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A concept paper published in ACS Photonics, describes a photovoltaic cell that works at night.
According Jeremy Munday, one of the paper's authors and a professor in the Department of Electrical and Computer Engineering at UC Davis
a specially designed photovoltaic cell could generate up to 50 watts of power per square meter under ideal conditions at night, about a quarter of what a conventional solar panel can generate in daytime
The described cell is thermoradiative and emits infrared radiation to space, which has a much lower than Earth temperature of 2.73 Kelvin.
"A regular solar cell generates power by absorbing sunlight, which causes a voltage to appear across the device and for current to flow. In these new devices, light is instead emitted and the current and voltage go in the opposite direction, but you still generate power," Munday said. "You have to use different materials, but the physics is the same."
The device would work during the day as well, if you took steps to either block direct sunlight or pointed it away from the sun. Because this new type of solar cell could potentially operate around the clock, it is an intriguing option to balance the power grid over the day-night cycle.
Journal Reference: [Nighttime Photovoltaic Cells: Electrical Power Generation by Optically Coupling with Deep Space, ACS Photonics (DOI: 10.1021/acsphotonics.9b00679)
(Score: 4, Interesting) by JoeMerchant on Sunday February 02 2020, @02:53PM (7 children)
Does this mean that space based solar arrays can become two sided for a 25% output boost?
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(Score: 1) by RandomFactor on Sunday February 02 2020, @03:34PM (1 child)
It sounds like a good fit, spacecraft already have to radiate heat anyway so getting power from doing so could make sense.
I thought about the feasibility of making two sided arrays and flipping them for daytime vs nighttime use on Earth. Same general idea, although I wouldn't want a bunch of flipping/shuffling panels on my roof, however it might work for industrial sized solar farms.
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(Score: 3, Interesting) by Coward, Anonymous on Sunday February 02 2020, @04:11PM
Yay, let's add thermal resistance to the dissipation path! Engineers are going to love that.
(Score: 4, Informative) by Immerman on Sunday February 02 2020, @03:38PM (4 children)
Nope. Shipping to orbit is so expensive that you'll generally go with the high-end efficient solar panels of at 30+% efficiency. You also get almost 40% more sunlight reaching the panel without the atmosphere in the the way. Combined, you're generating at least 1400Winsolation * 30%(?) efficiency = 420W
Assuming these panels worked just as well in orbit, they'd only produce an extra 50W, or around 12%
That said, they might be more efficient as well - the solar panels likely get lot hotter than ambient earth conditions, and in space the radiating side of the panel isn't also recieiving radiation from the atmosphere, which probably cuts efficiency on Earth.
Of course, the big question is weight - if these could be laminated to the back of solar panels with no additional structure and minimal additional weight, then they could well be worth it. Otherwise it's probably far more weigh-efficient to just add more solar panels.
(Score: 2) by JoeMerchant on Sunday February 02 2020, @04:37PM
That was my thought, you're making these big "wings" with an essentially unused surface, so why not use it?
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(Score: 0) by Anonymous Coward on Sunday February 02 2020, @07:11PM (2 children)
They wouldn't work in space. They work on the heat difference between the ambient environment and the radiant temperature of the sky. Without the ambient heat flowing into the back side, power output would drop to zero at the temperature equalised.
They might be useful in tropical cities, as they are basically ejecting heat to space and would cool the area around them. Not as much as just painting stuff black, but if you do that it gets hot during the day. I do like the idea of putting them on all the industrial roofs, with solar cells on the other side and flipping them sunrise/sunset.
(Score: 3, Informative) by Immerman on Sunday February 02 2020, @07:39PM (1 child)
The "ambient environment" on the warm side would be the solar panels themselves - which might well be considerably warmer than they would be on Earth since they're big dark panels that can only shed energy through radiant cooling.
Even if the solar panels are 30% efficient, that still leaves 70% of the incoming energy being either reflected or absorbed and converted to heat - and 70% of orbital solar energy is roughly the same as 100% of sea-level solar energy.
The radiant temperature of the sky would also be FAR lower in orbit. On Earth it averages around around 0C, though it cloudless desert nights can commonly get as cold as -50C, so you're talking maybe a 20-60C difference. The tropics are actually the worst, as warm humid air can bring the sky temperature up to 20C or more, not much cooler than ambient. Space in comparison is around -270C, so about 5x to 15x the thermal difference. If power output from the panels scaled similarly it you might end up actually rivaling the power from the solar panels.
(Score: 0) by Anonymous Coward on Monday February 03 2020, @02:32AM
Solar panel have to eject a significant amount of heat. Putting these on the back to extract energy would block that cooling and probably reduce their efficiency and cost you more than these produce.
If the stuff can be made cheap and efficient enough it might be economical to face the 'hot' side towards the sun, and use a mirror so that the 'cold' side sees a different part of the sky. Flipping it so that at night the 'hot' side faces the ground and the cold side faces space could give you panels than generate continuously,