Harold, I cannot speak for NEC requirements. I don't think the code panel itself has come to grips with the various design issues- and the solution to that gets into the basic arrangement of the NEC. Personally, I think ALL sources of power need to be grouped into their own section, and treated as a whole.
As for overcurrent protection, I see that as a design issue. That is, there ought to be overcurrent protection at the point of generation.
Where the two systems come together, there needs to be some way to limit power from 'going the wrong way.' This might very well mean a breaker at that point as well. Otherwise, you have the potential of a fault tripping the feed from one direction - but still have the risk of a backfeed to the fault.
I note that the UL-listed arrays with 'micro-inverters' at the array and a simple circuit to the panel require that you backfeed the power through a breaker into the panel.
