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.