Carbon Nanotube Device Channels Heat Into Light (phys.org) 102
An anonymous reader quotes a report from Phys.Org: Rice University scientists are designing arrays of aligned single-wall carbon nanotubes to channel mid-infrared radiation (aka heat) and greatly raise the efficiency of solar energy systems. Their invention is a hyperbolic thermal emitter that can absorb intense heat that would otherwise be spewed into the atmosphere, squeeze it into a narrow bandwidth and emit it as light that can be turned into electricity. The aligned nanotube films are conduits that absorb waste heat and turn it into narrow-bandwidth photons. Because electrons in nanotubes can only travel in one direction, the aligned films are metallic in that direction while insulating in the perpendicular direction, an effect called hyperbolic dispersion. Thermal photons can strike the film from any direction, but can only leave via one. Adding the emitters to standard solar cells could boost their efficiency from the current peak of about 22%. "By squeezing all the wasted thermal energy into a small spectral region, we can turn it into electricity very efficiently," he said. "The theoretical prediction is that we can get 80% efficiency." The study has been published in the journal ACS Photonics.
Re:Would grid-scale batteries even be necessary? (Score:4, Informative)
Not exactly. Even through radiative exchange, entropy must be respected; the maximum efficiency you can gain remains proportional to the temperature difference between two radiating objects, and indeed is actually even lower than the limit imposed by Carnot's theorum for heat engines (due to endoreversible limits [wikipedia.org])
Now, there still does remain some potential, in that ground ambient temperatures and sky temperatures are not the same. A clear night might correspond to a sky temperature 20-40 degrees (celsius) cooler than the ambient air temperature, so there is some thermodynamic potential there to do work. But not a lot of potential. Remember that with the sun, you're exchanging between a nominal baseline of 5762K and 288K, respectively ;) Tc/Th is ~0,05 for the standard sun/earth exchange, vs. ~0,9 for a typical surface / clear night exchange. You're piling very low efficiency atop a very low heat flow.
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Not all "heat" is infrared radiation.
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PV cells 4x more efficient would change things over time, but not obsolete 90% of the oil market. However big promises rarely work out quite as hoped.
Re:That would be revolutionary... (Score:5, Interesting)
Depends on how you count the original promises, which depends upon how much attention you were paying in the first place.
Synopsis: a technological home run to end all home runs, without which Netflix would not now exist in a recognizable form.
Betcha weren't counting erbium-doped waveguide amplifiers. You should have been, but you weren't.
Re:That would be revolutionary... (Score:5, Insightful)
Betcha weren't counting erbium-doped waveguide amplifiers. You should have been, but you weren't.
Sure would be nice if the USA was producing erbium. China is where a vast majority of erbium is produced, as well as most rare earth elements. Despite their name they aren't all that rare, only difficult to mine when they earned that name. There's plenty of rare earth elements in the USA but because of the backward laws in this country it's very expensive to mine.
China can do their mining on the cheap because they treat the thorium and uranium oxides in leftovers of the monazite they mine as they should. It's basically just sand, so they pile it up in open air reserves. There's a little radiation from it, and it's toxic if you eat it, but still generally safe to handle with basic protections like gloves, dust masks, and goggles. Kind of like the same stuff they tell people that handle agricultural lime to wear, because that can burn the skin, eyes, and nose if exposed too much.
So, we can't mine for rare earth elements in the USA because the rules on handling thorium and uranium sand are those for weapons grade materials. Anyone that mines for rare earth elements in the USA have to pay for the disposal of this thorium sand as if it is highly enriched plutonium, smallpox, or mustard gas.
Thorium is worthless for making weapons. As evidence for this I give third world hellholes using centrifuges to enrich uranium instead of mining for thorium. If a nation wants nuclear weapons then they will indicate this by building centrifuges, not nuclear reactors. A modern nuclear reactor doesn't need enriched fuels, but even a primitive nuclear weapon will.
Out of a misguided concern for nuclear weapon proliferation we in the USA killed our own industries for nuclear power, rare earth elements, and likely many more. In the mean time we have China providing us with rare earth elements, stockpiling nuclear fuel, and developing an actual low CO2 energy industries in wind, solar, and nuclear power. Then there's nations like North Korea and Iran spinning their centrifuges for enriched uranium claiming they need this for their nuclear power industry, rather than open themselves to a global nuclear power industry where nations would be quite willing to build nuclear power plants for them, train their people in their construction and operation, help them mine for local thorium deposits, and outright give them tons of suitable fuel to get started so they won't need the centrifuges.
