Size a solar battery in kilowatt-hours for the evening load you want to cover.
Nominal capacity must exceed the energy actually needed by both the efficiency and depth-of-discharge factors. Lithium batteries allow 90 per cent depth of discharge against about 50 for lead-acid. Oversizing a battery beyond one day of autonomy rarely pays in a grid-connected home, because the extra capacity cycles too rarely to earn its cost.
Solar Battery Size
Capacity = load ÷ round-trip efficiency × autonomy ÷ depth of discharge
Capacity = load ÷ round-trip efficiency × autonomy ÷ depth of discharge Nominal capacity must exceed the energy actually needed by both the efficiency and depth-of-discharge factors. Lithium batteries allow 90 per cent depth of discharge against about 50 for lead-acid.
Oversizing a battery beyond one day of autonomy rarely pays in a grid-connected home, because the extra capacity cycles too rarely to earn its cost.
This calculator takes 4 inputs: Energy needed outside generation hours, Usable depth of discharge, Round-trip efficiency, Days of autonomy wanted. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.