Solar Battery Sizing Guide: How Much Storage Do You Need?
Sizing your battery correctly is the difference between a system that works perfectly and one that leaves you in the dark. This guide provides a step-by-step method to calculate exactly how much battery capacity you need.
🎯 The Basic Formula
Battery Capacity (kWh) = Daily Load (kWh) × Autonomy Days ÷ DOD
DOD = Depth of Discharge (use 0.9 for LiFePO4, 0.5 for lead-acid)
Step 1: Calculate Your Daily Load
List every electrical device you want to power during a grid outage. Multiply watts × hours of daily use.
| Appliance | Power (W) | Hours/Day | Daily kWh |
|---|---|---|---|
| LED Lights (10 bulbs) | 100 | 5 | 0.5 |
| Refrigerator | 150 | 8 (compressor) | 1.2 |
| TV + Router | 150 | 4 | 0.6 |
| Laptop/Phone Charging | 100 | 4 | 0.4 |
| Ceiling Fan (2x) | 150 | 8 | 1.2 |
| Water Pump (0.5 HP) | 375 | 1 | 0.375 |
| Total Daily Load | 4.275 kWh | ||
Step 2: Choose Autonomy (Backup Days)
How many days of backup do you need without solar recharging?
- Grid-tied with net metering: 0.5-1 day (short outages only)
- Grid-tied with frequent outages: 1-2 days
- Off-grid with generator backup: 1-2 days
- Off-grid, no generator: 2-3 days (or more, depends on weather)
Step 3: Apply Depth of Discharge (DOD)
| Battery Type | Recommended DOD | Usable from 10kWh |
|---|---|---|
| LiFePO4 | 90% | 9 kWh |
| Lead-Acid | 50% | 5 kWh |
Real-World Sizing Examples
Example 1: Small Home (Africa/Middle East)
- Daily load: 5 kWh
- Backup needed: 1 day (grid available, but unreliable)
- Battery type: LiFePO4 (DOD 90%)
- Required battery: 5 × 1 ÷ 0.9 = 5.5 kWh → Choose 5kWh wall-mounted battery
- Recommended: 1 × Wall-Mounted 5kWh LiFePO4
Example 2: Off-Grid Cabin
- Daily load: 3 kWh
- Backup needed: 2 days (no generator, cloudy season)
- Battery type: LiFePO4 (DOD 90%)
- Required battery: 3 × 2 ÷ 0.9 = 6.7 kWh → Choose 10kWh
- Recommended: 1 × Wall-Mounted 10kWh LiFePO4
Example 3: Small Business (Shop/Bakery)
- Daily load: 15 kWh
- Backup needed: 1 day
- Battery type: LiFePO4 stackable
- Required battery: 15 × 1 ÷ 0.9 = 16.7 kWh → Choose 15-20kWh system
- Recommended: 1 × Stackable 15kWh or 2 × Wall-Mounted 10kWh
Step 4: Match with Solar Array
Your solar panels should produce 1.2-1.5× your daily load to ensure the battery can be fully recharged:
- 5kWh daily load → Minimum 1.5kW solar array (assuming 4 peak sun hours)
- 10kWh daily load → Minimum 3kW solar array
- 15kWh daily load → Minimum 4.5kW solar array
Step 5: Inverter Sizing
Your inverter must handle the peak power (all devices starting simultaneously), not just average power:
- Total running watts × 1.5 = minimum inverter size (account for surge)
- Example: 2,000W running load needs at least 3,000W (3kW) inverter
- Motor loads (pumps, compressors) may need 3-5× their rated power for startup
Need help sizing your system?
Tell us your daily load and backup requirements — we'll recommend the right battery and inverter combination.
Get Free Sizing Advice →Last updated: June 2026. Calculations are estimates. Actual performance depends on installation, usage patterns, temperature, and system design. Always consult a qualified solar installer.