Solar Battery Sizing Calculator | PES Supply
Solar Battery Sizing Calculator
Calculate the battery capacity needed for your solar system. Enter your daily energy usage and backup days to size your battery bank.
Formula
Battery Sizing Reference Table (48V System, 80% DoD)
| Daily Use | 1 Day Backup | 2 Days | 3 Days |
|---|---|---|---|
| 5 kWh/day | 130 Ah | 260 Ah | 391 Ah |
| 10 kWh/day | 260 Ah | 521 Ah | 781 Ah |
| 20 kWh/day | 521 Ah | 1,042 Ah | 1,563 Ah |
| 30 kWh/day | 781 Ah | 1,563 Ah | 2,344 Ah |
| 50 kWh/day | 1,302 Ah | 2,604 Ah | 3,906 Ah |
Battery Bank Design Tips
- Lithium (LiFePO4) batteries typically allow 80-90% DoD
- Lead-acid (AGM/Gel) batteries should only be discharged to 50% DoD
- Higher system voltage (48V) means lower current and smaller wires
- Add 20% capacity margin for system losses and degradation
- Consider temperature derating for cold climate installations
How many batteries do I need for off-grid solar?
For 10 kWh/day with 2 days backup at 48V: you need 521 Ah at 48V. Using 100Ah 48V lithium batteries, that's 6 batteries (600 Ah with safety margin).
What is Depth of Discharge (DoD)?
DoD is how much of the battery capacity you use. Lithium batteries can safely discharge to 80-90%, while lead-acid should stay above 50%. Higher DoD means you need less total capacity.
Should I choose 12V, 24V, or 48V battery system?
For small systems (under 2,400W), 12V is fine. For 2,400-5,000W, use 24V. Above 5,000W, use 48V to keep currents manageable and wire sizes reasonable.