Provided in this recommended practice is information to assist in sizing the array and battery of a stand-alone photovoltaic (PV) system. Systems considered in this recommended practice consist of PV as the only power source and a battery for energy storage. These systems also commonly employ controls to protect the battery from being over- or under-charged and may employ a power conversion subsystem (inverter or converter). This recommended practice is applicable to all stand-alone PV systems where PV is the only charging source. This recommended practice does not include PV hybrid systems nor grid-connected systems. This recommended practice covers lead-acid batteries only; nickel-cadmium and other battery types are not included. This recommended practice does not include the sizing of the system controller, inverter, wiring, or other system components.