How home backup works
A home battery stores energy from the grid or solar and keeps chosen circuits running when the grid goes down.
Normal day
The house runs on the grid and any solar. The battery can charge from solar or the grid and is held ready for an outage.
During an outage
- A standard grid-tied solar inverter shuts off when the grid goes down (anti-islanding), so solar alone does not keep the lights on. This protects utility workers.
- With a battery-based inverter and a transfer switch or backup gateway, the system disconnects from the grid and powers the backed-up circuits from the battery.
- If solar is set up to work with the battery, it can keep recharging the battery during the day.
- When grid power returns, the system reconnects and goes back to normal.
Whole-home vs critical loads
Some systems back up the whole house; many back up a "critical loads" panel with essentials like the fridge, lights, internet and furnace fan. How long the battery lasts depends on its capacity and what you run. See Power basics for the math.
Home backup systems connect to your electrical panel and usually need a licensed electrician, permits and utility approval.
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