Photovoltaic effect (solar cell)

The photovoltaic effect is how sunlight is turned straight into electricity, with no moving parts and no fuel. A solar cell is a big, flat semiconductor diode: when a photon dives in and gives up its energy, it frees an electron, and the diode's built-in junction field acts like a one-way slide, pushing freed electrons to one side and holes to the other. That separation of charge is a voltage, and wiring the two sides through a load lets the current do useful work. Sunlight in, current out — a diode quietly generating its own power.

A single silicon cell makes only about 0.5–0.6 V, so panels wire dozens in series to reach useful voltages, then strings of panels in series and parallel for kilowatts. Real cells convert roughly 20–25% of incident sunlight to electricity (the rest is lost as heat or to photons too weak or too strong to use). It's the same physics as a photodiode, just scaled up and optimised to harvest energy rather than read signals — which is why a solar panel and a camera's light sensor are cousins.