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New Material Breaks World Record Turning Heat into Electricity (tuwien.at)
424 points by de6u99er on Dec 31, 2019 | hide | past | favorite | 152 comments

I've always wanted to build a little hobby project where I put TECs on top of my wood stove and have a radiator outside with coolant to get a nice big heat difference (maybe 100C to 200C) across them and make power in winter when solar isn't so great in the Yukon.

I know it won't be a massive amount of power, but given it will be 24/7 for about 6 months of winter when the wood stove runs, I think it will be a useful amount.

Does anyone know where I can buy TECs that will handle extremely high temperatures like this?

All the ones I see say they're rated at about a max temp delta of ~67C-72C

You'd be actively cooling your wood stove by much more than the power you'd extract, and you won't get more than enough to charge a phone or laptop. TECs are just terrible.

You'd get much better result by making a small steam plant with the same setup: boil water on stove, drive plant (turbine or piston), condense outside, repeat.

However, if you really want to do this with TECs, stack them to lower the per-unit temperature differential, or distribute the heat energy over a larger area and run them in parallel.

I’d suggest doing that operation on the outdoor side exhaust where the heat loss would be irrelevant.

I doubt there's enough heat to extract there. Low-pressure exhaust gas is useless, and I don't think a metal chimney exiting out through a wall would conduct enough heat on the outside on its own.

A small stirling engine would be easier and safer than a steam setup.

The good ol' Stirling engine was tried out -- at a few locations in the US Southwest 10 years back -- to generate megawatts of solar-powered electricity (25kW per engine) at the focus of parabolic mirrors.

It got beat out by subsidized Chinese-produced PV panels (SES was forced into bankruptcy).



My senior year project ten years ago was exactly this - solar thermal + a Stirling engine. When we started the project, we estimated it 20% or so cheaper than solar PV. In that one year solar prices halved or so, leaving us at a dead end.

I ended up consulting with leather plant for their hot water needs via solar thermal. At least that is still viable.

Interesting. I just learned about that energy combo, and Stirling also makes a lot of sense for someone with a non-solar heat source!

Amazing how China came along at the time it did. The hardball politics aimed against US solar startups since Carter has been a fascinating tale with little mainstream coverage.

I'd argue that a steam setup is considerably easier and more proven, but a Stirling engine is certainly safer and more efficient.

(A homemade setup would not be very efficient regardless of technology chosen, so I'm ignoring complexities of elaborate high-performance boilers.)

There are some single layer units that can get up to ~90 of delta_T, but I don't think they're worth dealing with. As a sibling comment points out, you can stack TECs - indeed, you can buy integrated units with very high delta_T that are just pre-stacked TECs.

I think it'd certainly be fun to play with. Some bits of warning - most TECs are physically quite fragile. Not in the sense that you need to be super careful when handling them with your hands, but that heat stresses can totally wreck them. Do NOT hard mount both sides (hot and cold) to different materials - the differential thermal expansion on the two sides has a potentially of ripping your TEC apart. You may be able to get away with a hard mount (such as solder) on one surface, and some sort of thermal transfer material on the other.

Also warning, your hot side is hot enough to start doing weird things with normal solders, which might be the bigger limiting factor.

Won't this reduce the thermal output of your stove quite significantly? I suppose that might not be a problem in practice (most wood stoves I've used end up overheating the room if you're not careful), but it's not like it's free energy :P

> Won't this reduce the thermal output of your stove quite significantly

I'm going to chime in and say that I think it will be insignificant. I don't know for sure, but I really doubt you could do much to cool the stove. When it's cold in the Yukon, I'm literally stuffing in ~8-10 big logs every ~12 hours.

It's not at all uncommon for the base of the chimney to be glowing red. Obviously not ideal, but it happens.

When it's past -40, I set my alarm for 1am to get up and put in more wood. The stove would just last the night if I didn't, but it's a pain to light it again from scratch every morning, so it's easier to just keep it going.

All of that is to say the wood stove is absolutely pumping out heat 24x7 from ~September to ~April.

If I already have batteries and charge controllers and inverters, why not wire in a handful of TECs.. even if I only get a combined total of 100W, that's worth having over those months the sun is not up for long, and not strong.

Glowing red?

As an Amateur Blacksmith (and lifetime member of the Blacksmiths Guild of the Potomac), I was taught that color meant you were hitting 500-600 degrees Fahrenheit, which is usually about the lowest temperature you normally want to have when working on a piece of metal.

If you’re hitting those kinds of temperatures, I’d think you would need some substantial work done on the thermo electric components to keep them from melting, much less being able to operate.

Or am I missing something obvious here?

> Even if I only get a combined total of 100W

Quoting Wikipedia:

> The typical efficiency of TEGs is around 5–8%

To get 100W out at 5% efficiency, you'd need to put 2kW in, 1.9kW of which has to be moved away to keep the cold side cold with perfect cooling.

Realistically speaking, the cooling will not be that efficient, and will probably cost you a bit more energy. I'd ballpark that to 2.5kW lost total for 100W of charging.

