How do I size a solar battery bank?

Multiply daily energy use by autonomy days, then divide by allowable depth of discharge and system efficiency. Convert the result into Ah using battery bank voltage.

Why does depth of discharge matter?

Depth of discharge limits how much of the battery capacity should be used. Lower usable DoD means a larger battery bank is required.

Solar Battery Bank Calculator | Off-Grid Battery Size

Solar Battery Bank Calculator

Calculate the required battery bank size for solar, off-grid and backup systems in Wh, kWh and Ah.

🔋 Field Rule: Battery size depends on daily load, autonomy days, battery voltage, depth of discharge and efficiency. Build the full solar workflow with the Solar Panel Output Calculator, Solar Panel Series/Parallel Calculator, Solar String Sizing Calculator and MPPT Charge Controller Calculator.

🔋 Load → Battery Bank → Backup Autonomy

Daily Energy Load

Autonomy Days

Battery Bank Voltage

Depth of Discharge

System Efficiency

Safety Margin

Battery Type

Inverter Load Optional

Peak Runtime Estimate

For lithium batteries, usable DoD is often higher. For lead-acid batteries, practical DoD is usually lower to improve life. Always confirm with the battery datasheet.

Presets:small cabinhome backuplead-acid bank

Required Capacity

Single Battery Voltage

Single Battery Capacity

Target Bank Voltage

Usable DoD

📐 Formula Reference

Energy Required

Required Wh = daily load × autonomy days ÷ DoD ÷ efficiency

Ah Capacity

Battery Ah = required Wh ÷ battery bank voltage

Battery Energy

Battery Wh = voltage × Ah
Battery kWh = Wh ÷ 1000

Battery Count

Series batteries = target voltage ÷ battery voltage
Parallel strings = required kWh ÷ string kWh

📋 Quick Reference

Typical DoD

LiFePO480–90%

Lead Acid40–50%

AGM/Gel50%

Bank Voltage

Small systems12V

Medium systems24V

Larger systems48V

Must Check

Inverter surgeyes

BMS currentyes

Charge currentyes

📚 Engineering Notes

Daily load drives battery sizeBattery bank sizing starts from daily Wh or kWh consumption, not just inverter watt rating.

Battery voltage affects AhFor the same kWh storage, a 48V battery bank needs fewer Ah than a 12V battery bank.

Battery chemistry mattersLead-acid systems usually need more installed capacity because only part of the battery should be used regularly.

Complete the solar workflowPair this with the Solar Panel Output Calculator, MPPT Charge Controller Calculator, Solar Panel Series/Parallel Calculator and Solar String Sizing Calculator.

What is a Solar Battery Bank Calculator?

A solar battery bank calculator estimates the required battery storage capacity for off-grid solar systems, hybrid systems and backup power systems. It converts daily load and backup days into Wh, kWh and Ah capacity.

Solar battery sizing workflow

Start by estimating daily generation with the Solar Panel Output Calculator. Build the PV array with the Solar Panel Series/Parallel Calculator. Check safe string voltage with the Solar String Sizing Calculator, and choose the controller with the MPPT Charge Controller Calculator.

Why autonomy days matter

Autonomy days represent how long the battery should support the load without enough solar charging. More autonomy requires a larger battery bank, especially for cloudy weather or backup power applications.

Why depth of discharge matters

Depth of discharge controls how much of the installed battery capacity is usable. A lower DoD setting increases battery size but can improve battery life, especially for lead-acid batteries.

❓ Frequently Asked Questions

Enter your daily kWh load, backup days and system voltage. The calculator converts the required energy into battery Ah.

Yes. Lithium batteries usually allow deeper discharge, so they often need less installed capacity than lead-acid for the same usable energy.

Battery energy size should be based on daily kWh and backup time. Inverter wattage is important for peak load and surge current checks.