
New Device Harvests Energy in Darkness - ColinWright
https://www.nytimes.com/2019/09/12/science/solar-energy-power-electricity.html
======
ar813
Hi there - I'm the lead author of this paper. Not a big fan of this particular
write-up.. it's not a solar panel at all! But happy to answer questions.

The NYT actually had a detailed write-up that I thought was quite accurate:
[https://www.nytimes.com/2019/09/12/science/solar-energy-
powe...](https://www.nytimes.com/2019/09/12/science/solar-energy-power-
electricity.html)

~~~
Danieru
Semi-off topic but you should knowledge-able in the area, but would there be
any potential in leveraging the permanent temperature differences which occur
10meters below the ocean? Light does not penetrate below 10meters and old
water is denser. Thus the ocean, away from land, has a permanent and
substantial potential energy difference between these two layers. Is it viable
to harvest this difference?

~~~
blistovmhz
Yes. It's called an OTEC (Ocean thermal energy converter) and it's a very old
idea. They are quite workable. In the simplest form, you have a 2 vacuum
chambers at the surface, and a pipe to the bottom of the ocean. You vacuum out
your pressure vessel down to around 3psi and let some warm surface water in
one end, while pumping cold bottom water into a radiator in the other. At
3psi, the surface water flashes to steam in vessel A, drives a turbine into
vessel B, and then condenses back into liquid water on the radiator. This
brings the system pressure back down to where you started.

In practice, you'd probably use the surface water to warm a working fluid that
is a gas at surface temperature and pressure, and then the system can stay at
atmospheric pressure.

The benefit of this system is that it also creates an artificial upwelling of
nutrients from the bottom of the ocean, which can be used to grow all sorts of
stuff. Was a big hippy fad idea back in the 70's.

------
seltzered_
Neat invention, frustrating article title.

paper link:
[https://www.cell.com/joule/fulltext/S2542-4351(19)30412-X](https://www.cell.com/joule/fulltext/S2542-4351\(19\)30412-X)
[https://doi.org/10.1016/j.joule.2019.08.009](https://doi.org/10.1016/j.joule.2019.08.009)

"We have highlighted the remarkable possibility and potential of generating
small amounts of power by radiative cooling at night using low-cost, off-the-
shelf, commodity components (less than $30 USD for our initial proof of
concept demonstration). In off-grid locations throughout the world, this
approach of generating light from darkness highlights an entirely new way of
maintaining lighting, entirely passively, at night. The power generated could
also be used to power small sensors in remote locations, with their lifetimes
not being limited by batteries but the lifetime of the thermoelectric module,
which can be an order of magnitude longer"

The invention seems more fitting for certain remote sensor applications rather
than say, lighting for an off-grid home that's already served by the various
solar-battery-lighting companies that've been around for over a decade.

------
sonofgod
I love this concept.

Sure, it'll never be a significant source of energy [if we plastered literally
the entire earth's surface with them at maximum theoretical efficiency, we'd
provide 1% of our electricity consumption].

But the sheer concept of "you know what, lets generate energy from THE VOID OF
SPACE, the ABSENCE OF HEAT" is deeply entertaining.

~~~
TeMPOraL
I had this weird, uncanny moment when I first realized that atmosphere being
transparent at some infrared bands means a device exploiting this is literally
cooled as if it was exposed to interplanetary space. It looks into the abyss.

~~~
jngreenlee
You can have a fun and cool similar effect if you get a $10 infrared
thermometer (I would say one with a laser for helping to point it). Useful for
cooking and food safety.

But then...go outside a night and point it first at the ground, then at any
clouds, and then right up into darkness. You'll see a big drop in temperature,
which is the absence of heat energy in the atmosphere itself...all the way out
into space.

I believe that the sensor has some type of angle to what it can detect, so
you're getting the average reading across a large cone of air/space at that
point. Also, the radiated heat along the depth of the cone would be "stacked",
so that you are viewing a 'cumulative' reading from the entire depths of that
cone, like an integral going into space.

~~~
ghego1
So what happens if you point it to the sun during daytime?

~~~
Dylan16807
Youtube says you get about 350F. The sun's angle is probably too small for a
proper reading. (And you get something like -15F for daytime sky.)

------
KaiserPro
From what I can tell this is a peltier
([https://en.wikipedia.org/wiki/Thermoelectric_cooling](https://en.wikipedia.org/wiki/Thermoelectric_cooling))
block.

The new(ish) bit is the fact that with a heatsink it can radiate heat from the
earth into the atmosphere.

however its 25mw per m2, to put that in comparison, this photdiode here:
[https://www.sparkfun.com/products/9541](https://www.sparkfun.com/products/9541)
looks like it can produce 11mw in full sun.

~~~
jfengel
The newish bit is that it's bypassing the atmosphere and radiating directly
into space. They actually try to keep the atmosphere off of it with
insulation, since the atmosphere warms it up to ambient temperature. The night
sky is cold enough to freeze water (and has been used for thousands of years
to make ice even in countries where the nighttime temperature is above
freezing).

There is a Peltier device at the core of it. That's old news. The new news is
increasing the temperature differential that drives the device. None of that
is new physics. It's just a first stab at trying to make one practical.

------
ColinWright
This reminds me of using a solar oven in reverse.

Take a heavily insulated box with a window on one side and put a parabolic
reflector in it. Point the reflector at the clear night sky, and you can
create ice at the focus.

All objects are in a balance between incoming and outgoing heat, so when all
the heat going out it sent into a sink - such as the clear night sky - the
object will drop in temperature.

The effect isn't huge, but it's real. The system described in the submitted
article here has nothing like the energy generating potential required to
become a sensible source of renewable energy, but it's a nice effect, and a
nice system.

