New infrared-emitting device could allow energy harvesting from waste heat

Researchers create first MEMS metamaterial device that displays infrared patterns that can be quickly changed


WASHINGTON — A new reconfigurable device that emits patterns of thermal infrared light in a fully controllable manner could one day make it possible to collect waste heat at infrared wavelengths and turn it into usable energy.

The new technology could be used to improve thermophotovoltaics, a type of solar cell that uses infrared light, or heat, rather than the visible light absorbed by traditional solar cells. Scientists have been working to create thermophotovoltaics that are practical enough to harvest the heat energy found in hot areas, such as around furnaces and kilns used by the glass industry. They could also be used to turn heat coming from vehicle engines into energy to charge a car battery, for example.

This illustration shows the room temperature MEMS metamaterial, which can achieve reconfigurable infrared intensities equivalent to a temperature change of nearly 20 degrees Celsius.
CREDIT Xinyu Liu, Duke University

“Because the infrared energy emission, or intensity, is controllable, this new infrared emitter could provide a tailored way to collect and use energy from heat,” said Willie J. Padilla of Duke University, North Carolina. “There is a great deal of interest in utilizing waste heat, and our technology could improve this process.”

The new device is based on metamaterials, synthetic materials that exhibit exotic properties not available from natural materials. Padilla and doctoral student Xinyu Liu used a metamaterial engineered to absorb and emit infrared wavelengths with very high efficiency. By combining it with the electronically controlled movement available from microelectromechanical systems (MEMS), the researchers created the first metamaterial device with infrared emission properties that can be quickly changed on a pixel-by-pixel basis.

As reported in The Optical Society’s journal for high impact research, Optica, the new infrared-emitting device consists of an 8 × 8 array of individually controllable pixels, each measuring 120 X 120 microns. They demonstrated the MEMS metamaterial device by creating a “D” that is visible with an infrared camera.

The researchers report that their infrared emitter can achieve a range of infrared intensities and can display patterns at speeds of up to 110 kHz, or more than 100,000 times per second. Scaling up the technology could allow it to be used to create dynamic infrared patterns for friend or foe identification during combat.

No heat involved

In contrast to methods typically used to achieve variable infrared emission, the new technology emits tunable infrared energies without any change in temperature. Since the material is neither heated nor cooled, the device can be used at room temperature while other methods require high operating temperatures. Although experiments with natural materials have been successful at room-temperature, they are limited to narrow infrared spectral ranges.

“In addition to allowing room-temperature operation, using metamaterials makes it simple to scale throughout the infrared wavelength range and into the visible or lower frequencies,” said Padilla. “This is because the device’s properties are achieved by the geometry, not by the chemical nature of the constituent materials that we’re using.”

The new reconfigurable infrared emitter consists of a movable top layer of patterned metallic metamaterial and a bottom metallic layer that remains stationary. The device absorbs infrared photons and emits them with high efficiency when the two layers are touching but emits less infrared energy when the two layers are apart. An applied voltage controls the movement of the top layer, and the amount of infrared energy emitted depends on the exact voltage applied.

Dynamic infrared emission

Using an infrared camera, the researchers demonstrated that they could dynamically modify the number of infrared photons coming off the surface of the MEMS metamaterial over a range of intensities equivalent to a temperature change of nearly 20 degrees Celsius.

The researchers say that they could modify the metamaterial patterns used in the top layer to create different colored infrared pixels that would be each be tunable in intensity. This could allow the creation of infrared pixels that are similar to the RGB pixels used in a TV. They are now working to scale up the technology by making a device with more pixels — as many as 128 X 128 — and increasing the size of the pixels.

“In principle, an approach similar to ours could be used to create many kinds of dynamic effects from reconfigurable metamaterials,” said Padilla. “This could be used to achieve a dynamic infrared optical cloak or a negative refractive index in the infrared, for example.”


Paper: X. Liu, W.J. Padilla, “Reconfigurable room temperature metamaterial infrared emitter,”Optica, Volume 4, Issue 4, 430-433 (2017). DOI: 10.1364/optica.4.000430


80 thoughts on “New infrared-emitting device could allow energy harvesting from waste heat

  1. They could also be used to turn heat coming from vehicle engines into energy to charge a car battery, for example.

    So this would make petrol engines even more efficient and attractive than electric.

      • It’s called ” Waste Heat ” for a reason.

