For customers without a battery backup system installed on their home, when the grid goes down, everything in their home losers power (even if they have solar!). This is a common misconception about solar: solar, by itself, will NOT work if the grid is down. Solar inverters must 'see' a stable grid or they must shut down. This regulation is in place to protect electrical workers. If a solar system were to continue to put energy onto the grid, while the grid is down, then electrical workers trying to fix the issue with the grid could potentially be electrocuted by the solar system. This is where a battery backup shines!
Customers with a battery backup system are protected from grid outages because their battery system creates a micro-grid at their home. By strategically locating the home's circuits behind a switch, we can disconnect the home from the grid and then energize those circuits, using the battery backup, without endangering electrical workers trying to restore the grid. As an added benefit, this micro-grid allows the solar system (if installed) to 'see' that stable grid and continue to produce energy when the grid is down.