eli5: Do solar panels only work with sunlight, or can they be tuned to capture energy from other wavelengths outside the visible spectrum?


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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A follow up question: How much of the energy is stopped by clouds? Most likely some wavelengths pass through them easily.

The original solar panels did this – they were essentially water pipes that absorbed heat (ie IR radiation) from the sun, and fed into your hot water tank. Photovoltaic solar panels (ones that generate electricity) work by exactly matching the incoming photons to specific energy gaps in the material, meaning they can excite electrons by exactly the right amount. So in principle I guess you could try and find/design material that would work for IR or UV, such things probably already exist, but the issue is that the sun puts out the most energy at visible light wavelengths (possibly why we evolved to be able to see it and not other wavelengths). So if you’re going to use something to soak up as much sunlight energy as possible, it’s best to have it capturing the visible light. I think there are some panels which stack a few different materials to get a wider spectrum of absorption, but it gets difficult and expensive to do that I think, not least because you need the first layer to be transparent to what the second layer is trying to get power from.

The energy we get from the sun is 43% visible, 53% infrared and 4% ultraviolet.

Ultraviolet contains the most energy, but the limited quantity makes it difficult to make use of. If we adjusted existing panels, it would be expensive and would not add much – they still wouldn’t work at night, but would work better in cloudy conditions.

Infrared contains the least energy, which makes it difficult to use for electricity generation. It can be used to heat water, for example, directly, and there are systems that do this. Generally, this is done to help keep the panels cool, which makes them do their normal job better as well.

You can make panels that work at other frequencies, but the bulk of the energy we get is in the visible spectrum. Our atmosphere is rather opaque to a broad range of infrared wavelengths, and the ozone layer only allows a portion of UV radiation through. Areas below infrared or above ultraviolet just don’t have enough irradiance to produce useful amounts of power.

They can get energy from other wavelengths as well, but the material in them needs to be able to catch those wavelengths. High quality modern panels can catch six different wavelength areas to have an efficiency of about 40%.

They are still expensive to make (they have about 140 layers), so they are the sort of panels you will find on space ships, but not yet on houses.