eli5: What’s actually happening inside of a solar panel to turn light into electricity


as a follow up question, what are scientists doing to improve on them?

In: 7

The photoelectric effect was first explained by Einstein around 1900. Photons can interact with the electrons on the outside of matter, giving them more energy. It some unusual materials, like the silicon they make solar cells from, this extra energy can knock the electron loose from its silicon atom. In the solar panel, thin wires collect up these loose electrons as power. (That’s super over simplified.)

To improve them, scientists are looking for materials which get this effect from a broader range of photons. It would be ideal to be able to use the whole spectrum of light and even IR to produce power, but most current cells only use photons of specific energy levels, wasting the rest of them to heat up the panel.

Photovoltaic solar panels rely on the photovoltaic effect as the name implies

Light comes in the form of photons which each have a certain amount of energy to them. If you arrange a semiconductor so that the electrons on each side are at different energy levels, then when a photon comes it with enough energy it can smack an electron and give it enough energy to hop over the barrier. Its a bit like a water slide except instead of a ladder to get up everyone is waiting on a trampoline and occasionally a big enough rock comes it, smacks the trampoline, and launches them up so they can ride down the slide

The difference in energy levels between these two sides is called the bandgap and tells you how much energy you can get from each photon. If you catch one that has higher energy it’ll still release the electron but you only get the much lower band gap energy from it

If you only have 1 bandgap then the best you can possibly get from your solar panels is 33.7% because of how energy from the sun is distributed. Part of the gains have been narrowing in on the materials that’ll let us make that perfect bandgap to get 33.7% efficiency

The most efficient panels used in space get better efficiency by having multiple junctions. First they have a really big bandgap(tall water slide) that catches the highest energy light and gives the most energy, but things that aren’t caught there move down to a medium bandgap, and things that aren’t caught there move down to a small bandgap.

The current best solar cell made in a lab had 6 junctions with 6 different bandgaps and a lens concentrating the light on a small area(so they didn’t need to make a big expensive cell) hit 47.1% efficiency.

For the most part though, normal people want cheap panels because if you can get 20% efficient panels for a third the cost of 30% efficient panels then they’ll take up 50% more space but cost only 66% as much.

Thermal collectors and photovoltaic cells work to convert sunlight into energy in slightly different ways. https://youtu.be/2fNXZ5fDE6U