[HN Gopher] Cheap material converts heat to electricity
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Cheap material converts heat to electricity
Author : rbanffy
Score : 136 points
Date : 2021-08-03 09:13 UTC (13 hours ago)
(HTM) web link (www.sciencemag.org)
(TXT) w3m dump (www.sciencemag.org)
| SigmundA wrote:
| It says a ZT of 3.1, isn't that approaching 25% efficiency on par
| with more standard heat engines? Also more in line with say a
| solar panel for light to electricity.
|
| That kind of efficiency would be a big breakthrough if it where
| affordable, imagine the applications.
| mrfusion wrote:
| Could you put these on the backs of solar panels to capture
| some waste heat?
|
| Or tack them on ice engines.
| mrfusion wrote:
| You could also built completely silent refrigerators and
| freezers that last 100 years.
| tdeck wrote:
| How does this differ from using a Peltier module (already
| used in some mini fridges)?
| gpm wrote:
| I suspect you would still need a fan to cool off the hot
| side, but very silent, very long lasting, and the only moving
| part could be generic easy to replace fans.
| repiret wrote:
| Most current fridges have a fan on the cold side to
| circulate the coldness all around, and rely just on
| convection to pull away the heat (excepting RV propane
| fridges, which don't have a cold-side fan and have very
| uneven temperatures, but do have a hot-side fan because
| otherwise they don't work on hot days)
|
| Having had the evaporator fan go out in an old fridge once,
| I think you'll find fridge fans not as generic nor
| replacements as easy to find as you might hope.
| gpm wrote:
| > and rely just on convection to pull away the heat
|
| Interesting, I've definitely seen a normal sized house
| fridge with a fan on the hot side, but I don't know what
| is typical.
|
| > I think you'll find fridge fans not as generic nor
| replacements as easy to find as you might hope.
|
| Current generation probably not, but there's no reason
| these can't be your typical $20 computer case fan,
| especially on the hot side where there's no worries about
| condensation... for peltier elements you could even stick
| a off the shelf CPU heat sink on top (though presumably
| at scale you would build the heat sink custom).
| faeyanpiraat wrote:
| Time to make a new fan standard which everyone will use.
| Nasrudith wrote:
| Technically if you are willing to go overkill you could
| potentially use huge passive radiators but that would
| probably be a bit of a niche application.
| marksbrown wrote:
| Current peltier chips are barely a few percent efficient, break
| easily and require high temperature differentials. They're used
| in stove-top fans and RTGs. The latter should be Sterling engines
| to be ignorant mind. I don't doubt there are some interesting
| things to be accomplished by shaping the flow of heat conduction
| but I sincerely doubt it'll be energy generation directly.
| Thermodynamics isn't something you can just ignore!
| XorNot wrote:
| The history of moving parts in space missions (RTGs) is why
| Kepler's mission is degraded: keeping reaction wheels and other
| spinning things lubricated and moving when you can't get in
| there and service them is hard.
| chopin wrote:
| Why wouldn't airgapped bearings be used for this? Is it too
| heavy?
| Fordec wrote:
| The bearings end up cold welding at friction points in the
| vacuum of space is one issue.
| kwhitefoot wrote:
| > Those could be installed everywhere from .. water heaters .. to
| scavenge some of the 65% of fossil fuel energy that winds up as
| waste heat.
|
| Modern condensing gas boilers for domestic use are better than
| 90% efficient, the exhaust gas is very cool so I don't think that
| thermoelectric devices have much to offer there.
| marktangotango wrote:
| Isn't the minimum exhaust temperature the same as the
| temperature of the heated water? How can it be less?
| namibj wrote:
| intake air preheating and cold return water preheating come
| to mind
| dhajzhz wrote:
| If the exhaust is too cold the water vapor condenses out left
| with a puddle of acid (the acid is from the trace sulfur in
| the Nat gas)
|
| Also, cold exhaust doesn't exhaust (since it cant rise
| through a density change). So, if your exhaust is too cold,
| it will collect in your basement (CO2 should be a bit denser
| than air, so absent any drafts it'll collect)
|
| The previous owners of my house installed my high efficiency
| stove improperly using the old brick flue. The fumes
| eventually ate away at the mortar and a few bricks fell I'm
| clogging it.
| enkid wrote:
| If I understand the article correctly, you're talking about two
| different things. Something can be efficiently heated but if it
| cools down all of that energy is effectively lost. This device
| would allow you to recapture some of that energy that is lost
| to then reheat the water. Think of it more as active insulation
| than a better heating element.
