Battery Storage Sizing Calculator
Determine the required battery storage capacity for a solar system based on daily usage, autonomy days, and depth of discharge.
kWh
days
%
%
Required Battery Capacity
83.3 kWh
Usable Capacity66.7 kWh
Total Energy to Store60 kWh
Required Battery Capacity vs Daily Energy Usage
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%.
Example Calculation
A home uses 30 kWh/day and wants 2 days of autonomy with 80% DoD and 90% efficiency.
- 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