        It is the garbage that is left over after the useful energy has been extracted, and it pretty much isn’t of much use for anything.

        There’s this Carnot efficiency thing that says how much good that junk is.


    • Well the Commission on Colorimetry of the Optical Society of America; presumably the same one as authored this paper, defines …… LIGHT …… as ” The psychophysical response of the HUMAN eye, to electromagnetic radiation energy in the 400 to 800 nano-meter range ” .

      That’s what it says in “The Science of Color ” published by that very commission.

      So l” LIGHT ” ….. BY DEFINITION ….. IS visible. it is not “heat” nor is it “thermal radiation.”

      It’s ALL ….. in your head ….

      So it isn’t even quantified in ….. ENERGY …. units, but in Photometric units like “candela ” and ” lumens ”

      So lets keep the science straight shall we.

      LWIR is NOT LIGHT.


  2. What we need is a device that can collect energy from LWIR, ie., from the so called back radiation that is beaming down upon us 24/7 365 days a year. According to K&T this has even more energy than solar, so this ought to be the engineer’s go to energy resource.

    Such a device would apparently be even more effective when it is cloudy. That would be a godsend for high northern latitude countries that have a cloudy climate such as the UK, Germany, Most of Northern Europe and Scandinavia.

    • Indeed, how stupid to install solar panels, while backradiation has on average twice the energy the sun delivers, and that 24/7.

      • Well said. It still boggles the mind that backradiation has twice the energy the sun delivers, but it’s science, right?

      • “Indeed, how stupid to install solar panels, while back-radiation has on average twice the energy the sun delivers, and that 24/7.”
        But the net radiation flow [in the black/grey body approximation of real surfaces] is the difference between the received flux and the emitted flux.
        If you suppose that the back-radiation can provide twice as much energy than the sun, you invented some kind of perpetual motion machine, breaking the laws of physics.
        But you can collect some of residual energy of a hot motor, provided that your IR device is cooler.

      • ” backradiation has on average twice the energy the sun delivers,”

        Not twice, about the same on average, and less at night. Nevertheless, VERY significant energy.

    • “so-called” back radiation!!! Ha ha, that’ll be the day, when we can extract twice as much energy from the cold atmosphere as we can from the hot sun! [According to Travesty Trenberth]
      Not only that, but we can harvest it 24 hours a day – what a godsend.

      • Another benefit of CO2. All this free energy being beamed from the atmosphere back to earth. Just waiting for someone to harvest it as a source of green energy. All that is missing is a $100 million dollar grant from the climate fund to WUWT to crowd source the project
        Take the money from the failed climate models and spend it on something so obviously more practical.

      • After all why do we need more than 1 climate model if the science is settled? If they don’t both give the same answer then 1 model is wrong and can be eliminated. If you don’t know which one is wrong how can the science be settled? In which case they are most likely both wrong. And if they both give the same answer there is no need for two. Spend the money instead on the WUWT LWIR green energy harvester project.

      • And as an added bonus the WUWT LWIR Green Energy Harvester Panels ®, when deployed in large numbers would not only solve the energy crisis, they would also block the LWIR from reaching the surface and thereby prevent global warming without any need to cut back on fossil fuel use.

    • Even better, when you go camping, take the large element out of your electric stove top before leaving home and put it in the camp fire and heat it red hot while plugging your extension cord directly into the two prongs of the coil. 1500 watts of pure 120 VAC to run your electric heater in the tent from the camp fire. Bring 2 elements and double the power for TV and internet. Pretty neat eh?

      • Leave your electric heater at home just put some rocks on the fire, and then move them into the tent when you are ready to sack out.


    • You just ignore simple physical properties: While downwelling radiation is about 300 w/m² IR radiation from the surface is about 370 W/m². so you have a net flow of 70 W/m² towards sky.

      Balance of radiative heat flow happens every hour in numerous situations on the world. Ignoring this will make us skeptics look dumb.

      Even if CAGW is a scam, we should be carefully how to explain it.

    • “the so called back radiation that is beaming down upon us 24/7 365 days a year. According to K&T this has even more energy than solar” Do you have a source for that info?

  3. Our industrial revolution has produced many many other sources of infrared radiation far better suited to the development of waste-heat recovery systems… like electrical induction…

    or infra-red LED arrays


  4. Needs a better write up. They mention could make use of waste heat and then goes into a mass of repetitive verbiage that leaves the reader wondering what the hades it is and what use it really has. Tunable IR patterns? OK, crank it up to maximize heat recovery and fix it there. And you use emf to move the plates closer together. How much energy gets used up for this maneuver?

