Calculate the likely simultaneous load of essential appliances.
How this calculator works
Battery capacity is based on your selected backup load—not automatically on every appliance. We divide required usable energy by inverter efficiency and usable battery depth, then add a modest reserve.
Multiply that load by your target backup hours.
Adjust for inverter losses, depth of discharge and reserve capacity.
Worked example
A practical planning scenario
An essential load of 2.1 kW for ten hours needs 21 kWh of usable energy. After efficiency, depth-of-discharge and reserve adjustments, a nominal battery tier near 30 kWh may be appropriate.
Frequently asked questions
Why use LiFePO4 assumptions?+
LiFePO4 batteries are common for modern solar storage and allow a relatively high usable depth of discharge. Other chemistries require different assumptions.
Will the battery always last the displayed time?+
Actual runtime changes with appliance behavior, battery age, temperature, inverter losses and state of charge.
Should air conditioners be marked essential?+
Only if you truly require them during outages. Cooling loads can increase battery capacity significantly.