It's actually straightforward to ensure "one way" flow of power. That's what "islanding" circuits do. They isolate your home when the public utility lines go down by triggering a device that is essentially an electrically controlled switch. It's a unit that connects between your home and the utility company so you can continue to use your solar power/batteries when the public utility is out. If you don't have islanding, the solar inverter cuts off the panels when utilities go down. Both protect workers from encountering lines energized by homes.