
High-power thermoelectric generator utilises thermal difference of only 5°C - rbanffy
http://www.newelectronics.co.uk/electronics-news/high-power-thermoelectric-generator-utilises-thermal-difference-of-only-5c/175937/
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theothermkn
The Carnot efficiency of a heat engine is 1 - T_low/T_high. When operating
between 305K and 300K (room temperature(ish)), for example, this is 1 -
300/305, or about 1.6%. In other words, the absolute most amount of energy a
device operating over a 5 K temperature difference at room temperature is
pretty dismal. Just because their band gap (for lack of a better term) is
small does not make this device "useful."

For all stories about heat engines running between smaller temperature
differences, the _smaller_ the temperature difference, the _less_ excited you
should be. For example, I have a device that reaches the Carnot efficiency
across temperature gaps of 0K! HINT: It's a rock. Or a paper clip. Or a wet
tissue. Or...

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mrfusion
It could still be really useful for remote sensors and who knows what else. A
lot of places a little power is all you need.

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JackFr
Yeah -- interstellar space, we're talking 67.5% Carnot efficiency.

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foota
I don't think heat engines would work in space generally due to the low mass
of stuff around you that can absorb heat.

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Baeocystin
They work great as long as you have a source of heat and a good radiator. You
don't need mass as a heat sink.

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foota
Interesting, I wasn't thinking about that. Thanks

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theothermkn
At a practical level, your initial instinct was right. In space, nobody can
feel you convect. Essentially all of the waste heat has to be disposed of via
radiation, and this is orders of magnitude less effective than convection at
the temperatures that any known material can withstand. Worse, you don't have
to radiate "just" the waste heat. Eventually, all of your electric energy
becomes heat, too. In other words, _all_ of the energy you extract from your
decay source _will_ end up as heat that you have to get rid of via radiation.
(Well, you could wind a giant spring, I suppose. But, a spring that large
would be a better radiator than energy storage device.)

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Baeocystin
All that being said (and true!), you also have a very cold sink to reject
waste heat to, whether you want to or not. The end result is that heating is
as much an issue as cooling. Thus spacecraft usually wind up with blankets and
radiators, both. :)

Here's a detailed look at the thermal control system for the ISS, for the
curious:
[https://www.nasa.gov/pdf/473486main_iss_atcs_overview.pdf](https://www.nasa.gov/pdf/473486main_iss_atcs_overview.pdf)

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ryanmercer
Can anyone explain the importance of this to someone with no understanding of
physics?

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someonenice
As I see it, this is good for low power iOT devices that are installed in
remote / hard to reach areas (say underground etc. ..). A small temperature
difference could produce power enough to run the device without any battery.

Heart Pacemaker require around 10uWatt and this new power source seems to
provide 12uWatt for 1 cm2. If temperature difference could be maintained, then
could provide a low weight, low power source that do not require changing
battery.

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windows_tips
Is there a 5C difference anywhere in the body? Skin temperature to blood
temperature, maybe?

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function_seven
That's what I was thinking. 37°C inside vs. up to 32°C (90°F) outside and you
still have enough temp gradient to produce the power. All you need to do is
install this heatsink on your chest :)

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crooked-v
And to satisfy precedent, pipe any leftover power after running the pacemaker
to a ring of white LEDs.

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ehead
I didn't see in the article a T_low or T_high where this device was
operational. Normally TEGs work well with high temperature differences
(attached to the side of a hot wire pipe with a heat sink on the opposite
side), and they work poorly at lower temps (room temp). Anyone know what
temperature range this device is made for?

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tgsovlerkhgsel
Misleading title:

> high-power density of 12 microwatts per 1cm2

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IshKebab
That actually is a fairly high power density for this small of a temperature
difference. The main application is probably remote sensors that run on a
milliwatt or less.

Still I agree it sounds misleading.

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abainbridge
The article says:

> shortened the silicon nanowires to 0.25nm

That's a very short wire. Isn't that about the diameter of a silicon atom? I
thought the smallest wires we could make on silicon were about 20nm _wide_.

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swiley
The atoms aren’t that small it’s just difficult/impossible to reliably
manufacture devices with features smaller than that using visible light
photolithography.

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sp332
A silicon atom is about 220 picometers across (subject to change depending on
how you add, subtract, or squeeze the electrons).

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dvh
12 microwatts per 1 cm2

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ddalex
0.12W per sqM

for an intuitive sense, it would take 125 hours to charge a standard phone
with 1 sqM device

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tomtimtall
Or in other words it would be possible to continually power an iPhone with the
temperature difference and area available in a tent. I think the context is
important to whether this is presented as something negilable or something
useful. Though there is absolutely no doubt that we aren’t going to see
extreme amounts of power from this in tiny devices.

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taneq
It also depends hugely on the nature of the generator - if it's a flexible
sheet which can be used to make a tent, then awesome. If it's a rigid sheet
then you'd be far better off making your tent out of solar panels even if they
only saw an hour a day of sunlight.

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tomtimtall
They are not mutually exclusive though. And your tent would tend to have a
higher temperature gradient during the night when there’s no sun.

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MichaelApproved
Could this make radioactive batteries more feasible?

By bringing the temperature differential down, we could use a fairly weak heat
source to charge up a device.

Would we be able to use a tiny amount of shielded radioactive material to
provide a constant heat source and use that heat for the temperature
differential?

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okket
12 uW per cm2 is still poor, you'd need gigantic sizes for just a few watts.
See the thread down here for some more numbers.

[https://news.ycombinator.com/item?id=17489462](https://news.ycombinator.com/item?id=17489462)

~~~
MichaelApproved
True but that's at 5c. What happens if we go to 10c differential? Is the gain
linear or does it become more productive as the differential gets higher?

A radioactive device that gives off that much heat wouldn't make sense for
something like your TV remote control. However, maybe it could help power your
off-the-grid house.

Does a radioactive material exist that could give off a few Celsius degrees of
heat for years?

Would it be feasible to have homes use that material (properly shielded)
without being a threat to national security and safety?

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okket
It's a whole subtopic with uses in satellites too far away from the sun
(Voyager), or rovers on surfaces where they don't see the sun constantly / to
much atmospheric interference (Curiosity). But I guess there are many more,
just not for your wristwatch or your home.

[https://en.wikipedia.org/wiki/Atomic_battery](https://en.wikipedia.org/wiki/Atomic_battery)

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asteli
Not used for wristwatches, but still in use powering pacemakers! How many
people are there still walking around with bits of Plutonium in them, I
wonder?

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pkilgore
Wonder how useful this might be for space travel.

Spaceships are essentially thermos bottles (metal tube surrounded by vacuum).

So lots of surface with large temperature differences.

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vinceguidry
A temp difference doesn't really exist when one of the substances is vacuum.
Without an actual material for the energy to flow into, all heat loss happens
radiatively. Which definitely can be captured, just not with this sort of
technique.

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gus_massa
The external temperature is the 3K level of the cosmic background radiation.
The external wall emits radiation but also absorbs radiation.

Probably the problem of this application is that it's much better to have very
good insulation in the walls than to try to capture the escaping heat and try
to use it for something useful as heating.

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sandworm101
>> For instance, it may be possible to charge your smartwatch during your
morning jog someday.

Already possible using 1970s mechanical tech. Or solar. Im sure there are
uses, but dont go with wristwatches for your explanations.

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okket
> Already possible using 1970s mechanical tech.

Or 1980s:
[https://en.wikipedia.org/wiki/Automatic_quartz](https://en.wikipedia.org/wiki/Automatic_quartz)

