Free calculator
Blackout runtime
Pick what must stay on — fridge, furnace, well pump, medical gear — and see hours of backup by battery size and price.
Hours of backup (no sun)
1 × Powerwall 3 · 13.5 kWh36 h
Installed price: about $19,000
2 × Powerwall 3 · 27.0 kWh73 h
Installed price: about $31,000
3 × Powerwall 3 · 40.5 kWh109 h
Installed price: about $43,000
0 h24 h48 h72 h96 h
Typical appliance energy shown — edit any value to match yours. Assumes ~90% of usable capacity and no solar recharging; with panels, sunny days extend runtime. Power output limits (e.g., motor starts for well pumps) are checked on-site.
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