That's pretty significant.

Thermoelectrics have terrible efficiency, that's why they're hardly used despite the fact that waste heat is literally everywhere. Your computer, your phone, your car engine, everywhere there is energy to be recovered. In theory, any heat-based powerplant could use them, but instead they all boil water and drive steam through turbines, which is much more efficient.

Thermoelectrics you can order from a catalog have real world efficiency ~6%, which is on the order of what a well engineered practical Sterling engine will do for converting heat to electricity without any moving parts to wear out, exotic working fluids/seals, or ... complete lack of supply chain for any of the above. If this new material pans out it could be on the order of 24% efficient, which would be preposterously better than any heat engine you can fit in an Alaska cabin.

I hate the computer programmer weeb meme of suggesting a Sterling engine for every damn thing. None of you jokers suggesting this has ever built a real world heat engine, let alone attempted to engineer an efficient one from scratch, which is what you'd be doing in the case of log cabin Sterling engines. There are excellent reasons they're not commonly used, and less thermodynamically efficient external combustion engines (like steam) are used. The problems with making them work efficiently are immense.

>would be preposterously better than any heat engine you can fit in an Alaska cabin.

Or a cabin on Mars. Solar and nuclear would be used on Mars. For nuclear - with 20% efficiency i think it would allow to use simple RTG (Matt Damon style) instead of full blown nuclear reactor with working fluids, pumps, turbines, etc.

> Thermoelectrics have terrible efficiency

I agree with what you're saying, but the point is that the woodstove is running 24x7 in the winter, and the solar is very pool. Whatever energy I can get from the TECs is an order of magnitude more than I'll be making without them - i.e. zero.

I think you could build a panel of TECs and just set it up near your wood stove. The radient hear from the stove would be enough to keep the TECs at high temp on one side and room temp (maybe with some heatsink) on the other side.

You could adjust the distance from the stove to keep things within operating range.

>> Won't this reduce the thermal output of your stove quite significantly?

Yes. You want to have the "cold" side indoors where the heat is going anyway. You might think it's all going outside in the end, but we dont want to create a new path for it to get there.

BTW a sterling engine running a generator seems like a good idea in this case.

Hello fellow Canadian :)

Wouldn't a home made Sterling Engine be easier and cheaper? Then use the motion to power a small generator.

But like others commented you may just end up cooling your stove. The Yukon can get pretty cool.

Maybe an old washer motor, a prop to generate power from wind? Or solar in the summer when light is ample.

Yeah, I've seen people who use small wind turbines to generate electricity far north. Seems like the best way to do it.

They're very noisy, and you have to get them above the trees, which is quite high. Also where I live is not very windy.

That's interesting. I'm curious about your living situation, though. Do you live out there most of the year (are you there right now?), or is it kind of a vacation home?

Sounds cool... I'm always interested in off-the-grid living arrangements.

I don't have enough money for a vacation home! I'm full time in the Yukon when I'm not on the road.

Many people up North have solar setups and are off grid, usually with older lead-acid battery setups which work just fine.

Solar is great in the summer when the sun is up for 20+ hours a day, but slim in the winter when we only get ~4 hours of sunlight. Most people supplement with a generator for a couple of hours a day which is what I really hope to avoid with ideas like this TEC on the woodstove.

The stove is already pumping out so much heat, and it's so cold outside I feel like the temperature difference is just begging me to do something with it!

My other dream is to by land on moving water (river, stream) and make a little water wheel that turns an old pickup truck alternator. It will be killer in summer, but it's a problem in the winter because the water will be solid for ~5 months.

Are you software/do tech work? Do you work remotely? And are you completely off-grid, or live in a small community? I just find it very interesting.

By the way, I wonder if it's possible to use waste heat from a generator to warm your house, so you can turn down the stove.

(Also, I was curious about your project idea too and it turns out they do already build wood stove thermoelectric generators if you Google that term...)

That's a cool idea.

I came across this link because I want to build cheap small sensor stations using LoRa to transmit data (gps location?, temp, humidity, air quality) to a central server.

Solar is not really an option because it needs to be cleaned once in a while.

how big of a temperature difference do thermoelectric materials usually require? is it like dozens or hundreds of degrees over a given period, or something that's likely to be encountered in a normal environment?

Typical applications span the order of tens of degrees Celsius.

Tear one of these apart? https://www.amazon.com/dp/B007BLN652/ref=cm_sw_r_cp_api_i_5j...

You could also use the coolant to pull heat off the stove (obvs with appropriate safety built in) and run the hot side of the TEC within spec.

I’ve seen wood stoves get red hot after an incorrect damper setting runs for 5-10 mins, direct heating might fry your circuits.

