Free Solar Battery Bank Sizing Calculator
Determine total kilowatt-hour capacity, Amp-hours, days of cloud autonomy, and parallel battery string counts for off-grid cabins and RVs.
⚡ Energy Load & System Specs
🔋 Required Bank Capacity
Recommended Tools & Equipment
Tested hardware and components for high reliability
How to Size an Off-Grid Solar Battery Storage Bank
Undersizing an off-grid battery bank leads to chronic deep discharge and premature battery death, while oversizing wastes thousands of dollars. The battery bank must satisfy three primary criteria: daily energy consumption, inverter electrical conversion losses, and days of autonomy (rainy days without solar generation).
LiFePO4 vs Lead-Acid Economics
Traditional AGM or flooded lead-acid batteries can only be safely discharged to 50% Depth of Discharge; discharging lower destroys plate lead chemistry in months. Lithium Iron Phosphate (LiFePO4) easily cycles to 90% DoD for 4,000 to 6,000 cycles, requiring nearly half the physical battery bank capacity.
Why 48V Beats 12V for Cabins
To deliver 3,000 Watts through a 12V inverter requires a massive 250 Amps (demanding huge 4/0 AWG welding cables). At 48V, that exact same 3,000W load requires only 62.5 Amps, dramatically cutting wire costs, voltage drop, and fire hazards.
Frequently Asked Questions
What does 'Days of Autonomy' mean?
Autonomy is the number of consecutive days your battery bank can power all electrical loads without any solar panel recharging (e.g. during a prolonged winter storm or thick cloud cover).
Can I leave lithium batteries in freezing temperatures?
LiFePO4 batteries can discharge in freezing weather (down to -20°C), but they MUST NEVER BE CHARGED below 0°C (32°F) or permanent lithium metal plating will ruin the cells. Always choose batteries with internal low-temperature charging protection or heating pads.
How do I convert between Amp-hours and Watt-hours?
Watt-hours = Amp-hours × System Voltage. For example, a 12V 100Ah battery contains 1,200 Watt-hours (1.2 kWh), whereas a 48V 100Ah battery contains 4,800 Watt-hours (4.8 kWh).