    What stops this and materials like it from being used as heat sinks to recover some of the energy lost?

    • Doesn't the answer to such questions usually turn out to be "cost"?

    • Re:heatsinks (Score:5, Informative)

      by Anonymous Coward on Wednesday September 19, 2012 @05:51PM (#41393663)

      In a heat-sink you want to carry heat away from an object. A termoelectric is by definition a poor heat-sink because it requires a temperature gradient to work. This gradient means that the material is a poor conductor of heat. If it were a good conductor then both sides would quickly reach the same temperature and it would stop working.

    • Nothing really - that would be a very creative use to recapture some lost energy dissipated as heat. But at 15% efficiency it's possible that it's not feasible to add into any device. Besides the thermoelectric material you have to have an addition circuit to capture the energy and a battery storage. If the device already has a battery then it needs to be rechargeable. Its likely that this would act more as a trickle charge than a full fledge charger. In my reading of TFA I did not notice a temperature ran

      • Re: (Score:3)

        by Rei ( 128717 )

        One thing that this article isn't really consistent on is whether this is 15% of the Carnot efficiency for a given temperature gradient or 15% of the total difference in temperature between the two thermal reservoirs. Also, its performance under different temperature conditions can be very important for some applications, but that's not made clear.

        And for anyone saying "it's not an engine, Carnot doesn't come into account".... wrong. It amazes me how many people think this. Carnot's law applies to any ge

        • Carnot's law applies to any generation of work from heat, period. If you can break Carnot's law, no matter with what sort of device, you can create a perpetual motion machine

          While I don't see anything technically incorrect in your post, I'd just like to point out that Carnot doesn't apply to photovoltaics.

          And PVs are very relevant both because they can operate on infrared (something which the unsophisticated would just call "heat"), and also because they have been eyed for quite some time as a replacement (

          • Yes, it does apply to photovoltaics. Altough they can operate at the infrared, they can't turn into energy the emisions of a body at the same temperature that they are. And they lose efficiency when the gradient reduces, above what Carnot's law postulate as a minimum (in iother words, they are always worse than Carnot cycle).

            They'd be interesting at nuclear batteries because the origial radiation of a nuclear reaction has an extremely hight temperature. If you can deal with it without turning it into heat,

    • It should be noted that this article is about materials that perform the job of converting temperature gradients into electricity directly. Other methods of doing so are still more efficient (see your local coal, oil, gas, or nuclear plant.)

    • IIRC some laptops do exactly this to recover energy. However, it isn't terribly effective or cost-efficient. You certainly can, though (tends to reduce the effectiveness of the sink as well, although that depends on the exact design.)

      • I would love to know which laptop models are using this or similar heat recovery technology.

        • Hmm, now that I google it looks like my memory may have been bad. I remember there was plans to do this on some laptops (ultrabooks specifically, I think), but looks like they never followed through. Or I just can't find them.

    • Re: (Score:3)

      by macraig ( 621737 )

      No. You would be attaching a heat sink to one side of this material if, as is most likely, you were going to use it to cool something by driving current through it. That works in reverse when you "flip it over". The most likely first commercial uses of it would be to replace current "Peltier" thermoelectric devices in computer component "coolers" and the portable electric "ice chests" that are actually capable of heating or cooling contents. If this is a more efficient conversion without being much more

    • Re:heatsinks (Score:5, Informative)

      by Requiem18th ( 742389 ) on Wednesday September 19, 2012 @07:40PM (#41394531)

      Poor AC getting so mean comments.

      Actually you ARE right, but only from a certain point of view. Firstly, you are right that thermoelectric materials take heat away, and thus cool down whatever they are attached to.

      The critical point here is that merely cooling down is not enough for a heat sink. The heat sink has to be cooled down FAST. Faster than it's heat source is heating it. Thermoelectrics just can't turn heat into electricity fast enough to let a heat sink do it's job.

      So it's not really a matter of thermoelectrics heating up heat sinks, they don't heat them up, they in fact cool them down, what is heating up the heat sink is the heat source (say a CPU or a power engine).

      The problem is that no thermoelectric so far can transform heat intro electricity faster than a CPU turns electricity into heat.

      • Re: (Score:2)

        by jhol13 ( 1087781 )

        But it might me usable in cars. AFAIK there are already systems which generate electricity from exhaust heat.

      • Re:heatsinks (Score:5, Interesting)

        by Thammuz ( 970395 ) on Thursday September 20, 2012 @05:25AM (#41397103)

        Long time lurker, commenting because I know something about this one (doing my PhD in thermoelectrics).

