Inverters convert DC into AC. For solar applications, inverters may be divided into two categories: solar-direct, or battery-based. Xantrex makes both types of inverters. Most battery-based inverters are designed to work with a battery bank of a specific nominal voltage - 12V, 24V,or 48V. Larger models often include a battery charging function where the inverter essentially works in reverse to charge the batteries using AC electricity such as that of a generator or the electric grid - these models may be referred to as "inverter-chargers". This is what we normally recommend for off-grid systems and grid-tie system where back-up power is desired. "Solar-direct" inverters are designed for connecting to the electric grid, and do not require batteries at all. these usually operate at much higher DC voltages, and are the most efficient way to convert solar power to usable AC power. In order to be UL listed and approved for grid-connection, the solar-direct type of inverter must shut down in the event of grid (utility) failure. In contrast, battery-based inverters are able to run independently under all circumstances.