Size an off-grid battery bank in amp-hours for the autonomy required.
Off-grid banks need several days of autonomy because consecutive cloudy days are common. Cold temperatures reduce available capacity, which is why an unheated battery room needs derating. Lead-acid banks are limited to about 50 per cent depth of discharge, so they must be roughly twice the size of a lithium bank for the same usable energy.
Battery Bank Size
Ah = daily draw × autonomy ÷ (depth of discharge × temperature derate)
Ah = daily draw × autonomy ÷ (depth of discharge × temperature derate) Off-grid banks need several days of autonomy because consecutive cloudy days are common. Cold temperatures reduce available capacity, which is why an unheated battery room needs derating.
Lead-acid banks are limited to about 50 per cent depth of discharge, so they must be roughly twice the size of a lithium bank for the same usable energy.
This calculator takes 5 inputs: Daily energy consumption, System voltage, Days of autonomy, Depth of discharge, Derating for low temperature. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.