        First of all, you _can_ use thermoelectrics to cool things like CPUs or fridges, but don't expect to generate any energy from them when you do it because you need to be putting electricity into the system, essentially carrying the thermal energy with it. You will cool one end and heat the other end. If you've ever heard of a Peltier cooler then you know what I am talking about.

        A good background can be found here: http://thermal.ferrotec.com/technology/thermal/thermoelectric-reference-guide/ [ferrotec.com]

        Second, this is something people have been messing around with the nanostructure of tellurium alloys for ~20 years or so, with the sole purpose of reducing thermal conductivity. The figure of merit for thermoelectrics is ZT = thermopower^2 x electrical conductivity x temperature / thermal conductivity. You can't increase electrical conductivity without reducing thermopower and increasing thermal conductivity (as there is a lattice and an electrical contribution). Thermopower is more or less a function of the number of carriers (lower is better) and their effective mass, so this is difficult to increase without durastic changes in the crystal structure or killing electrical conductivity. This leaves thermal conductivity. If you increase disorder in the material you make it harder for thermal energy to travel through it, which as lead to lots of research on how you manage this without messing up your carrier conduction. These are known as PGEC (phonon glass electron crystal) materials.

        Third, there are lots of applications of these (in heating/cooling and power conversion) if they can be made efficient and cheap. Anywhere you have a heat source pretty much. To use the classic car analogy, BMW, Ford, GE (amongst others) are looking at using a thermoelectric module to generate power for the car from the waste heat in the exhaust gases from the engine. This would increase the power of your engine by removing the alternator and also make the car lighter.

        The problem is the efficient and cheap part. These kinds of thermoelectrics are based on tellurium, an element about as abundant in the earth's crust as platinum, but to my knowledge isn't specifically mined for. Most other elements involved are toxic heavy metals (Pb, Sb, Bi, etc.)... so these aren't exactly nice things to have around or to make.

        This is where oxides come in. Made of lighter, more abundant, less toxic elements they are much cheaper to make (not just sourcing the materials, heath and safety too etc.), and are stable at much higher temperatures. As you know from Carnot, the higher the temperature a heat engine works at the more efficient it becomes; rather than 900 K (600C) you're looking at more like 1300 k (1000C) and upwards. Current high ZT oxides are things like NaxCoO2 and Ca3Co2O6, which have layered structures; one part is great at absorbing thermal energy (due to Na disorder for example) and the other is good at conducting electricity (like the CoO2 portion of NaxCoO2)

        TL;DR
        The way I see this paper: great proof of concept, PGECs are doing what they say on the tin and this will be great for low T applications. But for high power generation we need something more like the oxides which are cheaper, easier to produce, and work at higher temperatures.

      • I suspect what they were getting at is using waste heat from the CPU (and GPU). So instead of calling this material a heat sink, you have it draw heat away from the heat sink. It would only be one source of heat draw so the heat sink will still be efficient at what it does... but, you recover some energy in the process.

        You could use the energy for cool lighting effects in the case or to help power a cooling solution (fan?), or just feed it back in to the power supply to reduce the draw at the wall outlet. *

    • These devices need a difference in temperature, so in use they actually have heat sinks of their own on the cool end of them - they sit between a heat source and the heat sink, but I don't know that they'd conduct enough heat to the heat sink to be used on something like a processor. The use of thermoelectrics isn't new - much of the equipment the astronauts used on the moon were powered by RTGs, and the CIA lost some spy equipment in India that was spying on the Chinese back in '64 ( http://www.damnintere [damninteresting.com]
  • But what I can't tell FTA is whether or not the process of dis-ordering the material to prevent heat transfer also degrades the electrical conductivity. Obviously there is an over-all benefit, but I can't imagine that it is not affected at all.

    • Re: (Score:2)

      by mspohr ( 589790 )

      The article states that dis-ordering the material reduces heat transfer but not electrical conductivity. (They added some sodium to improve electrical conductivity.)

  • ...uses thermoelectrics to turn heat from its plutonium power source into electricity...

    I've love to drop a Plutonium power source into a Rover Discovery. There would be no place on Mars I couldn't drive to. As long as Chevron/BP/Shell never got wind of it.

    • Re:Plutonium Power Source?! Sweet (Score:4, Informative)

      by sphealey ( 2855 ) on Wednesday September 19, 2012 @06:26PM (#41393973)

      Discovery in fact uses a radioisotope thermal generator (RTG) with plutonium as the power source. It used a substantial fraction of the Pu-238 available for space missions.

      sPh

      • Re: (Score:2)

        by FunkDup ( 995643 )
        Did you mean

        Curiosity in fact uses a radioisotope thermal generator...

