Solar Street Light Battery Autonomy: How Many Rainy Days Can Your System Handle?
Battery autonomy — the number of consecutive cloudy days a solar street light can operate without sunshine — is the most critical design parameter for African installations. Getting it wrong means lights going dark during the rainy season.
Understanding Days of Autonomy
Days of autonomy (DoA) is defined as the number of consecutive days a solar street light can operate at full capacity without any solar charging input. For African installations, the recommended DoA varies by region: 3 days for most of Sub-Saharan Africa, 5 days for the Congo Basin and coastal West Africa (highest rainfall), and 2 days for the Sahel and Southern Africa (lower rainfall variability).
Battery Sizing Formula
The required battery capacity (in Wh) = LED wattage × operating hours per night × days of autonomy ÷ depth of discharge (DoD). For a 60W LED operating 12 hours/night with 3 days autonomy and 80% DoD (LiFePO4): 60W × 12h × 3 days ÷ 0.80 = 2,700Wh. This requires a minimum battery capacity of 2.7kWh.
| LED Wattage | Operating Hours | 3-Day Autonomy (LiFePO4) | 5-Day Autonomy (LiFePO4) |
|---|---|---|---|
| 30W | 12h | 1,350Wh | 2,250Wh |
| 60W | 12h | 2,700Wh | 4,500Wh |
| 100W | 12h | 4,500Wh | 7,500Wh |
LiFePO4 vs Lead-Acid for Autonomy
LiFePO4 batteries allow 80% DoD vs 50% for lead-acid, meaning you need 37.5% less battery capacity for the same autonomy. Combined with a 6,000+ cycle life vs 500–800 cycles for lead-acid, LiFePO4 is the only viable choice for solar street lights requiring 5+ years of reliable operation in African conditions.
Calculate Battery Autonomy for Your Project
Share your project location and LED wattage, and our team will calculate the optimal battery capacity for your climate zone.
Get Battery Sizing Calculation