A Grid Connected system is connected to a large independent grid (typically the public electricity grid) and feeds excess power into the grid. In the case of Grid connected rooftop PV systems, the electricity demand of the building is met by the PV System. Only the excess is fed into the grid when there is an excess. The feeding of electricity into the grid requires the transformation of DC into AC by a special, grid-controlled inverter. Solar Grid-Tied systems use PV panels to generate DC power. The DC power goes to a grid interactive (grid-tied) inverter which converts the PV panel DC power to 240 volt AC power that is compatible with the power grid. The power from the PV panels goes (via the grid tie inverter) to supply the user's power needs. If the PV system is generating more power than the user can use, the excess is sent out over the grid to supply others. If the user needs more power than the PV system can supply, then the extra is drawn from the grid as usual. Solar Grid tied systems only work when the grid is up. If the grid power goes out, the grid tie inverter is required to shut downimmediately.