| leoedin wrote:
| I don't think that's quite how it works. This device (or any
| thermoelectric generator) converts a fraction of the heat
| energy flowing through it into electrical energy. That means
| energy has to flow through it for it to work - essentially
| the opposite of insulating. Using this device, by definition,
| will result in the original hot thing being cooler, and the
| "cold end" (normally the outside world) being ever so
| slightly warmer.
|
| The place this would be useful is in capturing otherwise
| unusable energy from low grade heat waste. For example, the
| output water of a steam turbine might still be "hot", but
| there's very little you can do with it - it's in the wrong
| place for heating houses, it's too cold for steam turbines.
| Generally that energy is lost to the air.
| NohatCoder wrote:
| That is because the 90% is heat efficiency, this is for
| extracting electricity, which is much harder.
| IanCal wrote:
| Also, that's not necessarily more efficient for heating when
| compared to heat pumps. With a SCOP of 4, converting gas to
| electricity at 35% efficiency is better than using it for
| heat at 100%.
| lizknope wrote:
| This Old House on PBS routinely installs systems over 95%.
|
| There are systems here listed at 98.5 AFUE
|
| https://www.energystar.gov/products/most_efficient/furnaces
| londons_explore wrote:
| Fossil fuel systems 'cheat' a little in efficiently metrics
| by using the 'Lower Heating Value' of burning the fuel.
| That's the amount of energy the fuel contains if you assume
| that the resulting water produced in combustion is released
| as water vapor.
|
| However in real boilers, there is no need for this - by
| condensing that water vapor back into liquid water you can
| get more energy out. That's the 'Higher heating value'.
|
| When measuring efficiency, we always use the lower heating
| value, whereas we ought to use the higher heating value.
| Therefore a "98% efficient furnace" is actually more like 88%
| efficient when considering the higher heating value.
| yetihehe wrote:
| If you had CHEAP device, which uses exhaust at 70C to still
| generate some energy, this could be useful. This way, your
| exhaust could be lower temperature than your heated water.
| Currently this is not feasible, because such devices are not
| cheap enough.
| makomk wrote:
| Yeah, I think the more conventional way to integrate heat-to-
| electricty into heating applications is the reverse of that:
| feed the high-grade heat from fuel combustion into the
| converter, and use the rejected waste heat from it for heating.
| This gives a big enough thermal gradient to get useful amounts
| of electricity out, and the waste heat can still be plenty hot
| enough to be used for heating.
| billpg wrote:
| Heat is energy.
|
| In summer, the sun (rudely) gives me excess unwanted heat in my
| house. I need to expend even more energy to get that heat from
| inside to outside my house. (We call this process "Air
| Conditioning".)
|
| What would be ideal is if the heat energy could be converted into
| some other form of energy that I could dispose of. Maybe if I
| could turn it into electricity I'd put a lightbulb in my window
| and shine the converted heat energy away.
|
| I don't really care if that process is inefficient because that
| heat was completely free and unasked-for. I don't need to do
| anything useful with the converted heat energy, I just want it
| gone. If the process of converting heat to a disposable form of
| energy can be done for less energy than air conditioning needs,
| then its worth doing.
| elzbardico wrote:
| I don't see why people are downvoting you, as you are basically
| wanting to avoid wasting good energy with air conditioning.
| Maybe people thought your tone was blasfemous?
| Ajedi32 wrote:
| Because what GP is proposing is thermodynamically impossible.
| The second law of thermodynamics states that heat naturally
| flows from hotter to colder regions. You can't just magically
| convert a static pool of heat to light and beam it somewhere
| else with no energy input. It's like suggesting that we
| generate electricity by rolling stones uphill; it just
| doesn't make sense.
| billpg wrote:
| I don't know about blasphemy. My intended tone was "telling a
| joke".
|
| I know what I proposed would require our understanding of
| thermodynamics to be wrong, but this is in response to an
| article about a material that converts heat into electricity.
| I would love to hook up this material to a lightbulb in my
| window and save money!
| foobarian wrote:
| I did get your snark but also half-thought that you were
| alluding to covering the house in solar panels. Which
| would, in an indirect way, remove the heat from your house
| and convert it to electricity :)
| bernulli wrote:
| People are downvoting because billpg essentially wants a
| perpetuum mobile, something that creates useable energy just
| from the presence of a high temperature reservoir. This
| violates the 2nd law of thermodynamics. Heat does not equal
| usable energy, what you need to extract something useful is a
| temperature difference.