I've been experimenting with this idea too. The idea is to drive a fan, which blows on metal heatsink attached on the cool side of the TEC. The air stream further accelerates the fire, so this becomes a reinforcing circle. Directly wiring it is not enough, you need a battery to start, buffer, then you need a controllers, never had time for this

There is a company making beautiful camping stoves with TECs and fans: www.bioliteenergy.com

How much power are you trying to make? You can already buy "off the shelf" USB power supplies for camp fires

As much as possible. I would probably cover the entire top of the stove in TECs (so maybe something like 0.5m^2). If I wanted to I could play with adding some to the sides, onto the chimney, etc.

Essentially, it's just to supplement the solar which as I said isn't so crash hot in the Yukon in winter. It's a hobby, and I'd like to see what I can get out of it.

Again, because it's 24x7 for ~6 months I think it might be a fun side project to play with and watch what I can get out of it.

> How much power are you trying to make?

> As much as possible.

That is not a useful response. Would it be worth doing if "possible" turned out to be 0.1 mW? 1 mW? 10 mW? 100 mW? 1 W? 10 W? 100 W? 1 kW? 10 kW? Presumably somewhere in that sequence your answer goes from "no" to yes" and that point determines what tradeoffs you're going to be willing to accept in order to increase your power capacity.

People have suggested steam engines. Those would definitely produce more power than TECs, at least twice as much and potentially six times as much. But they are far more likely to kill you. Is that tradeoff worth it to you?

TECs are pretty expensive per watt. Are you really willing to spend tens of thousands of dollars if it will increase your energy output a little? How about hundreds of thousands?

There are tradeoffs in any engineering design. It's obvious that more power is better, but without some idea of the shape of your utility curve, it's impossible to evaluate those tradeoffs in a useful way.

Co-generate with a Stirling engine or steam turbine. Your application is the wrong scope for TECs. It will be a hundred times more expensive, and a tenth of the efficiency.

Last time I was looking at efficient camp stoves I ran into this guy:


The idea of putting my phone, or any lithium battery really, that close to fire... this plan is not for me.

Couldn't you get around that with a really long USB-A-to-whatever charger cable?

Slapping a Stirling engine on a rocket stove just seems like a really good idea to me. My major concern would be the in-backpack weight and volume.

DC doesn’t like long runs, but I believe there’s a battery in that yellow block along with the charge circuitry. If I’m wrong it may warrant another look.

Could you chain 3 of them using a tank of coolant at room temp as the between value. Or make it water and put the TEC on the cold side of the tank

The plan is to have a tank of glycol coolant sitting outside (at around -20C to -40C ambient) and mount a radiator outside. I'll use a fish tank pump or similar to circulate the coolant. Put water cooling blocks onto the TECs so the wood stove heats one side to around 100C to 200C, and the cold coolant coming in brings it back down, to hopefully get a temperature difference in the range of 100C (ish).

It's all just an idea right now, first I have to find TECs that are up to the heat directly touching the stove.

You could use the waste heat that goes up the chimney to warm the fluid with something like an automotive intercooler and set the system up backwards, maybe?

Ohhh, I hadn't thought of that idea. Interesting. I will be sure to experiment with that!

If you cool the exhaust gases too much they will condense in the flu, and the condensation is incredibly corrosive. Stoves/furnaces etc. (except for condensing ones) intentionally waste a lot of heat intentionally keeping the exhaust gases hot just to prevent this.

The hot exhaust also helps create airflow that moves the combustion products out of your living space.

It would be neat to recover otherwise totally wasted heat, just be careful.

Solar & lithium batteries are so cheap from scale, it's worth comparing the cost, even though production is very low in winter.

Don't get me wrong, I'll still have a good deal of solar. I just want to supplement it in the winter, especially the ~20 hours a day when the sun is below the horizon!

Every time some phenomenon arises from a recipe of fairly typical materials I wonder what other surprises nature has in store for us.

The idea that the crystalline structure plays a large role in the bulk thermal conductivity of the material is kind of mind-blowing at first and then retrospectively obvious.

I am twenty years removed from it, but I used to be well-informed on this kind of thing; I have a PhD in mineral physics.

Let's see how well I can explain this (haven't read the article, yet, sorry! Waiting for a plane...)

So you're no doubt familiar with the physics of a vibrating string; it resonates at wavelengths (length of string, 2 * length of string, 3 * length of string... n as n->inf). So you can express any vibrational state of the string as sum(intensity * wavelength); so you can represent the state of the string as a vector of intensities on a basis of allowable vibrations of the string.

Let's call these _vibrational modes_. Let's assume occupancy of these modes is quantized. It's (sort of...) the same as energy levels of atomic orbitals in electronic structure, if you remember that from chemistry classes; the way it's not the same is important (bosons vs fermions) but not at this level of handwaving :-)

So this is how solids store energy, and we call this energy "heat".

A reasonable approximation for a crystalline structure is balls – point masses – connected by springs, where the springs are covalent bonds, plus electrostatic effects between point charges. Intuitively, you can follow that the same kind of _vibrational spectrum_ will arise from this arrangement (in the same kind of way; the solutions of the differential equation of this system of forces under periodic boundary conditions). So materials have resonant frequencies in the same way guitar strings do.

