Battery Storage Sizing Calculator Formula
Understand the math behind the battery storage sizing calculator. Each variable explained with a worked example.
Formulas Used
Required Battery Capacity
required_capacity = energy_needed / (depth_of_discharge / 100) / (round_trip_efficiency / 100)Usable Capacity
usable_capacity = energy_needed / (round_trip_efficiency / 100)Total Energy to Store
total_energy_stored = energy_neededVariables
| Variable | Description | Default |
|---|---|---|
daily_usage_kwh | Daily Energy Usage(kWh) | 30 |
autonomy_days | Days of Autonomy(days) | 2 |
depth_of_discharge | Depth of Discharge(%) | 80 |
round_trip_efficiency | Round-Trip Efficiency(%) | 90 |
energy_needed | Derived value= daily_usage_kwh * autonomy_days | calculated |
How It Works
Sizing Battery Storage for Solar
Battery storage bridges the gap between solar generation and energy use, especially overnight or during cloudy days.
Formula
Required Capacity = (Daily Usage x Autonomy Days) / DoD / Round-Trip Efficiency
Depth of Discharge (DoD) is the fraction of the battery you can actually use without damaging it. Lithium-ion batteries typically allow 80-90% DoD, while lead-acid batteries are limited to 50%.
Worked Example
A home uses 30 kWh/day and wants 2 days of autonomy with 80% DoD and 90% efficiency.
daily_usage_kwh = 30autonomy_days = 2depth_of_discharge = 80round_trip_efficiency = 90
- 01Energy needed = 30 x 2 = 60 kWh
- 02Account for efficiency = 60 / 0.90 = 66.7 kWh usable
- 03Account for DoD = 66.7 / 0.80 = 83.3 kWh total capacity
Ready to run the numbers?
Open Battery Storage Sizing Calculator