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Cheap material converts heat to electricity

sciencemag.org

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Re: Cheap material converts heat to electricity

#11

Post by [deleted] »

wiredfool wrote: post #7
yetihehe wrote: post #5

Earlier quoted context omitted.

> 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 uni…

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.

[deleted]

Re: Cheap material converts heat to electricity

#12

Post by yetihehe »

kwhitefoot wrote: post #6

> 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.

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.

Re: Cheap material converts heat to electricity

#13

Post by marksbrown »

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!

Re: Cheap material converts heat to electricity

#15

Post by grishka »

calgoo wrote: post #3

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.

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.

Re: Cheap material converts heat to electricity

#16

Post by lizknope »

kwhitefoot wrote: post #6

> 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.

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

Re: Cheap material converts heat to electricity

#17

Post by londons_explore »

lizknope wrote: post #16
kwhitefoot wrote: post #6

> 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.

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

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.

Re: Cheap material converts heat to electricity

#18

Post by JoBrad »

pjc50 wrote: post #9

> 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…

> 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.

Re: Cheap material converts heat to electricity

#19

Post by enkid »

kwhitefoot wrote: post #6

> 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.

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.
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