Sunlight is converted to DC (direct current) electricity using the silicon and other chemical elements within the solar panels (PV array). The DC current runs down the electrical cabling to the inverter. The inverter transfers the current from DC to 240 volt AC (alternating current)- so that it is suitable for use in your home. Any unused energy is sold back to the grid through your meter.  No energy is stored. The only way to store energy is through a battery. This is an expensive option and is generally only used where mains electricity is not available.

How Electricity is Generated

A solar cell contains two layers of semiconductor material generally composed of silicon crystals. On its own, crystallized silicon is not a great conductor of electricity, but a process called doping adds impurities to the silicon to improve its conductivity. The bottom layer of the PV cell is usually doped with boron and bonds with silicon to facilitate a positive charge (P). The top layer is doped with phosphorus and bonds with the silicon to facilitate a negative charge (N).

Close up of a polycrystalline panel, showing the wiring

The surface between the resulting “P-type” and “N-type” semiconductors is called the “P-N” junction. Electron movement at this surface produces an electric field that only allows electrons to flow from the p-type layer to the n-type layer.

When sunlight enters the solar 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 (wiring) 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 are the external circuit. The electrons flowing through this circuit providing  a supply of electricity.

Each solar cell is around 10 cm square and generates very little power (less than two watts). The solar cells are often grouped together as modules. Modules can then be grouped into larger panels encased in glass (usually) to provide protection from the weather, and these panels, in turn, are either used as separate units or grouped into even larger arrays.

This extract is taken from the Union of Concerned Scientists’ website.