Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: randomplanck on 23/10/2014 20:29:43
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Let me share a brief exchange that ended up in a dead end on answers.yahoo.com -
If a solar panel converts light into a flow of electrons, what is the source of the electrons?
I understand the mechanism of a solar panel is similar to a light emitting diode in reverse. But I have an easier time visualizing electrons from a power source creating a mass-less particle, but I'm a bit confused about how a mass-less particle (photon) - creates a flow of electrons. (I know small mass but it's still mass). Not an expert on either of course. Hope I'm making sense.
Answer was: Photon absorbed by outer electron - electron now has more energy and escapes the electromagnetic attraction of the atom.
Electron moves, it can also be visualized as a hole moving.
My comment was: So does the outer electron leave? What takes it's place?
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There is not an endless supply of electrons. A solar panel will only provide current if there is a closed circuit (so the electrons just move around in a circle through the circuit). The sunlight just provides an electromotive force by exciting the electrons. The excited electron can then leave the panel to go into the wire, go around the wire, do some work and go back into the panel.
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Fair nuf.
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what is the source of the electrons?
There are a huge number of electrons already existing in the silicon and in the copper of the connecting wires.
The light striking a solar cell does not create any electrons (just as a LED does not destroy any electrons).
In a solar cell, the massless light photon just provides an energy "kick" to get the existing electrons moving around the circuit. (In a LED, the energy of the moving electrons is turned into photons which fly away; the LED forms a resistance in the electrical circuit.)