The small "Stand-Alone" system is an excellent system for providing electricity economically. These systems are used primarily for RV power, lighting, cabins, backup and portable power systems. The size of the photovoltaic array (number of solar panels) and battery will depend upon individual power requirements. The solar panels charge the battery during daylight hours and the battery supplies power to the inverter as needed. The inverter changes the 12 volt batteries DC power into 120 volt AC power, which is the most useful type of current for most applications. The charge controller terminates the charging when the battery reaches full charge, to keep the batteries from "gassing-out", which prolongs battery longevity.