Geomagnetic effects happen on scales measured in tens or hundreds of miles/km. There is no particular threat to rooftop solar unless the event is on a scale comparable to a nearby EMP burst from a nuke attack. In which case you probably aren't too concerned about your solar installation as a first order priority.

It also isn't correct to assume that the grid is wholly unprotected. Substations have extensive protection in the form of interrupters.