~~~
dilippkumar
Can someone who knows how this works explain what's going on in terms of the
2nd law of Thermodynamics?

~~~
ColinWright
Consider a small body at the focal point of a parabolic reflector, and that
reflector pointed at empty sky at night.

You effectively have the body radiatively thermally connected to space, and
space is cold. So heat radiated from the object goes out to space, and nothing
comes back, and thus the object gets colder.

If doesn't work if there are clouds, because clouds are quite warm.

~~~
delinka
> ...because clouds are quite warm.

And are, therefore, radiating heat back into the small body via parabolic
reflector.

------
chungy
What's with the scroll behavior on the site? makes me not want to even be
there.

~~~
alexdumitru
I quit reading it because of the scroll behavior.

~~~
atrilumen
I couldn't read the first sentence because I wanted to zoom in a little.

------
sixstringtheory
Very interested in this, as someone thinking about how to set up an off grid
cabin here in Alaska. Last winter we hit a 112°F difference between inside our
cabin at 72° and outside at -40°. This seems like a way to harness some of the
heat drain while compensating for the accompanying darkness of the winter
months that would drive less photovoltaic generation. I don't know much about
solar alternatives so would love to know more from anyone who could suggest
things...

------
pseudolus
It's seems to be a variation on a simple thermocouple [0]. Underlying the
technology is geocooling and geoheating which have been around for quite some
time and are fairly mature technologies [1].

[0]
[https://en.wikipedia.org/wiki/Thermocouple](https://en.wikipedia.org/wiki/Thermocouple)

[1]
[https://en.wikipedia.org/wiki/Geothermal_heat_pump](https://en.wikipedia.org/wiki/Geothermal_heat_pump)

------
ziptron
It is not like a heat pump at all, it is a thermoelectric material. This has
been around for ages. Basically, the thermal gradient across a thermoelectric
material causes the flow of charged particles. See some of the links below.

They basically built an efficient heat sink (a material good at cooling itself
and anything that it is attached to) that radiates heat from one side of their
thermoelectric crystal while keeping the other side at room (or other)
temperature. This temperature gradient creates the current that they say can
run an LED.

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

[https://www.youtube.com/watch?v=6JH-
GgLe1xs](https://www.youtube.com/watch?v=6JH-GgLe1xs)

------
teilo
Yeah, but it's a gimmick. There's no way to make it useful because even at
perfect efficiency, it's not possible to generate a useful amount of power
given the required surface area.

~~~
boomlinde
Useful for what? The paper mentions off-grid sensors, which seems like a
useful application. Looks like the numbers are 0.5W/m² which means a square
meter of these could power e.g. an ESP8266.

It's obviously not going to power your home with those numbers, but it's a
little unimaginative to say that it has no useful application.

~~~
ctdonath
0.5W/m² is amusing, as my rule of thumb for solar power is 10W/m² (24/7/365,
all degradation considered).

------
shartshooter
Could you bury something like this in the ground all the time since the earth
is ~50° at 11’[1]. You could have those plates touching the earth which would
conduct heat away from the plate. 50° is pretty cool and would be running
24/7.

Would surrounding earth be able to sustain cooling a disk like this or would
the area just warm up right away and you’d lose any gains?

[1]
[http://www.duanesworld.net/duanesworld.net.sensors.htm](http://www.duanesworld.net/duanesworld.net.sensors.htm)

------
knzhou
That's really neat! If you only need a little power, you might even be able to
harness the 100 W of heat our bodies continually give off. You could press the
warm end against you to bring it up to human body temperature rather than just
ambient, which should increase the thermodynamic efficiency by quite a bit.
I'm imagining, perhaps, a handheld flashlight that powers itself using the
heat from your hand alone.

~~~
skosch
A small flashlight can (and has been) done, see e.g.
[https://hackaday.io/project/158857-body-heat-powered-
flashli...](https://hackaday.io/project/158857-body-heat-powered-flashlight)

------
d--b
I don’t understand, isn’t this harvesting the same energy as a heat pump?
(Warm earth, cold air)

~~~
Enginerrrd
At it's core, yes, but I think it's less "cold air" and more thermally
equilibrating with the radiative temperature of the night sky which is more
like 3 degrees Kelvin. So in essence you are lowering the temperature of the
cold sink until the ambient temperature is comparatively hot to extract work
out of your heat pump.

------
tiep
how it work? and how much if it going to be sale? this is will be good with
solar energy in future, when we can creating energy from day to night

------
GistNoesis
Reminded me of the phenomenon about starting a fire from moonlight and the
conservation of étendue. [https://what-if.xkcd.com/145/](https://what-
if.xkcd.com/145/)

~~~
quickthrower2
You could start a fire with moonlight + phosphorus.

------
JohnBerea
We should call it... dark energy

