Network and system protection (NS protection) for photovoltaic systems

The safety of the electrical grid can only be guaranteed if the grid voltage and grid frequency remain within prescribed, narrow limits. If these limits are exceeded, there is a risk of damage to electrical devices, but especially to large power plants. To prevent this from happening, they disconnect from the grid. The resulting power grid failure causes a blackout, at least locally. Photovoltaic systems (PV systems) also have to decouple from the grid, as it would be dangerous if an improper grid condition were prolonged by PV systems. It is for this reason that every PV system is required to have an appropriate protective function, which goes by the name of “NS protection”.

Up until 2024, there was much debate as to whether this protective function could be integrated into the inverter or whether there should be an additional external configuration too. Since 2014, and even more explicitly since 2020, the NA/EEA Industry Recommendation of the Association of Swiss Electricity Companies (VSE) has called for PV systems of 30 kVA or over to be equipped with external NS protection. There was much discussion of reasons for and against external NS protection, but no consensus was ever reached. Ultimately, each grid operator makes its own decision as to what applies in its area of the grid.

A large consortium consisting of various network operators, associations and universities from Switzerland, Austria and Germany got together in 2022 to find a joint solution to this issue.

Inverters do not require external NS protection

In June 2024, the project consortium came to the consensus that the disadvantages of external NS protection outweigh the advantages. They noted the following in particular:

• The fact that external NS protection offers no added value for any realistic and relevant failure scenario.
• The high cost of external NA protection.
• The high level of functionality and safety already built into every inverter.
• By adding additional complexity to the system, external NS protection renders it more susceptible to malfunction during commissioning and operation.

Updating the industry documents

The project members, who are also members of the relevant VSE expert committee that drafts the VSE’s NA/EEA Industry Recommendation, will incorporate the findings from the project into the new version, which is expected to be published in early 2025.

But what applies in the meantime? This project has no influence on the legal situation: the distribution system operator stipulates whether or not external NS protection is required. Some grid operators are already doing without NS protection, while others continue to adhere strictly to the current VSE Industry Recommendation. Once the new Industry Recommendation is published, it can be assumed that external NS protection will no longer be installed.