Battery based systems store the solar energy generated during the day, in batteries, for later usage. An intelligent inverter blends solar power generated with the grid power to supply the loads. Solar power is always preferred over grid power thereby reducing the overall grid usage. In the event of a power failure, solar power (via the battery bank) takes over completely.
Such systems can essentially be either a simple backup system for power cuts or a completely off the grid system where all your energy needs are met by solar power.