    • Not sure how heat can be transmitted when everything is at the same temperature
      ‘technology emits tunable infrared energies without any change in temperature.’
      The rest looks like gobbledygook.
      Can’t find a publication date, but it is in April.

      • The disconnect is that IR photons are not heat. Heat is a/m (atoms and/or molecules) in motion. IR photons just happen to be very good for getting a/m moving.

        Most of our IR emitters until very recently were heat-based – i.e., they had some element with a/m in motion. Emit an IR photon, and those a/m slow down. (A resistance heater, for example, then gets them moving again – with electrons – to continue their emission.)

        This is the whole basis of the wildly misnamed* “greenhouse” effect. A high energy photon at a frequency the atmosphere is (mostly) transparent to strikes an a/m on the surface, which puts it into motion (OK, before I’m slammed by a witty nit – puts it into faster motion, only at 0.0000… K is there no motion). Later, this a/m emits a LWIR photon (actually a series of them) to slow down again – and the atmosphere is less transparent to LWIR. Which means the absorbing a/m in the atmosphere is now moving faster, and is therefore hotter.

        * Wildly misnamed because what a greenhouse does is interrupt the other mechanism by which an a/m loses heat – by collision with other, slower a/m. Air in a greenhouse is prevented from mixing with the colder outside air, so it keeps moving just as fast. Until it takes the other route to slow down and emits a LWIR, of course, to which most greenhouse glasses are actually transparent.

      • WR Thanks for that.
        The writers are talking about a ‘metamaterial’, presumably a solid, which emits infra red radiation without
        itself cooling, ie, it stays at the same temperature.
        They don’t appear to be talking about a gas.

      • Good for you WR.

        It gets very tiresome when people keep mumbling that old line that HEAT (noun) is transported by CONDUCTION, CONVECTION, and RADIATION.

        EM radiation at ANY wavelength or Frequency, does NOT convey ANY HEAT (noun), since no atomic or molecular material of any kind needs to be present to transport EM radiation, which can travel freely from a source at ANY temperature to a sink at ANY other Temperature; higher or lower.

        The EM radiation that is emitted by the earth and intercepted by the moon (cold), would if the moon was in a different place, get intercepted by the sun.

        Yes they do talk to each other in both directions, but they do so on different spectrum channels that depend on the Temperature of each one.

        You can do a very simple calculation of the amount of heat that you could conduct from the sun to the earth along say a copper rod, of any convenient diameter, suitable clad in a thermal guard ring, and ignoring the practical problem that at 6,000 K at the sun, the copper rod would evaporate; but do the calculation, and use type IIA diamond if you would like better thermal conductivity that copper.

        The resulting heat flux is microscopic; of the order of microwatt per square meter.

        Hint: type IIA diamond only has its fantastic thermal conductivity at low Temperatures.

        So we get NO HEAT from the sun; just first class electromagnetic radiation energy which can go anywhere it pleases, no matter what the temperature is.

        And PV solar panels are just about the only available transducer that can capture solar energy without immediately converting it into HEAT (noun) which is still WASTE energy however you cut it.

        By the way, just remember you fusion afficionados, that fusion turns that pure mass source energy into waste heat before you get to use it, so if the source is at ten million degrees, and you have to get it down below say 3,,000 kelvin to even think about starting to use it, just what do you think the Carnot efficiency of a fusion reactor would be.

        In the sun. the sun bottle takes care of transmuting the umpteen million core Temperature to a nice balmy 6,000 K surface Temperature, before it even thinks about sending us any energy.

        All of the numbers herein, are subject to veto by Dr. Svaalbard, who really knows what the real ones are.


  5. I want one that can harvest heat from two people in tge throes of passion.

    Just imagine: “But darling, we must, we need to save the planet!”

    No sarc at all

  6. I fail to understand how an article about a tunable IR emitter implies any sort of ability to work backwards.

    Do solar panels become lights when voltage is applied?

    • I share your skepticism.

      A new reconfigurable device that emits patterns of thermal infrared light in a fully controllable manner could one day make it possible to collect waste heat at infrared wavelengths and turn it into usable energy.

      We probably have a case where a PR flack heard something a scientist said and spun it into something completely unrelated to reality. My guess is that we don’t have to worry about this device collecting infrared waste heat any time soon.

