Would slapping a two way mirror on a solar panel increase the efficiency?


I’ll be honest, I know absolutely nothing about the science or the tech itself. It just seems like it would help by reflecting the light back at the panel (like trapping it I guess), instead of just bouncing off once. I’m just curious and this seemed like a good place to ask about it

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Two-way mirrors (or one-way mirrors, as they’re sometimes called) don’t let light pass in only one direction. They’re just a piece of glass that’s only *partly* mirrored. They reflect some light and transmit some light, in both directions.

The trick to such a mirror is that it’s installed in a location where one side is very dark and the other side is bright. When seen from the bright room, the reflection overpowers any light from the dark room, and it looks like a mirror. Seen from the dark room, the reflection is negligible compared to the light from the bright room, and it looks like a window.

The inefficiencies in solar panels isn’t predominantly from reflection. Mostly it’s either photons arriving that aren’t strong enough to dislodge electrons from the substrate (might energy that you can’t do anything with) or electrons that get recaptured before joining the circuit the panel has powering

A two way mirror is a piece of glass with an extremely thin coating of silver or aluminum on one side. This reflects roughly half the light that enters the surface while the rest passes through into the glass behind and out the other side.

If the mirrored layer was on the sun-facing side, then this would reduce the current output of the cell by half. It wouldn’t effect the efficiency of the PV cell itself, it would merely act like a pair of sunglasses, reducing the light iluminance reaching the cell in the first place.

PV cells typically have a relatively thick layer of aluminum, copper or silver as a backside contact for conducting current into the cell. This has the added advantage of reflecting any stray visible light that isn’t absorbed by the active region, back up towards the active layer. In practice this improves efficiency a few percent. It also has the advantage of helping conduct extra heat out of the cell, keeping it from getting too hot, which shortens the lifespan of PV cells.

The efficiency of modern PV cells is mainly limited by physical effects. Namely the cell is most efficient only on a barrow band of wavelengths. It cannot use longer wavelengths of light in the red and infrared range, which is either reflected or absorbed as heat without producing any current. Meanwhile the energy of shorter wavelengths in the blue range aren’t fully utilized, the extra energy ends up likewise as heat.

You don’t need a mirror to cause light to reflect. The glass on the front of a solar panel is already carefully designed to reflect as much light as possible back towards the silicon before it leaves the glass. This is done by controlling its thickness and adding surface textures.