Because of the large space requirements of a PV generator, PV systems are particularly threatened by lightning discharges during thunderstorms. The causes of surges in PV systems are inductive or capacitive voltages deriving from lightning discharges as well as lightning surges and switching operations in the upstream power supply system. Lightning surges in the PV system can damage PV modules and inverters. This can have serious consequences for the operation of the system. Repair costs for the inverter, for example, are very high, and system failure can result in considerable profit cuts for the operator of the plant.