| billpg wrote:
| I don't care if the energy is useful, I just want it gone.
| oehpr wrote:
| It sure is tempting to think of heat as just energy. I mean it
| is. Of course. But the kind of device you're talking about is
| like Maxwell's Daemon. The article is talking about a step
| towards making an inexpensive thermocouple. These require
| temperature differentials, not just heat. And you don't want to
| be drawing power from the temperature differential in your
| house ;)
| tialaramex wrote:
| > What would be ideal is if the heat energy could be converted
| into some other form of energy
|
| That would be nice, wouldn't it. If you ever build a universe,
| you should definitely implement that. In _this_ universe the
| laws of thermodynamics specifically forbid destroying heat, or
| converting it into something else.
|
| Heat will naturally spread out evenly over time, but if we
| would prefer to do the opposite, moving heat where we want it
| (or away from where we don't want it), we need to use a _heat
| pump_ which expends energy to do that, and that energy produces
| further waste heat which, yes, we also need to move. This is a
| _core principle_ of how our universe works. Nobody is going to
| invent a new material that violates the laws of thermodynamics,
| for the same reason nobody is going to find an even integer
| that was hiding between 2 and 4 somehow without us noticing it.
| grishka wrote:
| > In this universe the laws of thermodynamics specifically
| forbid destroying heat, or converting it into something else.
|
| But wait, what does a Stirling engine run on? Or a steam
| engine? You clearly can get _some_ energy out of heat.
|
| Also, objects that are hotter than absolute zero radiate
| infrared light -- and you, in principle, could convert light,
| regardless of its spectrum, into electricity.
| bernulli wrote:
| They run on temperature differences, that's how you get
| usable energy out of it. Google Carnot engine, there's even
| a super simple way to find the maximum efficiency just from
| the temperatures!
| grishka wrote:
| Or you could have a battery and store that energy to supply
| your house with electricity, thus reducing your bills.
| billpg wrote:
| That would be useful energy, which thermodynamics says is
| impossible to extract from heat.
| grishka wrote:
| But you clearly can heat something and extract useful
| energy from its IR radiation.
| matheusmoreira wrote:
| So I can use electricity to mine cryptocurrency and convert the
| excess heat back to electricity? I wonder how efficient such a
| thing would be.
| sudhirj wrote:
| Depends entirely on how the system was laid out I guess. If
| you're in a cold region, say Iceland, and water-cool your
| miners entirely by running the hot water against a
| thermoelectric system with the one side out in the snow, maybe
| 60%?
| zionic wrote:
| I wonder why you don't have a miner-hot-water heater? Use
| energy to mine and the waste heat to keep your tank warm.
| yetihehe wrote:
| I was trying to find article about some random guy who used
| mining rig to suprcharge his heat pump [0] but found
| commercial solutions [1]. Just search "miner heater" on
| google.
|
| [0] https://medium.com/swlh/heating-my-home-with-crypto-
| mining-1...
|
| [1] https://greenheat.systems/
| yjftsjthsd-h wrote:
| There have been stories of people heating houses that way,
| actually.
| matheusmoreira wrote:
| I once joked here about crypto showers. Electric showers are
| ubiquitous where I live, it's just a dumb resistance heating
| up water. Could be replaced with a ton of processors mining
| cryptocurrency and heating up the water as a side effect.
|
| Are you telling me this sort of thing already exists today?
| davgard wrote:
| I'm quite curious if this works efficiently as well. The
| question is, is the amount of excess heat that the rigs give
| off and sustain the energy needed to keep the mining rigs
| working 24/7?
| edhelas wrote:
| Elon Musk breath intensifies SSSSSS
| pcdoodle wrote:
| I wonder if these researchers would help productize their
| findings into a kick starter prototype kit, would this advance
| faster due to the hive effect?Seems like every innovation stops
| "3 feet from gold"
| 988747 wrote:
| Finally! Now we can have an air conditioner that does not require
| a pipe to blow the hot air outside. Like truly mobile unit.
| layoutIfNeeded wrote:
| That's thermodynamically impossible.
| jkgktnrnfnf wrote:
| Not true.
|
| For example you could convert the heat into photons (infrared
| radiation) and beam that out of the room without needing a
| pipe. You would probably need an infrared transparent patch
| on the window to aim at.
|
| https://spie.org/news/5129-a-metamaterial-to-convert-heat-
| to...
