The main principle of photovoltaic power generation is the photoelectric effect of semiconductors. When a photon shines on a metal, its energy can be fully absorbed by a certain electron in the metal. The energy absorbed by the electron is large enough to overcome the internal gravity of the metal and do work, escape from the metal surface and become a photoelectron. Silicon atoms have 4 outer electrons. If an atom with 5 outer electrons, such as phosphorus atom, is doped into pure silicon, it becomes an N-type semiconductor; If atoms with three outer electrons, such as boron atoms, are doped into pure silicon, a P-type semiconductor is formed. When P-type and N-type are combined, the contact surface forms a potential difference, becoming a solar cell. When sunlight shines on the P-N junction, the current flows from the P-type side to the N-type side, forming a current. Usually, the collected light energy is converted into electrical energy for storage, and electrical energy is released when needed. Typical applications include solar street lights and solar power generation.