Master battery bank sizing for off-grid solar. Step-by-step method covering daily consumption, autonomy days, DoD, efficiency losses, and practical examples.
A correctly sized battery bank is the difference between reliable off-grid power and frustrating blackouts. This guide provides a clear, repeatable method for sizing your battery bank based on real-world conditions in the Middle East and Africa.
The 5-Step Sizing Method
Step 1: Daily Energy Consumption
Add up all appliance watt-hours per day. Include a 25% margin for system losses. Example: 5,000 Wh x 1.25 = 6,250 Wh (6.25 kWh).
Step 2: Days of Autonomy
How many days should your batteries last without solar charging?
| Climate | Recommended Autonomy |
|---|---|
| Gulf (UAE, Saudi, Oman) | 1.5-2 days |
| North Africa (Egypt, Morocco) | 2-2.5 days |
| Sub-Saharan Africa (rainy season) | 2.5-3 days |
| East Africa (Kenya, Tanzania) | 2 days |
6.25 kWh x 2 = 12.5 kWh required storage.
Step 3: Depth of Discharge
LiFePO4: 80% DoD. GEL: 50% DoD.
LiFePO4: 12.5 / 0.80 = 15.6 kWh. GEL: 12.5 / 0.50 = 25.0 kWh.
Step 4: Temperature Derating
In hot climates, add 15% to account for heat-related capacity loss.
LiFePO4: 15.6 x 1.15 = 18.0 kWh. GEL: 25.0 x 1.15 = 28.8 kWh.
Step 5: Convert to Ah
Ah = kWh x 1,000 / system voltage.
LiFePO4 at 48V: 18,000 / 48 = 375 Ah. GEL at 48V: 28,800 / 48 = 600 Ah.
Quick Reference Table
| Daily Use | LiFePO4 (48V) | GEL (48V) |
|---|---|---|
| 3 kWh | 200 Ah (9.6 kWh) | 345 Ah (16.6 kWh) |
| 5 kWh | 375 Ah (18 kWh) | 600 Ah (28.8 kWh) |
| 10 kWh | 720 Ah (34.6 kWh) | 1,150 Ah (55.2 kWh) |
| 15 kWh | 1,080 Ah (51.8 kWh) | 1,725 Ah (82.8 kWh) |
Why LiFePO4 Wins on Sizing
Notice that the GEL bank needs 1.6x more capacity than LiFePO4 for the same usable energy. This means more batteries, more weight, more space, and more cost — even though individual GEL batteries are cheaper per unit. This is why LiFePO4 is more cost-effective overall for off-grid systems.
Common Sizing Mistakes
- Forgetting system losses (25% margin)
- Only sizing for 1 day of autonomy (too risky)
- Ignoring temperature derating in hot climates
- Confusing rated capacity with usable capacity
- Not accounting for future load growth
Frequently Asked Questions
How big should my battery bank be for a 5kWh daily use?
Why do I need 2 days of autonomy?
Can I add more batteries later to expand my bank?
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