| flavius29663 wrote:
| Why? You could theoretically take out energy from the room in
| the form of electricity
| layoutIfNeeded wrote:
| You can't. The second law of thermodynamics prohibits it.
|
| "It is impossible to devise a cyclically operating device,
| the sole effect of which is to absorb energy in the form of
| heat from a single thermal reservoir and to deliver an
| equivalent amount of work."
| jodrellblank wrote:
| How does having a hot side of a piece of material and a
| cold side of a piece of material come under "cyclically
| operating"?
| rpmisms wrote:
| Perhaps not an equivalent amount of work, but if we could
| capture some of the waste....
| vlmutolo wrote:
| Unfortunately we'll always need the pipe to blow air outside.
| The heat has to go somewhere. Even with this invention, if
| they're converting heat to electricity, they will have to
| release at least as much heat as they converted to electricity.
| john_yaya wrote:
| Indeed, this can be demonstrated by running current through a
| plain old Peltier cooler without a big chunky heat sink
| attached. At first the cooler will have one side heat up and
| the other side get quite cold, but within a few minutes the
| entire block becomes evenly warm.
| noselasd wrote:
| Eh, doesn't all modern air conditioner just do heat
| exchanging? no need to actually blow the air out - but yes
| you still need a pipe for the heat exchanging medium
| layoutIfNeeded wrote:
| Nitpick: you can't convert heat to electricity. You need a heat
| _differential_.
| srean wrote:
| Nitpick on nitpick -- you absolutely can convert heat energy
| into electric energy. A dynamo on a heat engine does exactly
| that. What suffices is _temperature_ differential.
|
| It is a terrible analogy, a modern physicist would prefer being
| caught dead rather than using it, but one can think of heat as
| a liquid (traditionally called caloric ) stored in a vessel.
| Temperature is the level of the liquid. For flow you need
| another vessel where the level is low, that would allow flow of
| heat from a vessel with higher level to a lower one and one can
| then convert that flow into power of a form one desires. Its
| possible to go in the opposite direction also, that's called a
| heat pump. Charge and voltage would be another (incorrect) way
| of thinking about heat and temperature.
| Tepix wrote:
| How much of a temperature differential is needed? Could this be
| used on a boat to take advantage of cool water and warmer air?
| cblconfederate wrote:
| I know a very cheap material that can also be used to convert
| heat differentials to electricity , called wind
| xyzzy21 wrote:
| TE devices are SPECTACULARLY inefficient. Carnot's Law applies
| and the thermal tolerance of all TE material are limited. You are
| lucky to get 5% on a good day. You still still a heat source and
| cold sink just like ALL OTHER heat engines and the efficiency is
| limited by the difference in temperature. There is no cheating.
| There is no magic.
|
| Selenium is moderately available but it is toxic waste when you
| need to replace it (all things have finite lifespans) and then
| need to dispose of the discard.
| calgoo wrote:
| I wonder if you could get it small enough to use with CPUs. Could
| extend the battery of a laptop for example. I'm also thinking of
| AC units, where it could lower the power consumption at the same
| time as lowering the heat we diffuse into nature, especially in
| big cities where the most rooftops feel like saunas.
| grishka wrote:
| When it was unusually hot over here, I was thinking about this.
| We can convert nearly every kind of energy into electricity and
| back. But for heat, for some bizarre reason, this only works
| one way. A lot of processes generate it, but you literally
| can't convert it into any other form of energy. You have to
| transfer it somewhere where it won't be as much of a problem.
|
| It would be very nice to have an AC where you don't need to
| deal with that. I thought about many ways to get rid of heat
| without having to dump it somewhere, but thermodynamics is such
| a terrible thing.
| blueblisters wrote:
| > I thought about many ways to get rid of heat without having
| to dump it somewhere, but thermodynamics is such a terrible
| thing.
|
| This is likely a stupid question but temperature is a
| statistical property describing the energy of molecules
| right? Is there no way to tap the energy of the molecules for
| useful work without having a temperature difference?
| davidinosauro wrote:
| You might want to read about Maxwell's daemon [1]. I came
| across this a few weeks back, two links away from the HN
| homepage.
|
| I found it intreaguing and read more about it but I can't
| quite umderstand the proposed solutions, likely due to my
| lack of background in thermodynamics.
|
| [1] https://en.m.wikipedia.org/wiki/Maxwell's_demon
| wiredfool wrote:
| Thermodynamics -- you can't win, you can't break even, and
| you can't even leave the game.