      • Any conversion is theoretically reversible. But, like you, I am skeptical, at least from the snippets here – it is only rarely that the same device can be run both ways (at least with anything approaching the same efficiency – run electricity through a solar panel, and you will get a tiny bit of photon emission out of it).

      • Radio antennas (AM or FM) emit (or receive) photons too, which are not emitted by warm matter, but powered by a modulated electric source. If the “reconfigurable device” can emit IR, it can receive them.
        But by no mean it is certainly not possible to collect more energy than what reaches the ground from the sun without cooling something else. If this thing is the atmosphere, which has very few thermal capacity, it will cool very quickly.

      • If it does work by cooling the atmosphere, then it might make an effective replacement for air conditioners.
        Cool your house and get power instead of using power. I like it.

        Too good to be true.

    • Yes. Consider the photoelectric effect when used to actuate an automatic door. You can do it both ways. You also have sonoluminescence and chemoluminescence.

    • That’s my confusion . I saw they have some LED that works at some tunable IR wavelengths rather than just a thermal spectrum and some DLP like MEMS to control it , but what does that have to do with an IR photovoltaic ?

    • Some do; absolutely. Some of them emit very efficient infrared radiation and some will emit very bright visible light wavelengths.
      Silicon solar cells are not good LEDs, because silicon is an indirect semi-conductor, but Gallium Arsenide solar cells will radiate 900-950 nm IR radiation if you run a current through them in the forward diode direction.

      And Gallium nitride solar cells, will emit visible green and blue-violet visible light.

      In fact there is a III-V solar cell guru at UC berserkeley whose name unfortunately escapes my short term memory; who constantly states, in order to make a good solar cell, you first have to make a good LED; and he KNOWS how to do that.

      He also can make GaAs solar cells that are as thin as paper, and can be bent into a circle like a piece of Mylar film. And he just peels them off the expensive substrate, which he can then re-use to grow another solar cell. I’m embarrassed that I can’t recall his name, because he is one of the real people.


    • Well I left an extensive reply that got disappeared.

      YES YES YES Some solar panels DO emit Electromagnetic radiation when they are forward biased.

      Silicon solar cells will not, because silicon is an indirect semi-conductor; but Gallium Arsenide solar cells will emit infra-red, in the 900-1,000 nm range when forward biased.

      Look up Eli Yablonovitch under thin gallium arsenide solar cells.

      Eli, who is one of the real guys ( no not that Hare brained chap) says that in order to make an efficient solar cell, you first of all have to make a good LED. And he makes really god ones, that are so thin you can fold them up like a piece of paper. But do not suggest to Eli warping them into a cylinder like Solyndra thought was a great idea; Eli will read you the riot act.

      He peels has GaAs solar cells off the substrate, which is why they are so thin, then he uses the substrate over again to grow another one.

      GaN or InGaN solar cells will emit bright visible light EM photons, when you forward bias them, and in the blue-green-violet region. They can do that because those materials are direct band gap semi-conductors. No you will have to look that up for yourself if you don’t know what that means.

      So yes good solar cells are bidirectional. Those exotic III-V semiconductors are used to make multi unction multi band gap solar cells; typical three different materials stacked up, to give as much as 43% conversion efficiency as solar cells.

  7. ” thus realizing a spatiotemporal emitter capable of displaying thermal infrared patterns up to 110 kHz”
    and an array of IR LEDs can do it at 1 GHz.
    well, next invent a micro-electro-mechanical-relay and replace transistors!

  8. Why do we need to collect waste heat? Aren’t there better ways to do it? Why this article? Hazy memory of most basic physics – problem is T2-T1 for source and ambient. Thermodemonics 101. OK if it’s the exhaust of a gas turbine in a CCGT power station, not the waste heat from the steam cooling heat exchanger water or turbine itself, etc. Not much used to heat cars from exhaust heat after the Beetle gassed people, and there was higher thermal capacity engine cooling water to use, etc. “Low Grade” waste heat is notoriously difficult to do anything useful with, and expensive to harvest per joule. This smacks of the wholly innumerate science denial of green journalists using their smart phones to power the grid during shortages/peak offsets – only a good idea if it stops them communicating fake science to the unknowing.

  9. April Fools all month? No, since Arrhenius. But I can see uses for this charging my ebike from the black tarmac emitter! A dream come true?

