Off-Grid Battery Bank Size Calculator
Calculate the battery bank capacity (kWh and Ah) needed for off-grid solar living based on your daily energy use, days of autonomy, and battery type.
Why Battery Sizing Matters An undersized battery bank leaves you without power during cloudy days; an oversized one wastes money. The goal is to store enough energy to cover your needs during days without sufficient solar charging.
Key Concepts Depth of Discharge (DoD): How much of the battery capacity can be used. Lead-acid: 50% recommended max. Lithium (LiFePO4): 80-90% safely. Nickel-iron: 70-80%. Days of Autonomy: How many sunless days your system must survive alone, typically 1-3 days. Round-Trip Efficiency: Energy lost charging/discharging. Lead-acid ~80%, lithium ~95%.
Bank Capacity Formula Required capacity (kWh) = (Daily use x Days autonomy) / (DoD x efficiency) Then convert to Ah: Ah = kWh x 1000 / System voltage (12V, 24V, or 48V)
Battery Types Flooded lead-acid: Cheapest, needs maintenance, 3-5 year life. AGM: Maintenance-free, moderate cost, 4-6 years. LiFePO4: Most expensive upfront but 10-15 year life and far lighter. Best long-term value for off-grid.