Solar & battery
Solar Battery Backup Time Calculator
How long backup lasts through an outage, load by load, with and without sun.
Result
Enter usable capacity, not nameplate, or the answer will be a third too generous. Averages matter more than peaks here: a fridge rated 400 W draws that only while the compressor runs, so its daily average is far lower.
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About this calculator
Which loads should be on backup?
Refrigeration, lighting, communications, and any pump that keeps water out or in. Heating and cooling are usually excluded because they empty a home battery quickly.
Will my solar work in an outage?
Only with the right equipment. A standard grid-tied inverter shuts down when the grid fails, for the safety of line workers. Producing power during an outage needs a hybrid inverter or a secure backup circuit.
The formula
hours = usable kWh x 1000 / total load in watts
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