Solar power inverters that send excess solar power back to the grid are (usually) required to shut down if the grid power fails. (This is to protect people working on the power lines.)

The inverter only has two wires connecting it to the switchboard. (Active and Neutral). How does the inverter know if the grid power has failed if it is using those wires to output power?

I suspect that every few seconds the inverter stops outputting power for one cycle and senses the grid voltage.

If that is the case, then why doesn't the back EMF from inductive loads (air-conditioners etc) fill in the missing grid-power for that cycle and make it seem like the grid is still active?

Also, how does it work when everyone in the street has inverters and the grid fails? Wouldn't the inverters just sense that there is still grid power (from the other inverters) and all of them continue operating?


1 Answer 1


The last time I asked this, the answer was that the inverter tries to change the frequency and the grid is so large in comparison that the grid frequency does not move so the inverter senses a difference.

When the grid has disappeared then the frequency is easily changed which means the inverter stops output to prevent issues like islanding.


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