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Battery bank size calculator

Battery Ah and kWh for a daily load, days of backup and system voltage.

Try the circuit in the labBuild it on the simulator's bench and measure it.

How it is worked out

Battery Wh = daily Wh × days ÷ inverter efficiency ÷ depth of discharge, then Ah = Wh ÷ system voltage.

Example: 3,000 Wh a day for one day through a 90 % inverter on LiFePO4 used to 90 %: 3000 ÷ 0.9 ÷ 0.9 = 3,704 Wh. At 48 V that is 77 Ah, so a 48 V 100 Ah pack (5.1 kWh) does it with room to spare. Lead-acid should only be used to about 50 % to last, so the same load needs about 6,700 Wh of lead-acid.

Days of backup is for cloudy days: off-grid, 1.5 to 2 days is common; for brownout backup, one night is usually enough.

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