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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You can do it with PVT (Photovoltaic Thermal) panels, they have tubes filled with water running on the back of the solar panel. This captures the heat. This has as added benefit that the solar panels are effectively cooled and therefore operate at higher efficiency.
I read somewhere that they achieved 86% total efficiency once with this system, which is very high for a solar energy system. But I don’t know how it compares cost wise.
https://www.engineering.com/story/photovoltaic-thermal-system-achieves-86-efficiency
I’ll add to some of the other responses, linking some images that may be helpful to clarify what’s going on. First off, we can graph the energy from the sun that hits earth to see how much of each wavelength of light we’re working with. The industry standard graph is called AM1.5, and it looks something like [this](https://cnx.org/resources/5c23fc928d34f39f76cf239208c0b86ab90bb5a3/graphics1.jpg). As you can see, there’s a lot of energy coming from frequencies around visible light, and less coming from farther out in the infrared and very little from ultraviolet.
It’s also worth clarifying that shorter wavelengths of light (to the left on the x axis) carry more energy *per photon* than longer wavelengths.
Now we come to solar photovoltaic (PV) panels. To oversimplify, they generate electricity by using a photon of light to bump an electron up an energy level. The amount of energy it takes to do this is a property of the base material, called it’s band gap. Photons that don’t have enough energy (have wavelengths too long) can’t get an electron over that gap, and so provide no electrical energy. [here](https://www.solarquotes.com.au/blog/wp-content/uploads/2017/08/pvspectrum.jpg) is a visualization of this on the AM 1.5 graph. Note that everything to the right of the band gap is wasted. So, it would appear that the best solar cells would use materials with a very small band gap, so we can use the largest possible fraction of the light that hits the cell.
Unfortunately, when an electron makes that jump, we can only get the amount of energy equivalent to what it took to bump the electron up and over the band gap. Shorter wavelength photons that carry excess energy can only contribute a small portion to electrical energy; the rest is wasted as heat. So, what we actually want is a material with a bandgap small enough to allow us to capture a large percentage of the available light, but still big enough to allow us to use a large portion of the energy from the more plentiful, higher energy visible light. [here](https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcSuzowDUCeliBZ_SDUNg6Y_4jEIDMAsbxefhg&usqp=CAU) is a visualization of that tradeoff. Luckily, as we can see, among some of the more exotic materials, there’s also a very common industrial material, silicon (Si) right near the peak of efficiency. This is why most solar panels use silicon cells. It’s also worth noting that the particular size of the silicon bandgap allows it to use a portion of the infrared light, as well as the visible and UV.
Now, there’s one more wrinkle. If we don’t care about electrical energy, and instead, we want just heat energy, all we need to do is have a totally absorbtive (black) surface across all wavelengths. This is pretty easy to do, but heat is less useful and harder to transport or store than electricity. But if heat’s what you need, there’s potentially a lot more solar energy available for the taking! An example [here](https://www.youtube.com/watch?v=FKhszB4E1_M).
It depends on if you mean a solar panel or photovoltaic panel. The first is basically the heat of the sun it heats up a pipe and this is connected to a water tank to heat up water for cooking or showering, instead of using gas.
The second, photovoltaic, uses photons from the sun. It’s basically a semiconductor aka diode which takes in photons and generates an electric current using a process known as the photoelectric effect
So I guess to answer your question. Solar panels use IR radiation and PV panels use visible lught from the sun however PV panels also use a tiny bit from the IR and UV spectrum. For example an LED emits light in the visible spectrum but some IR and UV too
I hope this makes sense
I remember watching a video about transparent solar panels, or rather, windows with the ability to gather electricity from non-visible solar rays. The solar panel was in the window, and it was a transparent window. They proposed as a way to use all the surface area of a building with a glass exterior, transforming it to a power generating structure.
You could collect lower energy infrared than current commerical panels. The problem is that cells which absorb it will have lower voltages, so you get less power per bit of light. Efficiency of those cells will also be a problem unless you can keep them cold.
Ah, something I can answer. There is currently research going into capturing the infrared light that others have mentioned. It’s a process called photon up-conversion. Infrared photons are not energetic enough to induce a flow of electrons, but if they can be combined chemically and electronically into higher energy states, then they can be used to generate electricity.
Research is going into discovering molecules that can achieve such feats and how they can be applied and integrated into photovoltaics.
Any photon with energy greater than the bandgap of the material of which the PV cell is made can be absorbed. However most of the sunlight energy is in the near infrared and visible regions.
Silicon has a bandgap of ~1.12 eV (wavelength less than 1100nm), so any photon with greater energy will be absorbed, and energy in excess of 1.12 eV per photon will be dissipated as heat. There are some technicalities which reduce the absorption efficiency near the 1100nm.
If you want more efficient PV cell at shorter wavelengths you can go to a material with greater bandgap.
If you want to absorb 1500 nm you can go to lower band gap energy like indium phosphide.
“Sunlight” is not just the visible spectrum. Sunlight includes a ton of IR and UV. When you feel the sun’s glow, that’s IR radiation (or “light” if you want).
Visible light is 400-700nm. All photovoltaic solar cells use a broader band than this. It varies with the specific chemical composition/technology but all pull energy from lots of the UV spectrum (which is low energy) and some of the IR spectrum (high energy but creates unwanted heat).
In a sense solar thermal panels are “tuned” for IR.
Yes, they can. What you’re thinking of is something called a thermophotovoltaic cell. Some people have mentioned photovoltaic thermal panels, which are a bit different in function and execution, but also use the infrared region of the solar spectrum for useful work.
Photovoltaic thermal panels absorb infrared energy as heat and use the heat to do useful work (e.g. heating water in a closed heating system). Thermophotovoltaics convert infrared energy directly into electricity via a semiconductor devices that operates on similar principles as classic photovoltaic cells.
So why don’t more people know about photovoltaics? There’s a few reasons. First, the materials used in these cells to get the required material properties are much more scarce and fragile than in photovoltaic cells. Second, the amount of energy that can be harvested by these devices is much lower than cells in the visible range. Third, the fabrication methods necessary to make these cells are extremely elaborate, due in part to the materials’ delicacy and the required structure of the devices.
That said, there is also interesting research being done where thermophotovoltaic devices are used to harvest heat from extremely high temperature processes (e.g. metal foundries). The principle of operation between harvest heat from a foundry furnace and harvesting energy from the sun operates on exactly the same principle. It’s just that the sun is much, much, much, extremely much hotter, so it’s much easier to do with the sun.
The sun (sunlight) emmits much much more than just visible wavelengths. Pretty much all the wavelengths.
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