Therefore, this vibrational spectrum defines the thermal behavior of a material; heat capacity, thermal conductance, etc etc etc etc. Each of these vibrational modes is also tied to a collective motion of the particles in the material, which (if sufficiently violent) will tear the structure apart – there's the solid-to-liquid phase transition – or, more subtly, if lost will lower the symmetry of the crystal structure, which gives rise to solid-to-solid phase transitions (an example would be alpha to beta quartz, which will crack your crockery if you leave it in the oven on a cleaning cycle; https://en.wikipedia.org/wiki/Quartz_inversion).

There's a lot of depth here, as you can imagine!

I think you meant to say length of string, length of string / 2, length of string / 3, ...


Indeed I did! Thank you. (This is what happens when you write in a hurry.)

Hope you had a nice flight. Happy new year.

One leg down, the long one to go...

This reminds me of this Sixty Symbols video which explains why light is slower in media such as glass than in a vacuum:


The incoming light wave causes an avalanche of secondary waves through electromagnetically perturbing the individual atoms, and the superposition of all these results in a wave that seems to travel slower than the speed of light.

> A reasonable approximation for a crystalline structure is balls – point masses – connected by springs, where the springs are covalent bonds, plus electrostatic effects between point charges.

Thanks! This is a great analogy.

This is the model used by most chemical simulation codes (that don't account for quantum chemistry). See for example the LAMMPS simulation software (https://lammps.sandia.gov/)

If anything I wrote has been original, it would have been a big red flag :-)

This is so cool, thank you. I dabble informally and quite primitively with signal processing, so the idea of vibrational spectrums in a crystalline structure really resonates (hurrr). Now i have a whole new set of mental imagery to process when i pick up the pan with a handle that had the handle a little too close to the flame. Thanks!!

I hate to mess with your physics education but silicone covers for all your metal pan handles is a godsend, even for atheists.

Great information!

Also, (and I may be totally wrong about this!), the concept of Annealing from metallurgy -- seems related to that of Quartz Inversion:


Well, both annealing and dunting ("quartz inversion") have to do with the crystalline structure of materials, but that's where the similarity ends. There are many important crystalline phase transitions in metallurgy that are more similar to dunting; the most important of many examples is probably the ferrite-to-austenite transition in steels at 700–1400°. But annealing is not such a crystalline phase transition.

Well written I must say. Makes me very curious about crystals and material physics (especially since I got interested in low level electronics and semi conductors).

Any suggestion to read ?

Not really light reading, but any good solid-state physics textbook would cover most of this. I learned from https://www.amazon.co.uk/Introduction-Mineral-Sciences-Andre..., which is quite a bit more explicitly mineral-sciences focussed.

Aight, I'll see if I can digest it.

The space of "fairly typical materials" is very wide because there are lots of elements and their combinations blow up very fast. Secondly, materials are often very sensitive to small physical or chemical changes, resulting in wildly differing properties.

To you the simpleness of the final result is surprising, but that simple result was discovered after a long and exhaustive search. A search into a wide and shallow space can be just as impressive and difficult as a search into a narrow and deep space.

I think OP was just expressing delight and wonder at our surprising and elegant universe rather than making light of the findings.

Actually looking into independent power sources for small IoT sensor stations for a hobby project. I think to understand climate change better, we need more data.

Engineer here btw.

Yep! Delight is a great word for it.

It goes even beyond the combinations, no? The physical manifestation of the end material plays a key role in its properties, so you could just make a simple alloy of the above and not have this thermoelectric effect. Only when you apply them just so do you get this outcome. So crazy...

> a recipe of fairly typical materials

We don’t have good theory for materials science. Our understanding is closer to a list of observations (“effects”) than anything unifying. That almost ensures there will be surprises in the gaps.

At the same time, popular disillusionment with repeated claims of wonder materials has led to—in my opinion—underinvestment in basic research.

Just to clarify why these aren't used everywhere: heat-to-power devices act as insulation (compared to just letting the heat escape). If you have something that you're trying to keep cool, like a CPU, a system that shunts heat straight to the surroundings will always give better cooling than a system that puts layers in between. Contrariwise, if you have a need for electricity, mechanical heat engines will almost always be more efficient. Solid-state heat-to-power only makes sense in a narrow set of cases which aren't suitable for direct cooling or heat engines.

But there are some pretty cool applications. Apparently the heat difference between a buried water-pipe and the surrounding earth is already enough to power a wireless sensor, which can transmit data to localize leaks, for example.

Voyager 2 and 1 are powered by thermocouples and a chunk of plutonium.

(I ordered them that way because Voyager 2 was launched first)

What does the level of performance indicated here likely mean in terms of the efficiency of, say, a thermal energy plant of some description? How far is the needle shifted for an end user?

From mucking about with the device efficiency formula from wiki (https://en.wikipedia.org/wiki/Thermoelectric_materials#Therm...), and a change of zT from 2.5 to 5, we see a maximal possible efficiency increase of 38% (when T_c == T_h).

Wiki also tells me that the best TEG modules currently lock in around 8%, so we're looking at like 10-11% at best with the new material.