| yetihehe wrote:
| > I'm also thinking of AC units, where it could lower the power
| consumption
|
| Nope, if you use this on hot side, AC will have to work more to
| get rid of heat, but this device will still provide less power
| than ac must now use. Design criterium for AC's is that hot
| side should be as cool as possible (so it has a big fan to cool
| it down), but thermoelectrics require hot side to be as hot as
| possible.
|
| AFAIK compressor units are still way more efficient than this
| device, so no reason to bog them down with something with less
| efficiency.
| wiredfool wrote:
| I don't think that's right.
|
| The solid state methods can sustain a temperature
| differential with a given power/heat flow. If the hot side is
| cooler, the cold side can be cooler, or less power is
| required.
| s1artibartfast wrote:
| Thermoelectric elements add resistance. You are literally
| adding a giant resister between the hot and cold side,
| which decreases the thermal Flux for a given temperature
| difference.
| yetihehe wrote:
| If you insert something between hot side and air to extract
| energy, there will be more heat resistance and lower heat
| transfer, but this resistance will be bigger than what you
| get from your energy extracting device.
|
| If you use that new device as a cooling enchancer, you will
| have to provide some power. If your first cooler user more
| efficient method, you should just make bigger unit using
| more efficient method, because otherwise whole apparatus
| will be less efficient.
| [deleted]
| France_is_bacon wrote:
| I'd be interested, too.
|
| I once read in some article that CPUs have the same power
| consumption as equivalent output of a nuclear reactor, based on
| size, of course. So the 1 inch of a CPU takes as much energy as
| 1 inch of a nuclear fusion output from a nuclear reactor.
| Again, I don't know if this is true, but if it is, that's a lot
| of heat energy, given the number of computers in the world.
|
| But maybe I remember wrong, this was probably 15 or 20 years
| ago that I read this.
| fy20 wrote:
| Must have been a Pentium 4.
| guidopallemans wrote:
| Time to air-con the world, I guess
| pjc50 wrote:
| > The polycrystalline tin selenide the team makes is spiked with
| sodium atoms, creating what is known as a "p-type" material that
| conducts positive charges. To make working devices, researchers
| also need an "n-type" version to conduct negative charges.
|
| This is literally inventing half a solution. Shockley didn't go
| to the press when he'd built half a diode.
|
| (OK, this is snarky, but I think this is another case where
| people need to understand the difference between "a small but
| valid advancement in the art" and "actual products". As a
| materials science paper this is valid.)
| JoBrad wrote:
| > Zhao's team recently reported making an n-type single-crystal
| tin selenide by spiking it with bromine atoms. And Kanatzidis
| says his team is now working on making an n-type
| polycrystalline version. Once n-type and p-type tin selenide
| devices are paired, researchers should have a clear path to
| making a new generation of ultra-efficient thermoelectric
| generators.
| optimalsolver wrote:
| So write the paper after that's all done.
| helixc wrote:
| You don't understand the difference btw a research paper
| and a product launch. A paper is to provide inspiration. In
| this case, a high ZT p-type crystal may indicate a new
| mechanism that can be applied to searching / designing new
| thermoelectric materials. It's not for selling you a
| working device that can be put in your shopping cart.
|
| (I did research in nano thermoelectrics and published a few
| papers in this field)
| [deleted]
| throwaway4220 wrote:
| In defense of parent though it does not say "can" or
| "will" convert. News and views should have reflected that
| so it's really not the fault of the original paper
| authors.
| robbedpeter wrote:
| Isn't graphene a high quality p type material as well?
|
| What makes a material p or n?
| robbedpeter wrote:
| Kinda answered my own question with some searching - looks
| like p type has lots of electrons, n type has lots of holes,
| and graphene oxide (GO) makes an excellent and simple to use
| n type material.
|
| Graphene can be modified by changing its topology to be p or
| n, but GO is n by default. Do electron and hole features have
| to match in these constructions?
| steve_b wrote:
| I think that's backwards: P-type has more holes than
| electrons, n-type has more electrons than holes.
|
| https://simple.wikipedia.org/wiki/P-type_semiconductor
| (property 2)
| m-watson wrote:
| I get the snark but this is also Science and their easy to
| digest news release. It is literally a science journal, not a
| product release or even engineering journal. I wouldn't say it
| really fits into the "advancement in the art," or "actual
| products." It is scientific progress in the material science
| world (which I know is your last parenthetical aspect of your
| comment).
| jakedata wrote:
| Even cheaper material converts electricity into heat!
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