Solar Panel Physics — From Photons to Power
A solar panel is Einstein's Nobel-prize physics manufactured by the square kilometer: photons knock electrons loose in silicon, and clever engineering herds them into a current. The efficiency limits are pure quantum mechanics.
The photovoltaic effect
When a photon with enough energy strikes silicon, it frees an electron from its atom — the photoelectric effect in a solid. A built-in electric field at the p-n junction sweeps freed electrons one way and holes the other, producing direct current.
Band gaps and wasted photons
Silicon's band gap is 1.1 eV: photons below it pass through uselessly, while photons far above it waste their excess energy as heat. This single number explains why one material can never capture the whole solar spectrum.
The Shockley-Queisser limit
Quantum mechanics and thermodynamics together cap a single-junction cell at about 33% efficiency under standard sunlight. Real silicon panels reach ~22-26%; multi-junction cells stack materials with different band gaps to climb past the single-junction limit.
From DC to your outlets
Panels produce direct current; an inverter converts it to grid-compatible alternating current, tracking the maximum power point as clouds and temperature shift the panel's current-voltage curve throughout the day.
Try this yourself
- Shade one cell of a small solar garden light and watch the output collapse — cells in series are only as strong as the weakest.
- Tilt a panel toward and away from the sun; the power follows the cosine of the angle, just like the flux law predicts.
- Feel a panel in full sun: the warmth is the wasted excess photon energy becoming heat.