What Does This Error Mean?

Fronius State 304 means the grid frequency exceeded the maximum allowed limit (typically above 50.2 Hz in European grids or 60.2 Hz in North American grids). This is a grid fault, not an inverter fault — the Fronius will restart automatically once the grid frequency returns to normal.

Affected Models

Fronius Primo
Fronius Symo
Fronius Galvo
Fronius IG Plus
All Fronius string inverters

Common Causes

Grid overfrequency event — the utility grid frequency rose above the permitted maximum, causing all inverters to disconnect as required by safety standards
Local generator or large capacitor bank connected nearby causing frequency deviation
Faulty Fronius frequency measurement — very rare, but sensor issues can falsely report overfrequency
Inverter frequency trip settings too narrow for local grid conditions

How to Fix It

Wait for automatic restart.

State 304 triggers an automatic protective shutdown — the Fronius will attempt to reconnect once it detects the grid frequency has returned to normal. The reconnect delay is 60 seconds by default — the inverter will resume production automatically without any intervention. A single State 304 event is not cause for concern.
Check for events on the Fronius Solarweb portal.

Log in to solarweb.com and open the Event Log for your system. Filter for State 304 to see how frequently it is occurring and at what times. Frequent State 304 events — especially clustered at the same time of day — indicate a recurring grid frequency issue in your area.
Report repeated State 304 to your electricity network operator.

If State 304 appears more than once or twice a week, the local grid has a frequency stability problem. Contact your electricity distribution network operator (DNO/DSO) and provide the dates and times of the events from your Solarweb event log. Network operators are responsible for maintaining frequency within the legal tolerance band.
Have a solar installer verify the Fronius frequency settings.

Fronius inverters are pre-configured with grid-code-compliant frequency limits for the country of installation. If the settings were changed or the inverter was imported from a different region, the frequency trip points may not match your local grid standard. A licensed installer with Fronius service access can check and correct the frequency settings.
Distinguish from State 103.

Fronius State 103 also relates to frequency — State 103 is a prolonged grid frequency deviation (sustained out-of-range frequency), while State 304 is an instantaneous overfrequency trip. If you see both codes, the grid has a persistent frequency problem rather than brief spikes. Document both codes in your report to the network operator.

When to Call a Professional

Grid overfrequency is a utility infrastructure issue. If State 304 occurs repeatedly and regularly, report it to your electricity network operator. Your solar installer can also review the Fronius frequency settings to ensure they match local grid codes.