An energy supply system for supplying electrical energy to a building, comprising a grid connector unit for providing a connection to an external power grid, a load connector unit for connecting to a building power grid, a conductor loop for electrically connecting the grid connector unit to the load connector unit, an energy storage device connected to the conductor loop, and a disconnector placed in the conductor loop for, upon activation of the disconnector, disconnecting the electrical connection between the grid connector unit and the load connector unit, whereby the energy storage device is connected to the conductor loop via a discharging line such that electrical energy stored in the energy storage device may be discharged through part of the conductor loop to the load connector unit when the disconnector is activated.