Size a battery bank in amp-hours for a required load, runtime and depth of discharge.
Usable energy is only a fraction of nameplate capacity, because deep discharge shortens battery life sharply. Dividing by both inverter efficiency and depth of discharge gives the nominal capacity that must actually be bought. Lead-acid batteries are normally limited to 50 per cent depth of discharge and lithium to 80 to 90 per cent, which is why the chemistry changes the required capacity so much.
Battery Capacity
Ah = load × hours ÷ (inverter efficiency × depth of discharge × system voltage)
Ah = load × hours ÷ (inverter efficiency × depth of discharge × system voltage) Usable energy is only a fraction of nameplate capacity, because deep discharge shortens battery life sharply. Dividing by both inverter efficiency and depth of discharge gives the nominal capacity that must actually be bought.
Lead-acid batteries are normally limited to 50 per cent depth of discharge and lithium to 80 to 90 per cent, which is why the chemistry changes the required capacity so much.
This calculator takes 5 inputs: Load, Required runtime, System voltage, Usable depth of discharge, Inverter efficiency. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.