I got a phone call from co-op asking if I had solar, since my usage had basically gone down to zero. I confessed I did, but explained that the system was isolated from the grid, connected like a backup generator. Guy from the co-op said that's fine, but I couldn't connect an inverter to the grid at all under any circumstances (even if no backfeed) without jumping through all their grid-tie rules. Engineered drawings, state inspection, the whole 9 yards. He said they'd want to come inspect my interlock used to isolate the system, but haven't followed up after all this time.
In my location, with wood heating, 95% of the winter is pretty easily done with off-grid solar. Gotta fill that last gap with diesel genset, or fall back on the grid. I pretended the grid wasn't there, but nearly failed, since the diesel generator was needed when temperatures were close to 0ºF, and the fuel had gelled. I find summer off-grid is actually more difficult than winter, though, with A/C units running overnight...