Protection for ground-mounted photovoltaic systems

Protection solution for solar parks with central inverter

PV system concepts with central inverters are usually set up with generator junction boxes, so-called DC combiner boxes or DC sub-distribution boards, in the field and a central inverter near the transformer station. The generator junction boxes are usually located on the mounting system of the solar modules, where the respective strings are collected and routed to the central inverter. 

In the event of a direct lightning strike to the air-termination system or metal structure of the support frame, this extensive DC cabling acts as an equipotential bonding conductor between the local earth potential of the module field and the "remote" equipotential surface of the infeed transformer or central inverter. Partial lightning currents flow in the DC cabling with both relatively low and high specific earth resistance. Due to the partial lightning currents to be expected, Type 1 + 2 combined arresters are also required to protect the DC system components in addition to the AC side.

Protection solution for solar parks with string inverter

In contrast to systems with central inverters, partial lightning currents flow on the AC lines in systems with decentralised string inverters. Accordingly, Type 1 + 2 combined arresters must be installed on the AC side of the string inverters and the low-voltage side of the infeed transformer. 

With an appropriately designed earthing system, the string inverters and the module field connected to them form a local equipotential surface so that no lightning currents are to be expected on the DC cabling. Type 2 arresters (e.g. DEHNguard M YPV) are therefore sufficient on the DC side. The communication interfaces are also fitted with suitable surge protective devices.