So from a bulk scale electricity standpoint... the needle probably hasn't shifted at all. From a small scale? In the IoT like applications (as mentioned in the press release), that extra 30-40% is nothing to sneeze at.

Also, this seems to suffer the same problem that most high-zT thermoelectric materials do: the total power handling capability is too low to be worthwhile. From a large-scale waste heat recovery standpoint, you're probably better off with a less efficient solution that can actually handle a useful proportion of your total heat output.

You have some kind of error here: with T_c = T_h, not only does Wikipedia’s formula give 0% efficiency, but it must: any power at all generated with no temperature difference would make a perpetual motion machine.

Sorry, I was ignoring the left side (the T_h - T_c / T_h) part of the formula to see the relative change from changing zT from 2.5 to 5.0. Effectively I was looking at the relative efficiency of the high zT material in the limit as T_h approaches T_c. Which as you point out, drives the real individual efficiencies to zero. I was just trying to get the "best case" scenario.

Would also point out that for the IoT like applications, the assumption of T_c ~= T_h isn't so bad. For example, if you wanted something powered off residual body heat, you're looking at something like 293/310 = 0.945. For

For T_c=293 and T_h=303, you get efficiency = 1.4% for zT=5 and efficiency = 1.0% for zT=2.5. So about a 40% relative increase as OP calculated and negligible absolute change.

Improving from 1% to 1.4% is a huge improvement. It’s 40% more cooling for a given power input or 40% more power output for a given amount of heat consumed. Alternatively, it means you consume only 1/1.4 the resources to achieve your goal.

This does not imply that 1.4% efficiency is enough to be useful for most applications, of course.

The Peltier and Seebeck effects are so grossly inefficient that even an order of magnitude increase in efficiency doesn’t bring it into reason for basically any purpose. I’m not actually aware of any device ever made that uses the seebeck effect in any substantial way other than the little heat powered fans people put on wood stoves.

The peltier effect is just down right awesome, you put power in and now it’s cold!? Reality steps in at some point when you need to drive down the efficiency even further to get large differentials and ugh. They’re insane to deal with, any amount of thermal load worth speaking of means you have to use a phase change system.

It is very handy for camera sensors though and other scientific gear. There’s a world world of CCD sensors that act in a vacuum with peltier devices driving them below -30c to reduce the noise produced by the sensor.

> I’m not actually aware of any device ever made that uses the seebeck effect in any substantial way other than the little heat powered fans people put on wood stoves.

It's used to power space probes that can't use solar panels. https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_ge...

My camp cooler is powered by a 60W peltier. Plugs in to any automotive cigarette lighter. It will keep things refrigerator cold for as long as you want, and it's almost completely silent in operation. There's tons of different models on the market. FWIW.

You realise how inefficient they are when you load it full of warm beer and run it for a few days and the beer isn't even cool yet. From that 60 watts of input power, you only get ~4 watts of cooling, and with some leaking through the walls of the box, the time to cool down something of substantial mass can be weeks.

That's why you have to use a real fridge to do the work before starting the journey. And at that point, those electric fridges are only slightly more useful than a pile of ice packs.

A couple of watts of cooling is not even enough to overwhelm checking on the beer frankly. All peltier elements are effectively the same efficiency: atrocious.

Obviously, using pre-cooled drinks is better, but if I put in a 12 pack of some beverage, it will be fridge-cold within 24 hours. In practice, it's never been an issue.

>It will keep things refrigerator cold for as long as you want, and it's almost completely silent in operation.

that's more a function of the insulation , rather than the cooling ability. The wattage needed for 'thermal maintenance' is far lower than needed for actually removing heat from the system.

Peltiers' are kind of on the same scale of efficiency as using your car (on purpose) to cook food in the engine bay.

...and yet that is still useful enough to be the right answer for some products. For the camp cooler example, it means I don't have to waste precious space on ice packs, nor worry about water as ice melts. If I put in room temperature sodas, they will be cold within 24 hours, which is good enough to be useful. On cold days I can run it in reverse and have a hot drink at break time. And the cooler/heater itself barely adds any weight to the cooler itself.

As a side note, look up the book 'manifold destiny'. It's all about cooking with one's engine bay. An amusing read!

it works similar to a thermocouple. A normal thermocouple needs a voltage bridge to increase the voltage with a millions to get anything that can be read by a digital 5v meter. These materials don’t need that. And a couple of degrees could produce a workable voltage. But the title Of the article states that the material is meta stable, unsure if that means it will work for a couple of seconds then die. Also, vanadium is used which makes it quite costly.

The predominant use cases for this will be powering ultra-low power sensors. The higher power could enable better (longer range, higher bandwidth) radios in the sensors.

This would be an even bigger deal for remote spacecraft that rely on the heat from on-board nuclear reactors.

I think you are thinking about an RTG instead of an actual reactor.

Some space craft have actually had full reactors on them believe it or not.

There were indeed real nuclear reactors with thermoelectrics being launched in the cold war.

