PV systems that connect to the utility grid are called grid-tie systems. There are two types: interactive systems and battery-backed systems. Interactive systems do not include batteries, while battery-backed systems do. If the electric grid is powered up, these two systems operate in the same way. They both supply loads with a combination of PV power and utility power. They also export power to the grid when the PV array produces more power than local loads require.

The operation of interactive and battery-backed systems differ when the electric grid goes down. A battery-backed system is able to supply power to critical loads from the batteries in the absence of utility power. An interactive system, on the other hand, does not supply power to the loads when there is no utility power. The reason that interactive systems, which do not have battery backup, stop supplying loads with grid power is the anti-islanding requirement imposed by all utilities. This requirement dictates that the inverter must not apply power to the grid while it is down. Since the output connections of an interactive inverter connect to both the loads and the grid, the loads also lose power while the inverter’s output is disconnected.