  10. So they’ve created a crude, low-res video screen for that Predator monster in the movies. I fail to see how that has anything to do with “energy harvesting from waste heat.”

    Well, this is coming out of Duke, so I’m not surprised.

  11. can’t you tune waste heat using this device to emit most on the IR windows in the atmosphere so that waste heat isn’t trapped in a greenhouse but can escape to space. Solves CAGW as a stroke!

  12. I am always suspicious of articles that include the words “could” or “might”
    Much better to have a working device that “does”

  13. I applaud the research. Someday someone is going to come up with something that really works. Energy storage devices need that breakthrough for instance.

    I’m definitely not against solar or other alternative energy sources when it makes sense. Unfortunately in a lot of places it makes NO sense in its current use. Solar panels are a lot more efficient that they used to be which is great, but they still have that energy density thing to fight to be used on a grand scale.

    We have also come a long way in efficiencies. LED lighting is huge as are ultra efficient electric motors and even low voltage circuits in computers have had a large impact. I’m glad we are still plugging away (no pun intended) at this. It’s a real shame so much money has been wasted in the process.

    • I’ve been looking for better IR scene projectors, but don’t get where they are heading here. Can these conversions (IR radiation to visible light, then visible light to electricity) be more efficient than a conversion using a thermoelectric assembly with radiator fins facing the IR source?

  14. “could one day make it possible”

    Wish I had a dollar for every time I’ve heard that expression. Maybe I’m just becoming more cynical as I get old, but how many times have we heard such words published by an academic, only to never hear about the “breakthrough” again?

      • Not merely alarmists, but charlatans and hucksters in general.
        These articles are almost written like infomercials. Billy Mays would have been all over this one!

        BTW used for IFF (identify friend/foe) in battle? Why would this be better than numerous existing IFF systems currently operating? Radios and beacons exist in several frequencies, what does IR add?

        And we already have passive systems that are used for IFF they are called UNIFORMS and markings.
        Enemies could wear false colors? OMG like that has never happened before. They could just as easily use such a device to “emit friendly colors”.

  15. I’ve always been astounded that all the oil, gas, coal and nuclear energy which we ‘burn’ on earth does not raise the global temperature at all!

    • Same for the solar panels which capture solar energy that would normally sent out to space, and turn it to electricity which when used heats the earth. The issue is how much heating is involved relative to the total energy balance.

    • I second the motion. The Second Law of Thermodynamics tells us that to turn heat into useful work, you need both a high-temperature source of heat and a low-temperature place to dump waste heat. It also tells us that the efficiency of the process (the fraction of energy that can become useful work) depends on the ratio of those two temperatures. Planet Earth runs on the difference in temperature between incoming energy — sunlight at around 6000 K — and outgoing energy, infrared radiation into the blackness of space at, I dunno, probably around 290 K. (The net energy intake is essentially zero, of course; otherwise we would roast or freeze.)

      When someone proposes to get useful work out of infrared radiation, the first question to ask is “For second-law purposes, what are the two temperatures we’re operating between?” If the answer to that question is not laid out in plain view, the proposer hasn’t done his homework.

  16. I’m confused – how does a “New infrared-emitting device” (emphasis on “emitting”) capture/absorb heat?

    • I’m thinking the same thing.
      My common sense use of words isn’t meshing with science I guess.

    • It is (IMO) a type of photon trap. Photons come in but cannot escape. Of necessity such traps must be tuned. Radio “tank circuits” are an analog of this thing. Radio tank circuits can be used for receiving and for transmitting. The MEMS allows for changing the spacing and that means changing the wavelength of the trap. Emitting happens all the time by essentially all materials; but if you tune tiny resonators you will peak the wavelength that escapes from the device and this tuning is, in this case, mechanical.

      • Why must photon traps be tuned. Laboratory cavity black bodies, can absorb virtually all of whatever photons fall onto their aperture; they go in and like the cockroach Hotels they never check out.


    • Sorry Last time I looked at MEMS stuff was early 2000s as we were trying to deploy handheld devices with disk drives in them. The idea was you have a MEMS accelerometer detect that the device has been dropped and then you try to park the head ASAP..

      As for metamaterials Never did much work with those. Closest thing would be some of the work we did in advanced design in the 1980s around the idea of building self healing wings. It was more imagineering.
      Funny thing about imagineering is that engineers typically suck at it.

      I remember when I suggested that we take the pilot out of the plane and have an algorithm fly it. Stupid engineers thought it would never work.