  • One potential use of these sorts of materials is to power Washington D.C. on the hot air generated by politicians. Hey, we might as well have them do something useful for a change!

  • I'll take some 15% more efficient LED bulb, and a 15% more efficient Central Heat and Air unit.. What about a 15% more efficient datacenter and laptop too while we are at it. The key to financial gain is either low cost energy or higher efficiency and the former isn't going to happen ever in my life, so yeah.. this is a good thing even back on Terra Firma. Of course real world applications may only have 8 or 6% gains, but still that's a big recovery if you suddenly added it to every gadget in the United Sta

    • Re: (Score:1)

      by rroman ( 2627559 )
      Well, I wouldn't agree that this material could be used in so many places to retrieve the used energy back. For example you might need to wrap it around the light bulb to get the energy back, but the material might not be transparent.

  • Efficiency in sensible units (Score:5, Informative)

    by johndoe42 ( 179131 ) on Wednesday September 19, 2012 @06:20PM (#41393923)
    TFA does a good job of using units that are incomprehensible to anyone who isn't an expert in thermoelectrics. But we can convert them...

    Considering a thermoelectric device with a cold-side temperature of 350K and a hot-side temperature of 950K, respective waste-heat conversion efficiencies of ~16.5% and ~20% are predicted.

    For a hot-side temperature of 950 K and a cold-side temperature of 350 K, the Carnot efficiency [wikipedia.org] (i.e. the maximum possible efficiency of any device) is ~63%. So this is somewhere between 1/4 and 1/3 as efficient as it could possibly be. Large generators, such as combined cycle gas turbines [wikipedia.org] are considerably more efficient, but these devices are small and silent. In other words: not bad.

  • - - - - Such materials have found niche applications: - - - -

    Niche applications: other than about 387 billion thermocouples measuring the temperature of everything around the globe.

    sPh

    • Re: (Score:2)

      by FunkDup ( 995643 )

      other than about 387 billion thermocouples

      You can't realistically generate electricity with a thermocouple. With this thing you can.

    • Re: (Score:2)

      by blueg3 ( 192743 )

      Thermocouples are generally made out of non-novel materials because they don't need to be efficient. (In fact, any pair of dissimilar metals joined correctly will form a thermocouple, but some are better suited than others.)

    • Thermocouples are not that common. Much more common are simple diodes.

  • If the cost is low enough, you could use this to replace conventional solar cells. Just place a thermocouple between two pieces of metal (paint the top one black). The top one will get hot and the bottom one would be shaded and air cooled. Instant solar cell. You wouldn't need to worry about keeping it clean or directing it toward the sun or anything like that.

    • Hard to get the hot side hot enough and to keep the cool side cool enough.

      • Re: (Score:1)

        by Anonymous Coward

        Hard to get the hot side hot enough and to keep the cool side cool enough.

        Duh, you just set up a heater to heat the hot side and an air conditioner to cool the cold side.

      • Re: (Score:2)

        by Belial6 ( 794905 )
        Put the cool side on the North facing side of the roof, and the hot side inside the attic. Even in a properly ventilated attic, it is almost always noticeably hotter in the attic than outside. The only question would be whether it was cost effective.

    • The efficiency is way lower than PV right now.
      But you can stick one on the back side of a solar panel with a heat sink. Those solar cells get quite hot in full sun.
      If it would be cost effective is another question of course.

  • I think even the simplest Stirling engines beat this thing out for efficiency, I think 30% is easily attainable and better engineered systems I believe can top 45%. The only issue with them is there is some maintenance (though NASA is working on eliminating that). I think the next generation of Radioisotope thermoelectric generators are supposed to use Stirling generators.
  • Let's start terraforming the sahara desert! We just need some of that water of the melting ice caps and we can get going. We'll use the energy of these heat-to-electricy-thingies to pump melted arctic water to the desert. And while we're melting the polar caps we might as well do some terraforming over there (south pole and greenland). It's gonna be great guys!

  • Diesel-electric generators are far more efficient than 15% at converting heat into electricity.

  • They had this in the McDLT*, and they threw it away! The fools!

    * - "It keeps the hot side hot and the cold side cold!"

  • NASA hasn't been pursuing better RTG materials, instead they've been developing Sterling engines to replace the Peltiers.

    The future of RTGs is in Advanced Stirling Radioisotope Generators (ASRGs):

    https://en.wikipedia.org/wiki/Advanced_Stirling_Radioisotope_Generator [wikipedia.org]

    See the "Proposals" section for a number of missions which planned (or currently do plan) to include them. With better luck, we could well have had them in current space-craft. Instead, it's one of those "any day now..." things. But once they

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