Cheap material converts heat to electricity

https://www.sciencemag.org/news/2021/08/cheap-material-converts-heat-electricity

by rbanffy • 5 years ago

142 91 5 years ago

calgoo• 5 years ago

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.

yetihehe5• 5 years ago

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.

wiredfool2• 5 years ago

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.

grishka4• 5 years ago

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.

wiredfool2• 5 years ago

Thermodynamics -- you can't win, you can't break even, and you can't even leave the game.

blueblisters2• 5 years ago

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?

France_is_bacon• 5 years ago

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• 5 years ago

Must have been a Pentium 4.

guidopallemans• 5 years ago

Time to air-con the world, I guess

kwhitefoot2• 5 years ago

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.

NohatCoder• 5 years ago

That is because the 90% is heat efficiency, this is for extracting electricity, which is much harder.

IanCal• 5 years ago

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%.

yetihehe5• 5 years ago

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.

lizknope• 5 years ago

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• 5 years ago

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.

enkid• 5 years ago

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• 5 years ago

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.

makomk• 5 years ago

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.

marktangotango• 5 years ago

Isn't the minimum exhaust temperature the same as the temperature of the heated water? How can it be less?

dhajzhz• 5 years ago

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.

namibj• 5 years ago

intake air preheating and cold return water preheating come to mind

pjc50• 5 years ago

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• 5 years ago

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• 5 years ago

So write the paper after that's all done.

m-watson• 5 years ago

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).

robbedpeter2• 5 years ago

Isn't graphene a high quality p type material as well?

What makes a material p or n?

robbedpeter2• 5 years ago

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?

marksbrown• 5 years ago

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• 5 years ago

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• 5 years ago

Why wouldn't airgapped bearings be used for this? Is it too heavy?

darksaints• 5 years ago

Consequently, NASA is often at the forefront of technologies that reduce moving parts. For example:

https://technology.nasa.gov/patent/LEW-TOPS-80

https://technology.nasa.gov/patent/LEW-TOPS-106

Tepix• 5 years ago

How much of a temperature differential is needed? Could this be used on a boat to take advantage of cool water and warmer air?

988747• 5 years ago

Finally! Now we can have an air conditioner that does not require a pipe to blow the hot air outside. Like truly mobile unit.

vlmutolo• 5 years ago

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• 5 years ago

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• 5 years ago

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

layoutIfNeeded3• 5 years ago

That’s thermodynamically impossible.

flavius29663• 5 years ago

Why? You could theoretically take out energy from the room in the form of electricity

jkgktnrnfnf• 5 years ago

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...

matheusmoreira2• 5 years ago

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• 5 years ago

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• 5 years ago

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.

yetihehe5• 5 years ago

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• 5 years ago

There have been stories of people heating houses that way, actually.

matheusmoreira2• 5 years ago

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?

layoutIfNeeded3• 5 years ago

Nitpick: you can’t convert heat to electricity. You need a heat differential.

srean• 5 years ago

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.

jakedata• 5 years ago

Even cheaper material converts electricity into heat!

cblconfederate• 5 years ago

I know a very cheap material that can also be used to convert heat differentials to electricity , called wind

pcdoodle• 5 years ago

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"

SigmundA2• 5 years ago

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.

mrfusion3• 5 years ago

Could you put these on the backs of solar panels to capture some waste heat?

Or tack them on ice engines.

mrfusion3• 5 years ago

You could also built completely silent refrigerators and freezers that last 100 years.

gpm2• 5 years ago

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.

tdeck• 5 years ago

How does this differ from using a Peltier module (already used in some mini fridges)?

billpg4• 5 years ago

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• 5 years ago

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?

bernulli3• 5 years ago

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.

Ajedi32• 5 years ago

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.

billpg4• 5 years ago

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!

oehpr• 5 years ago

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• 5 years ago

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.

grishka4• 5 years ago

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.

grishka4• 5 years ago

Or you could have a battery and store that energy to supply your house with electricity, thus reducing your bills.

billpg4• 5 years ago

That would be useful energy, which thermodynamics says is impossible to extract from heat.

Meandering• 5 years ago

Heat is call "Low Quality" energy in thermodynamics. Heat is basically disorganized particle movement. It is very hard to convert disorganized energy to organized energy like electrical current.

xyzzy21• 5 years ago

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.

Cheap material converts heat to electricity

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