A grid connected system is connected to a large independent grid (typically the public electricity grid) and feeds power in to the grid. This is a form of decentralized electricity generation. In the case of residential or building mounted grid connected PV systems, the electricity demand of the building is met by the PV system. Only the excess is fed in to the grid when there is an excess. The feeding of electricity in to the grid requires the transformation of DC into AC by a special,grid-controlled inverter.