Why don't solar cells eventually run down as electrochemical cells do?

Answer 1

In the case of electrochemical cells, the energy is coming from the reactions inside the cell- the chemicals inside have some stored energy, and as the cell is used, that energy is used up and they are converted into different chemicals with less energy, until the cell runs out.

Solar cells get their energy from the sun- sunlight has energy, and what the solar cell does is convert that light energy into electrical energy. So it doesn't use any energy of its own (it does lose electrons, but more electrons come in from the circuit so it never runs out). So as long as a solar cell is exposed to light, it won't run down.

In the long term, the sunlight will start to degrade the solar cell so it will eventually stop working, but not because it runs out of energy.