The subject matter of the invention is a backup power system configured to be a UPS system, with a customer generation system and with a network monitoring device with a switch topology including a first connection node, that is connected to the customer generation system that is connected to at least one automatic disconnection switch including a first switch said first switch being disposed between the customer generation system and a utility grid, and that is connected to a second switch that is connected to one or several loads, said system including a second connection node that is connected to said second switch connected to said load, that is connected to a third switch disposed between the utility grid and the load and that is connected to a fourth switch to which there is connected a standalone inverter with a storage device, and said system including a third connection node, connecting said first switch and said third switch to said utility grid, said customer generation system supplying an AC voltage that can be added to the circuit, in parallel to said utility grid, the grid monitoring device for opening said first switch being provided upon a failure of the utility grid.