If the USA was serious about getting a low CO2 energy economy then they'd be building the infrastructure for domestic rare earth mining and refining, the factories for the solar collectors and windmill magnets that use those rare earth elements, and treating the thorium and uranium byproducts as a vital fuel source and not dangerous materials suitable only for dumping in a deep pit.
The USA is not serious about replacing coal and natural gas. When those in the federal government are serious then we will see rare earth mines open up and those coal miners will be in high demand for their experience.
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So you really want decent protection when dealing with this stuff, but piling mountains of sand in the open air where wind and water will carry it massive distances over unsuspecting ecosystems and communities is fine? Perhaps China isn't the best place to look to for inspiration - it's pretty well understood that the Chinese government is consciously choosing to poison their country hand over fist in order to spread the industrial revolution to their vast agrarian population. Basically following in our fo
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So you really want decent protection when dealing with this stuff, but piling mountains of sand in the open air where wind and water will carry it massive distances over unsuspecting ecosystems and communities is fine?
I don't know if we should be "fine" with this but it's far from dangerous to the ecosystem. They dug the stuff out of the ground to begin with, adding it back is no hazard. No more a hazard than the dirt was to begin with. Take a look at the properties of uranium and thorium oxides.
https://en.wikipedia.org/wiki/... [wikipedia.org]
https://en.wikipedia.org/wiki/... [wikipedia.org]
It's a sand that is insoluble in water so it's not going to contaminate any water supplies. It's very dense so the wind and rain won't take it far. Thorium is
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If you actually put it back *in* the ground, instead of dumping it on the surface then yes, that helps. But even then, unless it was sand and gravel to begin with you've thoroughly broken up nice stable rock into something completely water porous.
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Okay so you lock it up in concrete - that's great for a decade or ten, but concrete has nowhere near the long-term durability of most natural stone. That's the problem with pollutants that don't degrade - they never go away, so you have to think about the consequences of your actions on timescales that dwarf human history.
Now sure, you want to extract the uranium & thorium and burn it in reactors, I'm all for it, and it makes rare earth mining far more cost effective to boot. But first we need reacto
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Oh, and just FYI - now that China has a near monopoly on rare earths, it's not just environmental concerns that keep anyone else from opening their own mines. China is not shy about selling rare Earths below cost in order to sabotage the market for competitors trying to get established.
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"China is not shy about selling rare Earths below cost in order to sabotage the market for competitors trying to get established."
You know when governments give a shit they will protect their own industries. We don't have rare earth mining because we don't want it for 'nimby' reasons. (I hate acronyms!(just because I know what it is doesn't mean anyone else will))
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As the sibling post by an AC points out the government can put in place protections for the domestic production if China pulls a stunt like that. What China has done is place very strict export restrictions on rare earth elements that are not part of a finished product. If someone in the USA wants light and powerful magnets that contain these rare earth elements then they need to produce those magnets in China. That's assuming they can get only the magnet exported and not the speaker or generator that it
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Solar electricity doesn't compete with oil as much as it competes with coal. Coal is cheaper than oil for stationary power generation, but nothing really matches oil when it comes to compact, mobile energy.
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That's power - a fundamentally different property.
Power measures how much force you can bring to bear in this instant
Energy measures how long you can keep that up
Electrical motors are immensely powerful, with strength-to-weight and strength-to-volume ratios that blow ICEs out of the water.
Batteries though are what stores energy, and they are nowhere near the energy density of gasoline, alcohol, coal, sugar - pretty much all carbon fuels are pretty similar, at about 50-100x the energy density of Li-ion batte
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A well-tuned ICE is 30+% efficient at converting chemical energy into mechanical energy - sure, that pales compared to the 80-90% efficiency of batteries, but add in a 100x raw energy density, and you've still got a 30x advantage.
That's not to say that batteries aren't "good enough" for a lot of things, I'm a big fan of EVs, but you don't do anyone any favors by pretending they're even within an order of magnitude of the capacity of fossil fuels.
They're also expensive. You invoke the Tesla 2020 marketing
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Maxwell's Demon (Score:2)
How does a material become one way only for electrons?
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When they say one way I think they mean in one dimension only. The electrons can move longitudinally along the tubes (either direction) but they can't move in either perpendicular direction (through the walls).
Re:Maxwell's Demon (Score:5, Informative)
How does a material become one way only for electrons?
Diodes do it all the time.
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A set of single walled aligned carbon nanotubes is a "configuration of material", with much more complex configuration than a silicon PN junction.
Just because it's all carbon, while silicon needs a small amount of doping to operate as a diode, doesn't mean it is a simple amorphous blob of atoms with no electronic structure.
