Solar panel with nighttime power generation

[GordMay]

‘Thermal batteries’ could efficiently store wind and solar power in a renewable grid
Stored as heat in a bath of molten material, extra energy could be tapped when needed.

”... A team at the Massachusetts Institute of Technology (MIT) and the National Renewable Energy Laboratory achieved a nearly 30% jump in the efficiency of a thermophotovoltaic (TPV), a semiconductor structure that converts photons emitted from a heat source to electricity, just as a solar cell transforms sunlight into power. [1]

“This is very exciting stuff,” says Andrej Lenert, a materials engineer at the University of Michigan, Ann Arbor. “This is the first time [TPVs have] gotten into really promising efficiency ranges, which is ultimately what matters for a lot of applications.” Together with related advances, he and others say, the new work gives a major boost to efforts to roll out thermal batteries on a large scale, as cheap backup for renewable power systems.
The idea is to feed surplus wind or solar electricity to a heating element, which boosts the temperature of a liquid metal bath or a graphite block to several thousand degrees. The heat can be turned back into electricity by making steam that drives a turbine, but there are trade-offs. High temperatures raise the conversion efficiency, but turbine materials begin to break down at about 1500°C. TPVs offer an alternative: Funnel the stored heat to a metal film or filament, setting it aglow like the tungsten wire in an incandescent light bulb, then use TPVs to absorb the emitted light and turn it to electricity ...”

More about ➥ https://www.science.org/content/arti...renewable-grid

[1] “Thermophotovoltaic efficiency of 40%” ~ by Alina LaPotin et al
➥ https://www.nature.com/articles/s41586-022-04473-y

[catalystcat]

This is very interesting in terms of the prospects of heat engines. However, there is a huge distinction between (somewhat) practical heat engine design and the Stanford thermal PV project - the delta T.
The 40% heat engine relies on an input temperature of well over 1500C with a large temp drop between the sides of the heat engine. The input source would typically be part of a larger system that uses high heat (a furnace, industrial process, etc.). One could even generate heat near this range burning fuel. But, that puts it into direct competition with regular energy generation without their myriad issues, including their use of GaAs based materials and the difference between their lab version optimization and a system with real world constraints. Still, it's impressive engineering and as a co-generation system, it has more promise. But, even their it is blown away by tech such as the Modern Electron cold cathode heat engine that has higher efficiency and has moved from the lab to real world devices and customers.
As for the night time solar, their will always be constrained by the limited energy available from the low delta-T of such passive emission systems. If you look at tbheir equation 5, you see the maximum power depends on delta T squared. And, their power is limited by limitations on the solar panel's ability to radiate toward true blackbody. (It's no coincidence that they used a rooftop in the desert to get maximum delta T and minimum effects of atmospheric transparency).
They are also using mid/long IR wavelengths to take advantage of the transmission window (pretty similar to what IR imagers do) meaning that they can only take advantage of a portion of the thermal spectrum.

In any event, with the temps they are using and VERY idealized modeling, they get a maximum theoretical energy of 50-150W/m2 which is pretty much wishful thinking (e.g., it assumes they get 100% of the energy transmitted to their ideal black body, zero resistive loss, idealized Seebeck coefficients, and ideal thermocouples.) I won't even go into how they also had to add a bunch of thermal engineering (see fig 2 of the Stanford paper) to get this far.

So, it's cool physics. But, it's not really practical for more than really low power things like sensors. It might be more practical for things like satellites that already have large arrays and inherently better transmission to black body space.

[rossdv8]

The radiation is just not there at night, no matter how efficient the panels are.

We've been generating enough electricity from a single 80W solar panel at night to power a string of 4 metre string of LEDs for several years here. That is with NO battery - just the LEDs connected directly to the panel (via about 10 metres of twin core)

Admittedly they only come on when the lightning flashes, or sometimes in bright moonlight, but it is interesting to see several metres of lights come on apparently out of nowhere.

I've been wondering when someone would find a way to harness available night light in some proper form.

It is out there - all over the place, just it seems, at the wrong frequency to be useful.

[catalystcat]

To be a bit nitpicky on this topic (partly because it matters with respect to how much power is available in the idealized case and partly because I kind of nerd out on this kind of stuff), there is radiation available at night, even ignoring what most people refer to as light and ignoring esoteric stuff like nuclear radiation, gamma particles, etc.
The radiation is outside the visible range and is thermal. Hot/warm things give off thermal radiation in the mid/long IR.
The paper focuses mostly around 8-15 microns, just like a typical night vision camera. (though there is a bunch at even longer wavelengths that struggles to escape). Their true physics analysis relies on the energy available as the photons try to find a true blackbody absorber. It's not a lot.
Remember, the longer the wavelength the less energy its photons have. So, UV photons are a lot more energetic than long-IR (but less than Xray).

So, there is optical energy available. It's just not very much and really hard to use, and depends on the delta T.

[steveberl]

Maybe this would be useful for very low power remote sensor applications. Usually these would have a solar panel and a small Li battery to run through the night. The cycle count on the battery can be the limiting factor of the lifetime of such a device. This tech might let you build one with no battery required.