How solar panels actually work?

Question

How solar panels actually work?

In: 75

Answer 1

I think first you need to understand how semiconductors work, otherwise every explanation just boils down to input light output electricity which tells you absolutely nothing you didn’t already know.

So, enter a basic [PN junction, a diode](https://en.wikipedia.org/wiki/P%E2%80%93n_junction#/media/File:Pn-junction-equilibrium.png). P and N being semiconductor materials doped with positive and negative ions respectively. N doped semiconductor has an excess of electrons which leads to conventional conductivity with negative charges, P doped has a shortage of electrons which leads to conductivity of holes – a lack of a electron in crystal lattice works as a positive charge carrier.

Such a junction can be voltage biased two ways. If it’s reverse biased then negative terminal is connected to P type material and attracts positive charges or holes. Positive terminal is connected to N type material and attracts negative charges or electrons. As charge carriers in semiconductor are pulled away from the junction, it’s becomes a isolator, there are no charge carriers to conduct electricity there. The diode does not pass current.

Terminals are flipped if PN junction is forward biased. Holes are pulled towards the N terminal and electrons are pulled towards P terminal, two conductive materials meet and current can pass.

Now interesting thing happens at the junction where excess electrons from N semiconductor recombine with holes in P semiconductor. Holes are really only places in crystal lattice that are short of an electron. So there is a difference in energy levels and electron falls down that potential gradient. Energy can’t really disappear like that so the electron emits a photon in the process.

That is how you get light emitting diodes and all PN junctions emit light, just usually in infrared spectrum, if you have a forward bias 0.6V, a electron falling that potential must emit photon with energy of 0.6 electron volts, which is hc/0.6eV = 2.07micrometers of wavelength.

That process is reversible. If a photon hits a PN junction it can impart energy to electron thus kicking it out of it’s place in crystal lattice and across the junction, which creates current and generates voltage potential. And there you have it, that’s a basic photovoltaic cell.