Battery Bank Sizing Calculator

A battery bank stores energy from solar panels (or other sources) so you can run your home or system when no charging is available — sizing it correctly means you won't run out of power. Enter your daily energy usage, autonomy days, battery type, and system voltage into the Battery Bank Sizing Calculator to find your required battery capacity in Ah. Secondary outputs include battery bank size (kWh), usable energy storage, and total energy required.

kWh

Your total daily energy consumption in kilowatt-hours

days

Number of days the battery should power your system without solar charging

%

Maximum discharge percentage (50% for lead acid, 80% for lithium recommended)

%

Overall system efficiency including inverter losses

Results

Required Battery Capacity

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Battery Bank Size

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Usable Energy Storage

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Total Energy Required

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Frequently Asked Questions

How much battery storage do I need for my off-grid system?

Battery storage requirements depend on your daily energy usage and desired backup days. Multiply your daily kWh usage by the number of backup days, then account for depth of discharge limits and system inefficiencies.

What's the difference between lead acid and lithium battery sizing?

Lead acid batteries should only be discharged to 50% capacity, requiring roughly double the capacity of lithium batteries which can safely discharge to 80%. Lithium also has higher efficiency and longer lifespan.

How do I calculate my daily energy usage?

List all your appliances with their power ratings in watts, estimate daily usage hours for each, then multiply watts × hours ÷ 1000 to get kWh per day. Add up all appliances for total daily usage.

What does depth of discharge (DoD) mean?

Depth of discharge is how much of the battery's capacity you use before recharging. Limiting DoD to 50% for lead acid and 80% for lithium significantly extends battery life and maintains performance.

How many days of autonomy should I plan for?

Most off-grid systems are designed for 3-5 days of autonomy to handle cloudy weather. Consider your local climate, backup generator availability, and critical vs non-critical loads when choosing autonomy days.

Should I choose 12V, 24V, or 48V for my battery bank?

Higher voltages are more efficient for larger systems. Use 12V for small systems (<1000W), 24V for medium systems (1000-3000W), and 48V for large systems (>3000W) to reduce current and wire losses.

What system efficiency should I use in calculations?

Typical system efficiency ranges from 80-90%, accounting for inverter losses, wiring losses, and battery inefficiencies. Use 85% as a conservative estimate, or 80% for systems with older equipment.