However, thermoelectrics have an efficiency well below 10% (maybe a bit better with this improvement but not much). For that reason, future reactors in space will likely use Stirling engines instead.

Correct. Space stirling designs* (and tested engines) have been much more performant than the RTG designs

*I spent part of my career working on these devices and saw many of them running in labs

Checks out - I didn't realize we actually did fission... in... spaaaaace!


Unlikely. Much easier to just connect the sensor to the main power supply via a wire.

RTGs[0] use the thermoelectric effect to generate electricity from the decay heat of radioactive isotopes. This new material would allow better power generation using RTGs.

[0]: https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_ge...

Could this also be used to reverse electricity into cold-heat gradient with high efficiency?

Yes, the thermal-electric effect is reversible. It's sometimes called the Peltier effect (or thermal-electric cooling) when used in heat pumping mode, and Seebeck effect when used in electricity generation (thermal-electric generation).

If you have a very small cooling job, yes. Anything above a handful of thermal watts is still better off using a compressor.

We were talking just the other day about back-side power distribution in ICs. Basically you bury the power rails really deep, lap the chip down to half a micrometer, and add through vias to ge to the rails.

So now you’ve got a very thin chip and all the power comes in on the side with pretty much nothing else on it. I wonder if you mount the chip backside up, put these little peltier devices on the hot spots, if you can maintain a higher heat transfer rate.

The thing is, a chip generally cools just fine with heat pipes and fins up to 200 or more watts. And the built-in heat spreader gets rid of hot spots very effectively. At that power level a peltier tends to be worse than useless, even if you're putting enormous amounts of power through it. Even if you double the efficiency it's still a bad option.

Overclocked threadrippers can hit 500W[1]. I can see peltiers and 'vapochill' style phase-change cooling making a comeback...

1. https://www.anandtech.com/show/13124/the-amd-threadripper-29...

I think I accept the argument that in a desktop with a giant cooler attached to the CPU, this may not improve things or make them worse.

But there are an awful lot of mobile processors with passive cooling or complex heat pipes, and it would take more convincing that such a scheme would also fail there.

I'm also wondering if it might be useful for 'race to idle' situations by extending the time until thermal throttling kicks in.

Phase change yes. Or water chillers.

I can't imagine why anyone would be more inclined to use a peltier as wattage increases. Higher wattages make that idea progressively worse unless you have some very specific and strange requirements.

Are you talking about the giant Peltiers that flopped in the late 90's and early 00's? Nobody is talking about that. I'm talking about micron, maybe millimeter-scale peltiers to increase the thermal conductivity of the absolute worst spots on the chip. That may mean a particular ALU, or it could mean circuits with far more layers than we can manage now (due to yields and thermal limitations)

> the absolute worst spots on the chip. That may mean a particular ALU

The worst spots aren't much worse than the median spots (over calculating silicon, not cache). Anything big enough to be a hot spot, like a big ALU, is big enough to represent a large portion of your power budget. The main goal is to get all the heat away from the chip, and putting peltiers on a large portion of the chip gives you more heat to take away. For anything significantly smaller than that, the heat bleeds out without the need of a peltier. There might be a middle ground where peltiers could make a real life difference, but I'm skeptical.

> or it could mean circuits with far more layers than we can manage now

That sounds like you're cooling the entire chip, which is the worst time to use a peltier.

Until now... maybe.

Yes, the thermoelectric effect works both ways.

If an advanced civilization continued to improve the efficiency of this effect would they eventually use it to capture the majority of the energy output of their local star? You could have a shell of high efficiency solar satellites surrounded by another shell of high efficiency Seebeck satellites. What would this look like from a distance? Would they be able to capture enough energy so their star would be indistinguishable from the ambient temperature of space?

Our galaxy and others appear to be missing most of the mass i.e. stars that they should have in order to rotate as fast as they do. We put the figure for missing mass at about 80 to 90 percent for our galaxy. What if our galaxy and others are already colonized by advanced civilizations that make maximal use of the power output of stars so it simply looks like we're missing most of the matter that should exist. This could explain why there is a variation in the amount of missing mass between galaxies with some galaxies apparently containing 0% 'dark matter'. No advanced civilization = no dark matter, different amounts = different stages in development of the galactic civilization.

Could this be a solution to the Fermi paradox?

> Would they be able to capture enough energy so their star would be indistinguishable from the ambient temperature of space?

You would still see infrared:


> Such a feat of astroengineering would drastically alter the observed spectrum of the star involved, changing it at least partly from the normal emission lines of a natural stellar atmosphere to those of black-body radiation, probably with a peak in the infrared.


> A Dyson sphere, constructed by life forms dwelling in proximity to a Sun-like star, would cause an increase in the amount of infrared radiation in the star system's emitted spectrum. Hence, Freeman Dyson selected the title "Search for Artificial Stellar Sources of Infrared Radiation" for his 1960 paper on the subject.[4] SETI has adopted these assumptions in its search, looking for such "infrared heavy" spectra from solar analogs. From 2005, Fermilab has conducted an ongoing survey for such spectra, analyzing data from the Infrared Astronomical Satellite.[5][6]

Only if the 2nd law of thermodynamics holds. When speculating about advanced civilizations building Dyson spheres, why not speculate about the bedrock of science as well?