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DIODES, one way for electrons is what they do. semiconductor ones have been around since 1874.
nothing maxwell demonish about diodes.
Nanotubes can do the diode thing too.
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DIODES, one way for electrons is what they do. semiconductor ones have been around since 1874.
Hmmmm?????
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Lead sulfide, "galena cat whisker", I built an AM radio as a kid from a kit using one.
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I'm always amused at people who think everything electrical and electronic was done in the 20th century. Motors and batteries existed in the 1700s, The first fax was sent in the 1860s.
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"In 1874, German scientist Karl Ferdinand Braun discovered the "unilateral conduction" across a contact between a metal and a mineral. " -- wikipedia
it would be 26 years later that effect would be used in some radio receivers. Note the other type of diode at the time was thermionic, "vacuum tube", and it was invented within a year of that solid state device.
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Thank you for both posts. I'm an EE but have only a smattering of electronic history knowledge. Too busy studying other things. I wasn't aware that motors existed in the 1700s, but I know batteries (Voltaic Pile) and electromagnetism were discovered then. I think of 1800s as lots of electromagnets, (motors, generators, ballasts, magnets, Morse, telephone earpiece, Marconi set coils, Tesla coils, etc.) and some interesting microphones, etc. And then the thermionic emission device (vacuum tube / valve) -
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If you happen to work for Monster cable, you just draw a directional arrow on the cable.
80% efficiency (Score:2)
Holy fuck!
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Even if they can only deliver on half of what they claim, that's still at least a "holy fuck" without the exclamation mark.
The challenge is going to be in making this affordable, and mass-producible. Without that, these super-panels are going to be limited to space applications where weight is key and delivery cost dominates component cost.
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I suspect it will be like most semi-conductor gizmos. The first 1,000 or 100,000 cost an arm and a leg. Then they figure out how to make them "easily", build the factory, and they're a lot cheaper than (well, than the competition anyway).
The question here is how precisely does the fabrication need to be controlled, and just off hand, it sounds like "nano-scale should be good enough".
Re: 80% efficiency (Score:3)
I'm trying to figure out from the article whether that 80% is referring to a) the efficiency of the heat conversion to narrow-band photons, b) the overall efficiency of converting the "waste" heat fraction to electricity (heat to photons + conversion to electricity), or c) the potential final efficiency of the solar cell to convert sunlight to electricity. TFA makes it sounds like c), but knowing scientific journalism sometimes, it could very well be a) or b).
Re: 80% efficiency (Score:4, Interesting)
I RTFA yesterday and I'm as confused as you are. I don't think the article author understood what the scientists told him or her. My best **GUESS** is that "they" take "waste heat" which is basically non-coherent, broadband IR radiation and pass it through the nanotubes which act as a bandpass filter that emits only a narrow band of IR frequencies on the far side? That filtered signal can then (conceptually) be converted to electricity with 80% efficiency by a suitably designed cell? What happens to the rest of the IR which is rejected(?) by the filter? I have no clue. Reflected? Absorbed and re-emitted? Transported through a wormhole to a galaxy far, far away? I would think that almost all the energy in the IR would be in the portion that has been disappeared, not the portion that is passed through and converted to electricity. i.e -- the overall conversion efficiency -- total_IR_in to electricity_out would likely be **VERY** low?
Anyway, this sounds like it might have practical uses -- perhaps in sensors or communications. But it's far from clear to me that converting "waste heat" to electric power is one of the potential practical uses.
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It's fake news. Sure they did this in the lab, but people have tried to make carbon naotubes at industrial scale for decades. Everyone has failed; it's just too hard.
This is a nice science experiment, but it basically says: hey we did this! Now for the easy part, making this in an industrial, high throughput way! (which is actually the hard part, what they did is easy).
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I dug into it yesterday, and I got essentially what you got out of it.
Prior to this, there wasn't a good way to transfer the energy in broadband IR into electricity. (Heating water -> steam turbines is the current technology.) This solves half that problem by taking potentially 80% of that broadband IR and focusing it into a narrow band IR. That makes designing a way to harness it much easier.
Think of this as a lens for IR. Broadband IR hits the top, comes out the bottom focused.
Where does the rest go? I
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Not a lens? I think that if you want to focus IR, you can do that with a parabolic mirror? Maybe more like a "mechanical filter" in radio work that "stacks" a bunch of narrowband resonators to end up with a bandpass filter with a tailored bandwidth? You construct a bunch of filters with different center frequencies? And you follow each filter with a photovoltaic cell tuned to its center frequency?
