Battery Capacity Calculator

Enter the load power and the backup duration and, if needed, change the assumptions. All default parameters are marked as unconfirmed.

This is an indicative estimate, not a power supply design. Elevators, pumps and motors need an engineering calculation. Installation and connection must be done by qualified specialists only. The platform does not accept funds.

Sum of the rated power of the appliances that must keep running during an outage. Allowed range: from 1 to 1,000,000 W.

From 0.5 to 24 hours. Allowed range: from 0.5 to 24 h.

The share of power actually used on average. If you are not sure, leave 100. Allowed range: from 1 to 100 %.

Depends on the battery chemistry and the BMS; from 50 to 95. Allowed range: from 50 to 95 %.

From the inverter datasheet; from 80 to 99. Allowed range: from 80 to 99 %.

From 0 to 100. Allowed range: from 0 to 100 %.

From 0 to 40. Allowed range: from 0 to 40 %.

Your result

Fill in the form and press 'Calculate'.

Calculation example

Fictional input data for illustration. This is not a real building and not a recommendation.

Input data: Total power of critical loads: 1500 W; Required backup duration: 8 h; Simultaneity factor: 100 %; Allowed depth of discharge (DoD): 80 %; Inverter efficiency: 92 %; Reserve: 20 %; Capacity loss due to temperature: 10 %.

Estimate range
IndicatorLowTargetHigh
Nominal battery capacity, kWh20,1327,1736,68
Usable energy, kWh11,5915,6521,13
An engineering calculation is required: the result is incomplete or depends on unconfirmed data.

The result is indicative and is not a power supply design or a promise of backup duration.

Missing data:

  • Power factor (cos φ): Aggregate load
  • Insufficient data: an engineering calculation is required.

Calculation module version: 1.0.0.

How it is calculated

  • Energy = power × hours × duty factor.
  • Usable energy = energy × (1 + reserve) / efficiency.
  • Nominal capacity = usable energy / DoD / (1 − temperature) / (1 − ageing).

Assumptions (unconfirmed, replace with equipment data)

  • An ageing reserve of 20% is used by default and is an unconfirmed assumption.
  • DoD, efficiency and temperature loss values should be taken from the documentation of the specific equipment.

Limitations

  • Battery voltage, charge and discharge currents, the number of modules and compatibility with the inverter are not calculated.
  • The result is not a promise of backup duration.

Frequently asked questions

How does usable capacity differ from nominal capacity?

Usable capacity accounts for inverter losses and the reserve; nominal capacity also accounts for depth of discharge, temperature and ageing.

Can the default values be trusted?

They are unconfirmed assumptions for a first estimate. Replace them with the manufacturer data.

Start an initiativeView SunEco equipmentPartner commercial offerSunEco catalogue: a link to a specific product is not confirmed, the supplier's home page will open. SunEco is a separate supplier; you are free to choose any other.

Would you like to be contacted? (optional)

Leave your contact only if you agree. Data is not passed to SunEco or other suppliers automatically.