from the you-know-the-night-time-is-the-right-time dept.
Researchers used radiative cooling to generate enough to power LEDs or charge a cellphone
By taking advantage of the temperature difference between a solar panel and ambient air, engineers have made solar cells that can produce electricity at night.
Compared to the 100 to 200 watts per square meter that solar cells produce when the sun is shining, the nighttime production is a trickle at 50 mW/m2. "But it is already financially interesting for low-power-density applications like LED lights, charging a cellphone, or trying to power small sensors," says Shanhui Fan, a professor of electrical engineering at Stanford University who published the work along with coauthors in Applied Physics Letters.
Fan and his colleagues harnessed the concept of radiative cooling, the phenomenon by which materials radiate heat into the sky at night after absorbing solar energy all day and that others have tapped before to make cooling paint and energy-efficient air-conditioning. Because of this effect, the temperature of a standard solar cell pointing at the sky at night falls below ambient air temperature. This generates a heat flow from the ambient air to the solar cell. "That heat flow can be harvested to generate power," Fan says.
[...] The team tested their prototype TEG-integrated solar cell for three days in October 2021 on a rooftop in Stanford, Calif. The demonstration showed a nighttime power production of 50 mW/m2. The team estimates that in a hotter, drier climate, the same setup could generate up to 100 mW/m2.
[...] "In principle, it could be possible to engineer the thermal-emission property of the solar cell to optimize its radiative cooling performance without affecting solar performance," Fan says. "Our theoretical calculations point to the possibility of a few hundred milliwatts or maybe even 1 watt."
Journal Reference:
Sid Assawaworrarit, Zunaid Omair, and Shanhui Fan, Nighttime electric power generation at a density of 50 mW/m2 via radiative cooling of a photovoltaic cell [open], Appl. Phys. Lett. 120, 143901 (2022)
DOI: 10.1063/5.0085205
(Score: -1, Troll) by Anonymous Coward on Friday April 22 2022, @08:33PM (4 children)
It doesn't reflect well on Applied Physics Letters, either. No problem with the technical content per se. Just reminds me about how the MIT physicist rediscovered how to model an weakly coupled transformer and the skin effect of conductors and called it Witricity.
Both these examples are physicist-types taking well-understood phenomena and hyping the crap out of it.
50 mW? How about include an extra 2 cm^ squared on my solar panel and add a rechargeable coin cell. Oh, but that wouldn't get me a paper in Applied Physics Letters and tenure at Stanford.
(Score: -1, Offtopic) by Anonymous Coward on Friday April 22 2022, @10:39PM (1 child)
The author list reminds me of that old joke that begins "A Chinaman, a jihadi and some random foreigner walk into a bar..."
(Score: -1, Flamebait) by Anonymous Coward on Friday April 22 2022, @10:48PM
and an alcohol demented republican gunned them all down.
(Score: 0) by Anonymous Coward on Friday April 22 2022, @10:42PM
Night time electrical generation efficiency is 0.03% that of the daytime. Adding extra daytime cells to charge a battery will be far more economical. The other plus: no new solar cell technology is needed. It's already here and in use.
(Score: 0) by Anonymous Coward on Saturday April 23 2022, @11:01AM
Guess someone from Stanford or Applied Physics Letters read this comment… or maybe the agency that funded this.
(Score: 0) by Anonymous Coward on Friday April 22 2022, @08:33PM
Solar cells tend to run hot anyway so this should (slightly) improve their daytime efficiency.
(Score: 4, Informative) by drussell on Friday April 22 2022, @09:12PM (3 children)
No, they don't...
(At least not enough to be useful.)
(facepalm)
(Score: 2) by coolgopher on Saturday April 23 2022, @12:25AM (1 child)
For a rather amusing reality-check, I'd suggest this EEVblog episode [youtube.com] .
(Score: 2) by drussell on Sunday April 24 2022, @06:45PM
Yeah, I had seen Dave's video already, as well...
(Score: 2) by bradley13 on Saturday April 23 2022, @08:04PM
I saw this a while ago, and did the math. Not gonna dig it up now, but we're talking about megawatt installations producing milliwatts. There's no way this is worthwhile.
Everyone is somebody else's weirdo.
(Score: 0) by Anonymous Coward on Friday April 22 2022, @09:46PM
la wik says annual us energy usage is about 25155 terrawatt hours. if my mafs(*) are correct, that's 503100000000000000 50mwh leds. light 'em up!
*: 25155 * 1000000 * 1000000 * 1000 / 50 = 503100000000000000
(Score: 0) by Anonymous Coward on Saturday April 23 2022, @05:57AM
i noticed my panels to be wet during certain (dry) nights. sometimes enough to drip.
the grass/weed also grows more around the bottom edge, where the water drops down...
for windtraps, i suppose they need a non-soaking surface (non porous), be light in mass, and conduct heat really well. also they need to be isolated from the "weight carry structure" really well.
it's maybe like trying to "hold" a closed, light, conducting surface of multiple square meters with four needle pins. the support structure should be massive and well protected from sunlight and thermally well grounded to the ground. nevertheless this "massive bottom" needs to be isolated from the dew, solar collector. it's a engineering question of reducing the thermal flow of support structure to the condensing surface but at the same time not flying away during any storms.
it also seems that the "condesing" surface needs to be rigid. any "flapping in the wind" is kindda un-inviting for dew drops to form.
evaporating or water lose could be reduced by making a "french drain" (ditch filled with stone) to get the "drip.drops" to accumulate further in the ground, where it's cooler and dark and roots live.
carrots should work. 50mW carrots ftw!
(Score: 0) by Anonymous Coward on Saturday April 23 2022, @11:11AM
Had a customer call up to inform that the gov came checking his PV installation as they suspected he was faking the numbers to get more green energy certificates. Living next to a stadium that uses high power lighting in the direction of your house tends to make your panels generate significant nighttime power as well :)
50mW /m² really doesn't sound like much at all though. A regular panel + battery is going to be much better.