AC line voltage variation is mostly about local generation, local consumption , and the resistance in the run from the inverter to the pole transformer.
Low local consumption on a cool sunny day, will produce higher line voltage. Add some local usage, and the line voltage will go down.
This is becoming a problem with neighborhoods with lots of solar, nobody really cares/notices with low line voltage, your fridge does not fault out, but the safeguards in GT inverters, when the line voltage goes up, they start shutting down as individual voltage sense goes over the threshold.