CalculatorStorage

Battery backup time

How long a home battery runs your house in an outage, and how much solar refills it in a day.

BatteryEnergy, kWhUnitsAverage home load, kW

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Backup time

from a full charge

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Total energy

all units

Solar array to refill it in one day

City	December	June

Array size that refills the battery from empty in one average day · NLR (formerly NREL) PVWatts v8 typical-year weather · roof mount, 20° tilt, facing south, 14% system losses

How it is calculated

Backup timeEnergy × units ÷ average load. A typical home averages 1–2 kW; air conditioning and EV charging use much more.
Usable vs nameplateBattery pages show usable energy from the datasheet when it exists; otherwise the CEC nameplate.
RefillEnergy ÷ the daily output of 1 kW of panels in that city in December and June.