Maker Label Studio Environmental, EHS & Energy

Solar Battery Bank Sizing Calculator

Estimate off-grid battery bank capacity from daily energy load, autonomy, depth of discharge, system voltage, efficiency, and selected battery size.

Inputs

Use a total daily load or build one from an appliance table.

Watt-hours per day. Example: 5000 Wh/day for a small off-grid cabin.
Appliance Watts Qty Hours/day Daily Wh Remove
1,200 Wh
400 Wh
720 Wh
Appliance load: 2,320 Wh/day
Days the bank should run without charging.
Use a decimal from 0.01 to 1.00.
Use inverter, wiring, and battery efficiency as a decimal.
Ah per battery at the selected system voltage.

Results

Battery capacity is calculated from the off-grid sizing formula in the specification.

Required capacity
-Ah
Required energy
-kWh
Batteries required
-batteries
Load basis -
Battery assumption -
Inverter sizing note

-

Cited category Environmental, EHS & Energy. Verify current codes, standards, manufacturer data, and authority requirements before design or installation.
Formula used: Ah = (daily Wh x days of autonomy) / (depth of discharge x system voltage x efficiency) and kWh = daily Wh x autonomy / DoD / 1000.

Self-tests

Golden tests check the core Ah formula and battery count rounding.

Self-tests have not been run.

About the Solar Battery Bank Sizing Calculator

Off-grid homeowners, solar installers, RV owners, and telecom technicians use a solar battery bank calculator to estimate storage capacity from daily energy use, autonomy days, battery voltage, depth of discharge, and efficiency losses. Enter loads and system assumptions to calculate amp-hours or kilowatt-hours. It helps avoid undersized storage that fails during cloudy periods or high demand.

How it works

  1. List the daily watt-hour use for all critical loads.
  2. Choose the number of autonomy days the battery must cover.
  3. Enter system voltage, usable depth of discharge, and efficiency assumptions.
  4. Calculate required battery capacity in kilowatt-hours and amp-hours.
  5. Compare the result with manufacturer ratings and code-compliant installation limits.

Frequently asked questions

How do I size a solar battery bank?

Start with daily energy use, multiply by autonomy days, then adjust for allowable depth of discharge and system efficiency. Convert watt-hours to amp-hours by dividing by battery bank voltage.

Why does depth of discharge matter?

Depth of discharge defines how much of the rated battery capacity you plan to use. Using less of the battery can improve reserve margin and may extend life, depending on the chemistry and manufacturer limits.

Should I size batteries from average load or peak load?

Use daily energy for capacity, but check peak load separately for inverter power, surge current, and battery discharge current. A battery bank can have enough energy but still fail on startup surge.

Are lithium and lead-acid battery sizes calculated the same way?

The energy math is similar, but usable depth of discharge, efficiency, temperature behavior, charge profile, and cycle life differ. Use chemistry-specific manufacturer data for final sizing.

Does this replace a full solar production model?

No. Battery sizing should be paired with solar array production, seasonal weather, shading, generator backup, and charge-controller limits for a complete off-grid design.

References