Yeah. Maybe that would work ... maybe ... I'd anticipate a few annoying problems actually getting the piec
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From the summary it sounded like they were doing a frequency up-conversion.
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It's stupid and misleading.
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"Heat is the vibration of molecules rubbing against other molecules."
Sort of and close enough for many purposes. Strictly speaking heat is said to be the sum of all the energy of molecular motion in a substance. Vibration in solids and sometimes liquids. Kinetic energy in gases and sometimes liquids. And I believe that rotational energy in gases and liquids counts as heat as well.
I think the "vibration of molecules rubbing against other molecules" is closer to temperature (average molecular energy) than
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Rotational energy doesn't count a heat, whether it's in a fluid or not. But it turns into heat as it is dissipated against the surrounding stuff (of whatever nature). When heat is considered as molecular motion, part of the definition is "disordered".
That said, I believe that "hot" substances have a blackbody radiation in the heat area of the spectrum. As they cool, they head toward the radio part of the spectrum. So "mid IR" is the natural radiation of "blackbody" hot-on-a-human-scale objects (as oppos
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Phonon [wikipedia.org]
Low energy photons into high energy ones, Entropy? (Score:3)
This sounds like a good way to make a perpetual motion machine.
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Also, how does it handle minor, temporary temperature increases, like farts?
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Low energy photons into high energy ones, Entropy?
This sounds like a good way to make a perpetual motion machine.
Huh? We do this all the time, it's only a perpetual motion machine if you have an impossibly high efficiency.
A solar panel driving a UV LED converts low energy photons to higher energy ones.
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How much does it cost? (Score:5, Interesting)
I'll believe this when I see it on the market. I expect this to cost too much to bother.
This might make one of those pocket sized solar cell phone chargers 4 times more powerful but if it also makes it 10 times more expensive then I have my doubts on it selling to anyone but NASA and it's contractors.
I did some work on solar power stuff in university and it became clear that the goal was not raising efficiency but lowering costs. A 10% or 20% PV panel is fine for many cases because making something bigger is typically very cheap. A solar collection power plant out in the desert is already using real cheap land. At a maximum of about 1000 watts per square meter, under a midday sun, isn't that much to work with from the start. Add in weather and day/night cycles, and it's more like 100 watts on the average. Make it cheap and we can spread it out to where this shifting sunlight isn't as detrimental on the whole. Putting that money into something expensive and efficient just means putting your time, money, and materials, into a spot that might not have been a good choice because of some random local event.
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Go I say, go ahead and make this 80% efficient, cost be damned. *Then* with the economy of scale, cost *will* come down.
No, a cost reduction with scale is not guaranteed. What's also not guaranteed is a payback for your efforts. I'll explain.
What happens if I develop a solar PV cell that provides 100% efficiency. That's impossible I know but there's a hard limit of about 100 watts per square meter averaged over a day, this places a hard limit on the energy that can be obtained and therefore the value, in dollars, that can be produced. Suppose I discovered this solar cell but to make this cell I had to heat pure unobtaini
That's great, but... (Score:2)
we're bringing back coal! Your fancy cancer-causing solar cell gimmick that no one wants will never be as cheap as good ol' W. Virginia bituminous coal. #MAGA!
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we're bringing back coal! Your fancy cancer-causing solar cell gimmick that no one wants will never be as cheap as good ol' W. Virginia bituminous coal. #MAGA!
Maybe if we didn't have the stupid laws on the mining of rare earth elements we could put those coal miners to work mining for monazite. In that monazite is all kinds of goodies for making windmill magnets and these high efficiency solar PV cells. What makes it too expensive to mine here is that the thorium and uranium byproducts are worthless. Worse than worthless. Unless there is a market for the thorium and uranium then it is considered a controlled nuclear waste material and would have to be hauled
Refrigeration (Score:4, Interesting)
I know its cool to be talking renewable energy and global warming to get research funds nowadays but this (if it works) may have more application for refrigeration. Imagine ice boxes which dont need electricity to run. They just keep absorbing heat and emitting light. I can see brightly glowing refrigerator trucks driving down the highway.
most likely use (Score:2)
This invention is notable not because it harvests mid-infrared light, but that it does so across a wide bandwidth. Still, it is expensive for the application indicated in the article, which is supplement PV solar panels and improve their efficiency. It will be more useful to provide a drastic improvement in RTG (Radioisotope Thermoelectric Generator) performance. The Seebeck Effect generators currently used are not very efficient, yet is used because it is solid-state and long-lasting, which is a requiremen