There are (probably) other paths to avoiding this conundrum as well. Spitballing here, but perhaps the 'satellites' in this case can be pairs of orbiting black holes which emit the waste heat in a band we don't detect (gravitational waves).

I always forget about the concept of gravitational engineering, probably because it's just a bit scary to think about the unknowns involved. If you could mass produce small black holes and position them you could pretty easily construct giant lenses capable of redirecting the output of a star to anywhere you please. That's more than a little terrifying.

> Only if the 2nd law of thermodynamics holds. When speculating about advanced civilizations building Dyson spheres, why not speculate about the bedrock of science as well?

If the person I replied to qualified their comment with "lets assume laws of physicis is not relevant" then sure...

Except when discussing technologically hyper advanced civilizations, the 2nd law of thermodynamics is a (vaguely) reasonable place to expect our laws to break.

The 2nd law is an observed fact with very shaky theoretical underpinnings (I am not talking about the behavior which has very strong underpinnings). It appears to be an emergent behavior rather than a fundamental one. It is a surprising fact given what else we know about the universe. It breaks the time symmetry of the other laws of physics. This is akin to learning that even though the laws of physics dont break position and rotational symmetries, there is a preferred direction and spin. In fact there is a preferred spin- all neutrinos are left handed. There are huge research efforts to understand why or if there are corresponding right handed particles. Broken symmetries mean big things because as far as we can tell the universe is ruled by what symmetries exist and in what ways they are broken.

You're ignoring the point I was making about capturing the infrared waste heat. It seems counterintuitive for a civilization to go to the effort of encasing their star in a shell of satellites while dumping energy as waste heat. Surely there must be some way of utilizing that energy and my conjecture was that advances in the efficiency of the Seebeck effect might lead to a way to fully utilize that waste.

If we look at our planet, we should realize that fossils and nuclear power are limited. Aside of the quantitative limitation, we get to feel the negative green-house effects now, making alternative energy sources even more urgent. The only real long-term source is the sun. We HAVE to (completely) switch to sun energy within the next 100 years. This will require huge photon harvesting facilities. For now, covering our deserts would be enough. But what if our energy requirement increases 10 fold? The more energy we have, the more people can have steaks and luxury. In the SECOND we reach the point of energy limitation on Earth, we will expand our photon harvesting facilities into space, close to Earth. This will grow with generations, so will technology. The gigantic amount of energy daily shining onto Earth is still ridicously few compared to what the Sun radiates every second. The photon harvesting layer will shrink, become more efficient, harvest more wavelengths (maybe even just a single atomic layer) and routed to central cores where it is collected and sent to Earth or the future intelligence habitat. Even if it is just a mirror, redirecting the photons to a central core, which routes it close to Earth, where it will evaporate water - or whatever much smarter ideas our future generations will find.

And this is what we could do now with our technology.

The infra-red issue, imho, is based on current technology level. No light enters the depth of the ocean because life evolved to build photon-recepters of all wave-lengths, even the less fruitful.

Taking this into consideration, every maturing civilization WILL inevitably produce Dyson spheres at least transiently. We already started it! Just look at the solar moduls of the ISS, which are actually the beginning of a Dyson sphere.

What would they use all that energy for, and how would they use it in a way that wouldn't radiate heat or light on par with the amount captured?

A good use might be computing power whether its for storing the minds of everyone in the civilization or powering one big mind or simulating universes or maybe it's all dedicated to finding a way to reverse entropy.

If we're assuming a highly advanced civilization aiming for maximal efficiency I would hope that they have figured out how to make all of their electrical systems out of high temperature superconductors.

Is there really a way to "use" energy for computation that doesn't just convert all of it to heat?

Store it as mass!

Sounds like a good beginning to a collaboration novel by Neal Stephenson and Alastair Reynolds.

They kept referring to IoT uses in the article. It got me wondering if the best usage of this would be to be embedded in a jacket’s outer shell. You get the surface area but not a lot of wattage of heat, I guess. But it sounds like it makes a pretty good insulator. I could certainly imagine sensors running off that kind of power.

Something I was curious about, but not sure where to start - suppose you wanted to make something that at 400-500K, would emit radio waves from which the temperature could be derived. And as small, simple and durable as possible, so it didn't break down.

I mean, there's going to inherently be infrared, so how can you convert that to radio of roughly a desired frequency range without complex machinery?

Does anyone know if this discovery can be used to boost the efficiency of solar panels? Don't solar panels get incredibly hot?

You can use these types of materials to extract energy from any energy gradient.

In the particular case of solar panels, in order to have a workable thermal gradient, you need to have some sort of conductive path from the solar panel to the cold reservoir (assume the ground under it) - that's extra cost there. Then once you have the TEG running, what you're actually doing is adding an impediment to heat flowing from the solar panel to the cold spot, likely causing the solar panel to be a bit warmer (thus decreasing its efficiency). The increase in energy production per given investment is almost always going to be lower than just getting more solar panels.

