eli5: Do solar panels only work with sunlight, or can they be tuned to capture energy from other wavelengths outside the visible spectrum?
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The thing is, nothing we have available is as bright as sunlight, in nearly any spectrum. The biggest source of infrared is the sun. The biggest source of ultraviolet is the sun. The biggest source of *neutrinos* is the sun.
Most research into other spectrums of solar panels are just to capture more energy from sunlight. If you’re thinking that switching spectrums might allow solar panels which can work at night, unfortunately at night there is just simply less energy available for that kind of capture.
Solar panel?
No, others have given the reasons why, but what you may be interested in is this.
https://en.m.wikipedia.org/wiki/Rectenna
To my understanding, as long as the frequency of light is lower than the operating frequency of the diode it will convert any light into electricity
The only problem is cheap, mass produced diodes that can at most convert from microwave or far infrared…I think. I am rusty with this and not the most confident.
Edit 1: I Remembered a bit more.
For UV+Light, there is a way of generating power, (not solar panels sadly) which involves alternating thin conducting plates. As the photon goes through the plates they occasionally bump into the atoms (or even the electrons themselves for gamma) generating a very small, but somewhat usable, charge.
Also, there is a case where plants? turn radiation into energy
https://en.m.wikipedia.org/wiki/Radiotrophic_fungus
These fungi are one such case
Yes and no.
When a photon hits an electron, if the photon has the right amount of energy, then the electron absorbs the photon and its energy and it can “jump” to a higher energy level (essentially allow it to orbit faster, farther away from the atom’s nucleus). With enough energy, the electron can completely leave the atom, a process called ionization (because when it leaves, the atom becomes a positively charged ion).
In the photovoltaic effect, this effect is exploited to get electrons to leave their atoms and be re-captured by a different material. The migration of electrons creates a charge difference between the two materials allowing current to flow.
Different materials have different wavelengths that work best, which means that a typical panel is made to capture whatever wavelengths are most abundant, particularly visible light.
UV wavelengths are higher energy than visible light, but there’s less UV than visible light. I believe there are multi-layer panel designs that are already commercially available that are able to capture additional wavelengths like UV.
So no, a particular material is going to have only some wavelengths that work for it.
But yes, because there are different materials and manufacturing techniques that allow us to absorb energy from other wavelengths.
sunlight consists of more than just the visibile light. Silicon solar cells (basically what you get everywhere) are tuned to be best at a specific wavelength (around 600nm), but absorb a spectrum from about 300 nm (UV) til 1200 nm (IR) light. One theoretical limit for these cells is around 33% of all the energy hitting the solar cell.
So yes, more than the visibile spectrum is used to generate electricity, and you can also use other materials to absorb other parts of the spectrum better.
Yes, researchers recently successfully tested a solar cell that works at night using the energy the earth absorbs during the day and then invisibly radiates at night in the infrared portion of the spectrum.
https://www.pv-magazine.com/2022/05/18/australian-researchers-crack-nighttime-solar/
So first things first: sunlight includes light outside the visible spectrum. The sun is a[ blackbody radiator](https://en.wikipedia.org/wiki/Black-body_radiation). What we call sunlight is a a whole spectrum of wavelengths all the way from radio waves to gamma rays. The amount of light emitted in each part of the spectrum is determined by [Planck’s Law](https://en.wikipedia.org/wiki/Planck%27s_law), which is a function of the temperature of the sun. The concept of visible light is only relevant to us as humans, because it is simply the range of wavelengths we are capable of perceiving with our eyes. It is no coincidence that the sun shines most intensely in the visible spectrum; humans evolved to see the wavelengths most prevalent in their environment.
As for solar panels, the answer is yes, and to a degree they already are. The way a solar panel works is that a junction of two semiconductor crystals is created. The material properties of the crystals are different from each other, and this creates an interesting phenomenon in how they react to light. An incident photon can collide with an electron in one of the crystals, and bump it into the other. This turns one crystal slightly positively charged (due to missing an electron) and the other slightly negatively charged (due to an extra electron). Where you have two different charges, electricity will flow, and voila, you have a solar panel.
The two crystals have what’s called a “bandgap,” which can be thought of as the energy difference between them. An electron has to be boosted by at least this much energy in order to make the jump, and will release this much energy when it flows back as electricity. In practice this means that an electron will only jump if it is hit by a photon of at least this much energy. This creates an interesting optimization problem:
* Set the bandgap low, and more of your photons will induce a jump, but you get less energy per-jump, even from high-energy photons.
* Set the bandgap high, and you get more energy per-jump, but fewer of the photons will induce a jump.
So in one case you are losing energy by failing to capture low-energy photons, and in the other you are losing energy by only capturing a small percent of the energy in the high-energy photons (regardless of photon energy, you only capture the value of the bandgap per photon). There is a sweet spot where the amount of energy you can collect is maximized, and that’s the bandgap that we target for solar panels. These panels are already capturing photons above the visual spectrum, they’re just not wringing as much energy out of them as they could, because they have their bandgap set to ensure they capture the bulk of light in the visible spectrum as well. There are such things as “multijunction” solar panels which have multiple bandgaps stacked one on top of the other, and the high-energy photons are captured by the high-bandgap junctions, and so on.
[Multi-junction solar cells](https://en.wikipedia.org/wiki/Multi-junction_solar_cell) DO capture infrared energy.
Anything above 700 nm (up to 1,000,000 nm) is infrared.
Figure C on the linked article shows how Multi-junction solar cells absorb plenty of light above 700 nm.
As other responders have said: combining different semiconductors in multi-junction cells makes use of this. The first adopters at large scale seem to be First Solar along with Sunpower:
https://pv-magazine-usa.com/2022/04/01/sunpower-in-late-stage-discussions-with-first-solar-to-produce-solar-modules-with-tandem-technology/
CdTe harvests more of the short-wave spectrum along with Silicon harvesting the longer wavelengths of the sun’s spectrum.
Well we can extract energy from any wavelength we choose to. But panels may not be the ideal setup for every means of electromagnetic spectrum energy extraction. For radio waves for example, if you wrap a toilet paper roll core with no 32 enameled copper wire, and you can get one of those radio crystal diodes, use a coat hanger as a modulator to adjust which part of the coil is the contact point, you have a radio that can work on say a cheap pair of 3.5mm earbuds that will actually let you hear radio stations, no batteries. It runs on the radio station itself. It is literally a radio without the amplifier, or without anything else other than the diode and the coil (which acts as a means to tune to different channels). Off top of my head I will guess it’s an AM radio, but maybe I am wrong
Edit yes foxhole radio is AM as I thought
It’s called a foxhole radio and its existence proves that different wavelength doesn’t stop extraction it just changes how to go about achieving it.
I burn my yard debris in front of my panels at night. They produce, enough to charge even, while the fire is going, so they react to more than just sun light.
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