I found this that explains a lot. We're on the right track of thinking
about what happens and that it's kind of a paradox as to how to detect
the loss of the "grid". They call this problem "islanding". This
talks about the ways they detect it, it's complicated and even includes
active action by inverters to deliberately try to destabilize the
grid so that it goes off kilter and all the other inverters can more
quickly detect it. It looks like they use voltage changes, freq changes
and power factor changes as possible parts of the algorithms and
that it's not a trivial problem. I think this gear is more for a larger
commercial array, but the same principles should apply to all inverters.


https://www.solectria.com/blog/anti-...-pv-inverters/

that is interesting

it is also what makes the frustrating situation for people that spent a lot of money for a solar system, and they still have no electricity when the grid is down, even when the sun is out.

m