Enter the total power consumption per day, the number of backup days required, maximum depth of discharge, and voltage into the calculator to determine the solar battery bank size.

Solar Battery Bank Size Formula

The following formula can be used to calculate the size of a battery pack for a solar installation.

BB = P * D * DI/100 / V
  • Where BB is the battery bank size (amp hours)
  • P is the power consumption per day (Wh)
  • D is the number of days backup required
  • DI is the maximum depth of discharge (%)
  • V is the voltage (V)

To calculate the solar battery bank size, multiply the power consumption per day by the number of days and again by the maximum depth of discharge, then divide by the voltage.

Solar Battery Bank Definition

A solar battery bank is defined as the total size of a battery required to store a certain amount of energy generated from solar.

Solar Battery Bank Example

The following is an example problem on how to calculate the battery bank size.

  1. First, determine the power consumption per day in watt-hours. For this example, we will say 5,000 watt-hours.
  2. Next, determine the required backup days. Let’s assume 2 days of backup.
  3. Next, determine the maximum depth of discharge and voltage. For this, we will say 90% and 250 volts.
  4. Finally, calculate the battery bank size using the formula and we get 36 amp-hours.


How large of a battery pack do I need?

How large your battery pack needs to be for your solar installation is dependent on two main factors. Your power consumption per day and your needed days of power. The other factors are much smaller when determining battery size. In general, most shoot for 2-3 days of power backup.