Home backup power planner
How much battery do you need to ride out an outage? Pick what must keep running, how long outages last where you live, and any solar you have. We'll size every system — including add-on batteries — and show the total cost.
How we calculate
Daily energy = each device's running watts × the hours it draws power. Solar supplies panel watts × sun hours × 75% (real-world losses), capped at each system's solar input limit. The battery must cover the outage's shortfall — and at least half a day's use, since solar can't help at night — divided by 85% inverter efficiency. A system qualifies if its continuous output covers everything running at once, its surge covers the biggest motor starting, and it offers 240V when a device needs it. Add-on batteries are added one at a time up to each system's published expansion limit. Prices are typical current prices; check the retailer before buying.