Measuring the mains frequency - notes and ideas

[@Magic-Smoke]

You could also poll the inverter parameters to see if import/export switching is affecting frequency?

[@m1geo]

Absolutely. I expect the inverter should be either lagging or leading the line phase, so control import/export direction. But not super sure.

[@aaronbrown1988]

How resilient is the measurement to things like Power Line networking?

[@m1geo]

Should be pretty good. That's partly the reason for the filtering. To remove higher frequency stuff like PLT and SMPS transients.