You see this is most bulk energy production contexts. It's rare for these energy scavenging techniques to make economic sense. Where you start seeing them make sense is when you have other constraints come into play. You can see this with other aspects of solar generation like solar tracking.

The title is misleading, the technology (thermoelectric cooler) does not turn heat into electricity, but temperature gradients.

It needs a nearby source of cool to work, and when a solar panel is hot, oftentimes everything surrounding it is hot.

My intuition says the shaded ground below it can be quite a bit colder.

I have no real data...

Sadly the key here is lab scale and vanadium. Costs won’t make it worthwhile.

Commercial vanadium metal, of about 95% purity, costs about $20/lb. This is a tiny layer, so even at the 99.9% purity level cost of $100/oz, materials cost is not likely be a critical factor. The main constraint is that it's not making much power -- at this level it's really for very low power applications, especially things like sensors and comms.

I don't think the research is intended for large scale electricity production. It's for small sensors and processors and that won't cost much.

This opens up a quiet a few possibilities like buy a temperature sensor place it somewhere and it starts feeding data into your home WiFi. No wires, no batteries.

Easy, just build a fusion reactor capable of eventually producing vanadium from hydrogen, and you got yourself a stew going!

Edit : Method of producing said reactor left as an exercise for the reader.

Vanadium is only $6 per pound. About as expensive as street price of ice cream. It's not a rare earth element or anything like that.

Lots of hand tools like hex-head wrenches also use it. Typically they get stamped with "CR-V" for chromium-vanadium. It's basically all you need to know when buying standard quality hand tools.

In addition to being affordable the material is available in bulk and there exists an industry which knows how to work with it. Same with all the materials mentioned.

I'm glad you ran the numbers for this to reach such an important conclusion about the future of this technology, RandomWorker. Care to show your working?

does this imply an overall entropy reduction for a whole system comprising a device and support apparatus for reusing its heat as energy source supply?

No you can't make a perpetual motion machine with it ;)

But could you produce a cooling system that this could power?

Or at least recycle some of the heat fridge/freezers produce back into electricity.

>Or at least recycle some of the heat fridge/freezers produce back into electricity

This was already possible. Now you could just do it more efficiently.

I was thinking more like CPUs and GPUs

Right. I'm thinking about server farms.

i am aware of it. i was not pretending we could reach zero entropy but nevertheless it manifests entropy reduction compared to an energetic non-optimal raw material doesn't it? meaning if we need less energy for the same amount of work we do it more efficiently and therefore require less (but not null!) entropic output

Are you asking if it violates the 2nd law? Of course not.

It's just a heat engine like any other electrical generator so it's not going to have fundamentally new kinds of applications.

Don't forget you can also use the waste heat from a device (like a computer) to run a mechanical heat engine to generate power to help run the device. But only partially. I guess we don't do that much because it's probably not economically feasible. That's kind of what turbochargers in cars do though.

Would this be efficient in a mobile phone?

This will be slowly but surely be used everywhere. Reducing heat output while providing electricity is almost always a win-win situation.

There are a lot of factors you're not considering. Reducing heat output is good, yes, but putting a layer between your chips and their heat sink is bad! Even though the total heat output is lower, the chip temperature will be higher, because it will be more insulated. There is no way around this; any heat-to-power device acts as insulation compared to a plain heat conductor. You will also have added weight and cost. In a phone, where the heat differences are small, the electricity gained will be almost nothing. So actually we're not likely to see this in phones.

This adds weight and volume that are bad for a mobile phone. Also, the size must be enough to process all the heat from the phone. In systems with a big heatsink you will need a bigger device between the heat source and the heatsink. This will not be a problem for phones, but it may be a problem for notebooks.

Also, with a difference of 30C (60F) they increased the maximum efficiency from 1% to 4%, but that temperature difference is probably too hot for a phone in your pocket.

It's probably better to have a smaller phone, or to use the additional space/weight in a bigger battery.

// Removed as I'm not a physicist and may be mistaken.

I think it's correct. Heat is the flow of thermal energy. A portion of that flowing energy is converted to electrical energy. Perhaps you're confusing heat with thermal energy?

There must be some heat flowing to generate electrical power because of the 1st law, so even if the effect is described as being due to a temperature difference, in practice, you also need a heat flow to be useful.

Your quote about "without any side effect" means without heating up a cold reservoir. But the article doesn't claim that.

Heat is the energy, not the flow. That flow is flux or power. A temperature difference is how we perceive or measure a difference in thermal energy density between two places, and is the potential that drives heat flux. A thermoelectric barrier between those two wells can extract energy from that flow, within thermodynamic limits.

Yes, I was a bit sloppy. It's the flowing energy, not the flow of energy. The point of my comment was to distinguish heat from stored thermal energy so the distinction isn't so important in that context.

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