How does a solar cell turn sunlight into electricity?

The sun's light (and all light) contains energy. Usually, when light hits an object the energy turns into heat, like the warmth you feel while sitting in the sun. But when light hits certain materials the energy turns into an electrical current instead, which we can then harness for power. Solar technology uses large crystals made out of silicon, which produces an electrical current when struck by light. Silicon can do this because the electrons in the crystal get up and move when exposed to light instead of just vibrating in place to make heat. The silicon turns a good portion of light energy into electricity.

The most important components of a PV cell are two layers of semiconductor material generally composed of silicon crystals. On its own, crystallized silicon is not a very good conductor of electricity, but when impurities are intentionally added—a process called doping—the stage is set for creating an electric current. The bottom layer of the PV cell is usually doped with boron, which bonds with the silicon to facilitate a positive charge (P). The top layer is doped with phosphorus, which bonds with the silicon to facilitate a negative charge (N).

When sunlight enters the cell, its energy knocks electrons loose in both layers. Because of the opposite charges of the layers, the electrons want to flow from the n-type layer to the p-type layer, but the electric field at the P-N junction prevents this from happening. The presence of an external circuit, however, provides the necessary path for electrons in the n-type layer to travel to the p-type layer. Extremely thin wires running along the top of the n-type layer provide this external circuit, and the electrons flowing through this circuit provide the cell's owner with a supply of electricity.

Most PV systems consist of individual square cells averaging about six inches on a side. Alone, each cell generates very little power (approximately four watts), so they are assembled together panels encased in glass and plastic to provide protection from the weather. These panels are either used as separate units or grouped into even larger arrays to form a solar power (PV) system.