Battery Bank Sizing Calculator
Size your off-grid or backup battery bank based on daily energy consumption, autonomy days, depth of discharge, and system voltage.
Results
What is it?
Battery bank sizing determines how much battery storage capacity you need to power your loads for a specified number of days without solar input. The calculation accounts for depth of discharge (to protect battery longevity) and inverter efficiency losses. LiFePO4 batteries can be discharged to 80-100% DoD; lead-acid batteries should not exceed 50% DoD.
How to use
1. Enter your average daily energy consumption in kWh (check your electricity bill or add up appliance wattages x hours). 2. Enter how many days of autonomy you want (1-3 days is typical for solar backup). 3. Enter the depth of discharge appropriate for your battery chemistry. 4. Select your system voltage (48V is most efficient for larger systems). 5. Enter inverter efficiency (typically 90-97%).
Example scenario
Daily consumption: 5 kWh. 2 days autonomy. LiFePO4 batteries at 80% DoD. 24V system. 95% inverter efficiency. Required capacity = (5 x 2) / 0.80 / 0.95 = 13.2 kWh. In amp-hours at 24V: 13,200 / 24 = 550 Ah. You would need approximately 6 x 100 Ah batteries in a 24V configuration.
Pro tip
Always oversize your battery bank by 20-25% to account for temperature derating (batteries lose capacity in cold weather) and ageing. LiFePO4 batteries are the best long-term investment: they last 2,000-6,000 cycles vs. 300-500 for lead-acid. At a 10-year horizon, LiFePO4 total cost per kWh is often lower despite higher upfront cost.