
Pyroelectricity could extract energy from heat sources below 100°C - rbanffy
https://www.electronicsweekly.com/news/research-news/new-twist-old-technique-extract-electricity-low-grade-heat-2018-04/
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Someone
526 Watt/cm³? How should I interpret that? I doubt it’s by the volume of the
stuff covered with the film; it seems way too high for that (that would freeze
water in seconds, if I’m not mistaken)

The best I can think of is that it is by the volume of the film, but I find
that a weird way to express it, as it would seem to imply there’s little
difference between a thin film over a large area and a thicker one over a
smaller one.

But let’s go with that. Assuming a film thickness of 100nm (article says
“50-100nm thick”) = 10^-7m = 10^-5cm, one would ⁿ eed an area of 10⁵ cm² = 10
m² to get that 526 Watt of power out. Still seems high. If that’s how to
interpret that number, what kind of stuff do I need to cover with this film
for that to happen?

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pjc50
That is for the volume of the film, yes: (via scihub)

"PMN–0.32PT thin films are shown to provide record-breaking pyroelectric
energy con \- version, including: first, the largest energy density of 1.06 J
cm − 3 (at Δ T = 90 K, Δ E = 267 kV cm − 1 and f = 40 Hz; Fig. 4a), which is
made possible because of the large field-induced value of π and the ability to
apply large electric fields maximizing the electrical work ( ∮ ⋅ EP d ).
Second, the largest power density of 526 Wcm − 3 (at Δ T = 56 K, Δ E = 267 kV
cm − 1 and f = 1,000 Hz; Fig. 4b) that is real \- ized because the power
density scales directly with cycling fre \- quency, which can be increased
because the thermal time constant of the thin-film geometry is small."

Note the operational constraints. You have to apply a varying electic field
_and_ a varying temperature.

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boxcardavin
The Carnot limit applies specifically to heat engines but later proofs on the
2nd law of thermodynamics still cap the conversion of heat to useful energy.
As long as you keep that in mind, 19% Carnot efficiency is really impressive
for a system like this with a small temp difference and no moving parts. I
find their watts per cubic region an odd way to measure it given that you need
heat flow across a surface to generate juice.

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pjc50
Pyroelectricity is a little different from thermoelectricity - it's only
activated by a _change_ in heat levels.

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hinkley
Years ago we added piezoelectric films to skis to make them more shock
resistant.

I wonder when someone will add pyroelectric film to something to make it more
resistant to _thermal_ shock?

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21
Can you cover a building in this and generate (some) electricity for the air
conditioners when it's hot outside?

~~~
marshray
IANA thermodynamicist, but I suspect the resulting system could not be more
efficient than either the heat pump or the pyroelectric charge pump by itself.
So if this conversion process is really that great, you would end up replacing
your heat pump with it instead of combining them.

I think this only applies if we're constraining the temperatures to typical
summer outdoor/indoor cooling applications. Different technologies are going
to have different temperature ranges at which they are most efficient, so for
something like steam power generation multi-stage systems are common.

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agumonkey
Let's coat ICE engine hood with this and gather some waste heat energy.

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sandworm101
The hood is exactly the wrong place. Blocks, radiators, even oil pans would be
far better.

But imho the real market for these will be in low-power environments. Or
defense: submarines have near-unlimited heatsink potential and lots of <100
heat sources.

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arethuza
That made me wonder if anyone had tried tracking submarines based on the heat
they leave behind - turns out the Soviets had a technique that integrated
various sources including heat :

[https://www.popularmechanics.com/military/navy-
ships/a28724/...](https://www.popularmechanics.com/military/navy-
ships/a28724/submarine-sonar-soks/)

~~~
virmundi
The Swedes sunk the USS Ronald Regan in war games using a sterling engine
powered sub. It makes it hard to track since it doesn't have the traditional
explosion noises of a diesel and it lacks the heat sink noise of water cooling
a nuclear core.

[https://www.youtube.com/watch?v=saCdvAp5cow&t=354s](https://www.youtube.com/watch?v=saCdvAp5cow&t=354s)

~~~
djrogers
Diesel subs don’t operate their engines while submerged unless they are
recharging in safe waters, so there aren’t any ‘explosion noises’. They have
batteries that are used for propulsion, and the Diesel engines are technically
generators, as their propulsion system is electric - like a train.

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toblender
I'm surprised no one mentioned bitcoin mining... this would be great to
capture the excess low grade heat and change it back into electricity.

~~~
myfonj
Exactly. Or CPU/GPU/any chip cooling in general.

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marshray
> 1.06J/cm3

Energy per volume?

That would make sense for, say, battery storage but can anyone explain how it
describes an energy conversion process?

