I’m shopping for a home power backup system. How much battery capacity do I need to power an entire house during a blackout?

I think that will depend on how much energy you want to be using during a blackout. If you want to get through it without any changes to your lifestyle, then you can check your last couple of energy bills to get an average of how much power you use per day.

Typically, an average U.S. household might use around 30 kWh (kilowatt-hours) each day. To cover this for 24 hours, you would need a battery system with at least that much capacity. You can get that much capacity from systems like the Delta Pro Ultra, as this website shows.

That said, there are three good things to consider here. First, blackouts that last more than a few hours are rare, so you can probably get away with getting just 12 hours or 6 hours of backup capacity. Second, if you have power generators, that can supplement the battery capacity to help keep the lights on longer. And third, you can always cut down on energy use during a blackout to make batteries last longer. With power rationing, you can likely get your house down to 10kWh per day, or even less.