Electricity supply networks are organised hierarchically. There are low-voltage grids, medium-voltage
grids and high-voltage grids. While the latter are designed for overland transmission, the medium-voltage grids supply larger industrial customers and large regional utilities, and the low-voltage grids, as distribution grids, supply end consumers in a regional area. Distribution networks are operated, serviced and maintained by distribution network operators (DSOs). They supply customers directly with three-phase current. The distribution grid operators receive their electricity from the substations, from other distribution grid operators or also from end consumers who feed their electricity into the grid. This can be electricity from regenerative energy, from wind power plants, biogas plants, hydroelectric power plants or photovoltaic plants. Battery banks or neighbourhood storage facilities can also be connected to such a low-voltage distribution network as energy buffers. The exchange of energy with other distribution grid operators ensures the stability and reliability of the supply voltage.