Solar Battery Bank Calculator
Size off-grid, marine, and RV battery storage in Amp-Hours and kWh factoring in depth of discharge, system voltage, and autonomy days.
How to Size a Solar Battery Bank
Sizing a battery bank requires balancing daily power consumption with battery chemistry limitations. To prevent destroying batteries, you must never discharge them below their rated Depth of Discharge (DoD).
Battery Bank Capacity Formula
Capacity (Ah) = [Daily Wh × Autonomy Days] / [System Voltage × DoD × Inverter Eff]
Lead-Acid (AGM/Gel) vs. LiFePO4 Lithium
While Lead-Acid batteries appear cheaper upfront, discharging them beyond 50% cuts their lifespan from 1,200 cycles to under 300 cycles. Lithium Iron Phosphate (LiFePO4) can be safely discharged to 85–90% for 3,000 to 5,000+ cycles, effectively cutting required bank physical weight and size in half.
Frequently Asked Questions
Should I build a 12V, 24V, or 48V solar battery system?
For inverter loads under 1,500W, 12V is fine. For 1,500W to 3,000W, 24V is recommended. For loads over 3,000W (whole home off-grid), 48V is strongly recommended to keep amperage low and wire sizes manageable.
What does "Days of Autonomy" mean?
Days of autonomy represents how many days your system can run strictly from battery power with zero solar panel generation (such as during heavy rain or snowstorms).
Why do we factor in inverter efficiency?
DC to AC inverters consume power converting 12V/24V/48V DC into 120V/240V AC. Quality pure sine wave inverters operate at 88% to 94% efficiency, meaning 6% to 12% of battery energy is lost as heat.