Stand-alone PV systems are used in areas that are not easily accessible or have no access to an electric grid. A stand-alone system is independent of the electricity grid, with the energy produced normally being stored in a deep cycle solar batteries. A typical stand-alone system would consist of a PV module or modules, batter­ies, and a charge controller. An inverter may also be included in the system to convert the direct current generated by the PV modules to the alternating cur­rent form required by normal appliances.

These systems can provide reliable power for commu­nication systems, especially in remote locations, away from the utility grid. Examples include communication relay towers, travelers’ informa­tion transmitters, cellular telephone transmitters, radio relay stations, emergency call units, solar street lighting systems, and military communication facilities. Obviously, these systems are stand-alone units in which PV-charged batteries provide a stable DC voltage that meets the vary­ing current demand. Practice has shown that such PV power systems can operate reliably for a long time with little maintenance.