I've got rooftop solar hooked to the grid. If the grid goes down, the inverter disconnects the panels. It's a safety measure to prevent electrocuting anybody working on the wires.

The actual amount of power returned to the grid is bupkis. The panels offset what the house uses on an annual basis, but there's not much leftover.

EDIT: I don't actually own the panels. I got them as part of a PPA. To be able to legally run the house directly off the panels, I would be looking at ~$40k to buy the system from the utility.