Solar battery calculator
Size the battery bank of an off-grid or hybrid solar system and see how many batteries to wire in series and parallel.
How it is calculated
kWh = daily use × days / (DoD × efficiency)
Ah = kWh × 1000 / bank voltage
Depth of discharge (DoD) is the share of capacity you can use without damaging the battery: 80–90 % for LiFePO4 lithium and about 50 % for lead-acid.
Wiring in series adds voltage; in parallel, capacity. For banks above 2–3 kWh, 48 V is preferable: current is lower and cables thinner.
Frequently asked questions
How many kWh of battery does a house need?
It depends on night-time use. To cover the night in an average home, 10–15 kWh of usable capacity is typical in the US.
Lithium or lead-acid?
LiFePO4 costs more but gives more usable capacity, lasts 3–5 times as many cycles and needs no maintenance.
Why use 48 V?
For the same power, current at 48 V is a quarter of that at 12 V, reducing losses and cable size.