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Solar & battery

Solar Inverter Battery Calculator

Match a hybrid inverter to a battery and the loads it has to carry during an outage.

Your numbers

Result

Runtime on battery 3.1 Hours
Continuous headroom 30.0%
Surge margin at 2x rating 30.0%
Hours to recharge from empty 2.2
Charge rate as a fraction of capacity 0.5 C
The battery runs the load for 3.1 hours and recharges from empty in 2.2 hours of good sun. Continuous headroom is 30.0%.

Three separate limits have to be satisfied and they are often confused: the inverter's continuous rating carries the load, its surge rating starts motors, and the battery's charge rate controls how fast it refills. A large battery on a small inverter still trips when the well pump starts.

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Questions

About this calculator

Why does a big battery not solve a tripping inverter?

Because the inverter is the bottleneck for power, not energy. Capacity determines how long you run; the inverter rating determines what you can run at all.

What limits recharge speed?

Whichever is smaller: the battery's accepted charge rate or what the array can produce at that moment. On a cloudy day the array is usually the limit.

The formula

runtime = usable kWh / continuous load; recharge = usable kWh / the lower of charge rate and array output

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