Solar Battery Bank Calculator
Size an off-grid battery bank from daily kWh, days of autonomy, voltage, depth of discharge, and inverter efficiency.
Processed locally in your browser — nothing is uploaded.
Solar Battery Bank Calculator
How long the bank must carry the load without sun.
Commonly 12, 24, or 48 V.
Results
- Required bank capacity
- 579 Ah
- Required energy
- 27.78 kWh
- Batteries needed
- 6
600 Ah installed at 100 Ah each.
Batteries in series raise voltage, in parallel raise Ah — the count here is total batteries at the system voltage. Cold temperatures and battery age reduce usable capacity.
About Solar Battery Bank Calculator
Multiply daily consumption by the days of autonomy you want to survive without sun, then inflate it for depth of discharge (about 50% usable for lead-acid, 80–90% for LiFePO4) and inverter losses. The result is the required bank capacity in Ah at your system voltage, plus how many batteries of a given size that takes.
Common uses
- Size batteries for an off-grid cabin that must ride out two cloudy days
- Compare how many lead-acid vs LiFePO4 batteries a load needs
- Check whether an existing bank actually covers your autonomy target
Example
Input
10 kWh/day · 2 days · 48 V · 80% DoD · 90% inverter
Output
≈ 579 Ah → 6 × 100 Ah batteries
Limitations
- Counts batteries at the system voltage — series strings to reach that voltage are up to your wiring plan. Cold weather reduces usable capacity.
Frequently asked questions
What does days of autonomy mean for a battery bank?
It is how many days the bank must carry your loads with no solar input at all — essentially your cloudy-weather buffer. Off-grid designs commonly target 2 to 3 days; multiplying daily consumption by that number is the first step of the sizing.
How many batteries do I need for an off-grid solar system?
Take daily kWh times days of autonomy, divide by depth of discharge and inverter efficiency, convert to Ah at your system voltage, then divide by one battery's Ah. For example, 10 kWh/day for 2 days at 48 V with 80% DoD and 90% efficiency needs about 579 Ah — six 100 Ah batteries.
Why can I only use 50% of a lead-acid battery?
Regularly discharging lead-acid below about half its capacity dramatically shortens its cycle life, so designs treat only 50% as usable. LiFePO4 tolerates 80 to 90% depth of discharge, which is why a lithium bank can be nominally much smaller for the same load.
Do my energy usage numbers get uploaded when I use this?
No. All the bank sizing runs in your browser — your consumption, voltage, and battery details are never transmitted or stored.
Does the calculator handle batteries wired in series?
No — it counts batteries as capacity at the system voltage you chose. How you combine 12 V units in series strings to reach 24 V or 48 V, and parallel strings for capacity, is left to your wiring plan.