Inverters for PV systems are classified as either stand-alone or interactive in operation. Utility-interactive PV inverters are connected to, and operate in parallel with, the electric utility grid. These inverters interface between the PV array and the utility grid and convert DC output from a PV array to AC power that is consistent and synchronous with the utility grid. Interactive PV systems are interconnected with the utility at the distribution panel or on the supply side of service entrance equipment. In other words, the utility acts as an infinitely large energy storage system that takes the excess energy from the interactive system and supplies extra energy when needed. This allows AC power produced by the PV system to either supply on-site electrical loads or to back-feed power to the grid when the PV system output is greater than the site load demand. At night and during other low solar radiation periods when the electrical loads are greater than the PV system output is taken from stored energy in the utility.