Battery Bank Calculator
Size a battery bank for off-grid solar systems.
Calculate battery capacity needed based on daily energy usage and backup days.
Battery Bank Size
Battery bank sizing ensures you have enough stored energy to cover your needs.
Required Capacity (Wh) = Daily Usage (Wh) × Backup Days / Depth of Discharge
Battery Ah = Required Capacity (Wh) / System Voltage
Key concepts:
- Depth of Discharge (DoD): How much of the battery you actually use. Lead-acid: 50%. Lithium: 80–90%.
- Backup days: How many days of autonomy you want without sun.
Common battery types:
| Type | DoD | Cycle Life | Cost |
|---|---|---|---|
| Lead-acid (FLA) | 50% | 500–1,000 | Low |
| AGM | 50% | 600–1,200 | Medium |
| Lithium (LiFePO4) | 80% | 2,000–5,000 | High |
System voltages: 12V (small), 24V (medium), 48V (large systems).
Example:
If daily usage is 5,000 Wh, you want 2 days backup, lithium batteries at 80% DoD on a 48V system:
(5000 × 2) / 0.80 = 12,500 Wh → 12,500 / 48 = 260 Ah at 48V