This guide provides information to assist in sizing the array and battery of a stand-alone photovoltaic system. Systems considered in this guide 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 guide is applicable to all stand-alone PV systems where PV is the only charging source, and it covers lead-acid batteries only.