      Any way.

      Scavaging energy will be a big thing in Iot. Check out some of the stuff my pal Phil Carmack is doing in chip design.

      There are lots of cool things coming… Ya’ll sit back, retire, in your comfy chairs and comment on blogs.

      I’m gunna go build more stuff.

      Wait till you see the next thing

      • Yeah, go build more “stuff.” The rest of us stoopid engineers will be selling real devices.

      • Say Mosh, the first Hard Drive I every owned was a 20 Meg 3 1/2 inch drive; can’t remember the brand name, but they eventually sold their drive to TDK.

        What was unique about their drive was the head parking. it literally was the first “cloud computing” because those heads landed up in the clouds, rather than down on the disk.
        A spring loaded head lifter raised the heads off the disk, when the power was off.
        When you turned the power on, the disks spun up without any head drag stiction, so very minimal motor torque needed to run the disk.
        Once the disks were up to speed, a solenoid closed and dropped the heads out of the clouds, so they came down and floated nano meters above the disks, riding on a cushion of residual gas.

        So the heads NEVER ever touched the disk, so there was no dedicated landing zone on some inside track. The much lower motor drive power meant lower heating, and the thing had much better g-shock specs than anybody else’s drive. I had it installed in an IBM PC-XT.

    • MEMS gyro and accellerometers are ubiquitous; pretty much every smartphone has them, radio controlled helicopters and drones use them. The magic is tuning fork, a vibrating element. Rotate the device but the plane of vibration won’t change (gyro) or it will resist change and the degree of resistance of change indicates rate-of-rotation of the device. To actually set it in motion you can use a piezoelectric crystal that changes dimensions in the presence of an electric charge or field.

  17. Some decades ago, there was a similar story about chips using waste low thermal energy with chips already used for small cooling systems, by reversing its working principle. All what you needed was a small temperature difference. Never heard anything again of that “invention”.

    Seems the same background idea. If that can be realised in a working prototype remains to be seen. The rewards anyway are huge: a gasoline car motor has a 25-30% mechanical yield, the rest of the energy from the gasoline is wasted as heat…

      • Thanks Michael,

        Didn’t know that it had already practical appliancies, besides of course thermocouples, but these have a very low energy yield, maybe enough if you can combine a few million on a chip surface, but then how to maintain enough temperature difference…

  18. As is the case in many meta-materials it is possible to create effects that you would not normally see in “normal” materials.

    Reviewing this paper it appears that they have created a “window screen” with openings of about 5 microns. This becomes the 1/4 wavelength and the screen is mostly transparent to shorter wavelengths ( 5 microns).

    This “window screen” is above a room temperature surface emitting at about 10 microns and since the screen is acting as an opaque barrier little 10 micron radiation gets through. The “window screen” by itself has very little thermal mass so it emits very little radiation (in absolute terms).

    Then they “pull” this screen down into contact with a continuous room temperature surface (emitting at say 10 microns) and the “window screen” disappears and the emitted radiation is now mostly 10 micron.

    So the unit effectively has “controllable emissivity”, you can make the emissivity at 10 microns “high” or “low”. Materials that can do this are unknown in nature and thus this is a “meta-material”.

    Since you can control the emissivity you can also control the absorptivity as well. This could/might/possibly/maybe… come in handy when “harvesting” waste heat.

    There is a reason “waste heat” has it’s name, yes, there is some heat there, and yes if you really really really want to recover it you can, but it’s worth is usually far less than the cost of “harvesting” it.

    Waste heat is like the few drops of water left in a sponge after a good ringing out, sure, you could put the sponge in a hydraulic press and waste a few horsepower getting those last drops out, but is it really worth your time ?

    Cheers, KevinK

    • Well it is waste heat that stops you from getting to zero K.

      And no matter how hard you try to use that waste heat for something useful, it gets more difficult the closer you get to zero.

      Most people consider waste time more valuable than waste heat so they just don’t bother with waste heat.


      • No George, the problem isn’t that it gets more difficult the closer you get to zero K. The problem is the delta between the heat source and the heat sink. The closer delta-T gets to zero, the harder it is to utilize “waste” heat.

  19. There’s a huge energy budget (over time) that’s missing, How much to produce? Lifetjme? Efficiency over lifetime? Cost of materiel? Etc, etc. Interesting from a scientific point of view, but way away from practical application.

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