Battery Bank Sizing Calculator

About the Battery Bank Sizing Calculator

Sizes a battery bank (in amp-hours) for a target daily energy use, accounting for system voltage, days of autonomy and allowable depth of discharge.

How to use this calculator

1. Enter your daily energy need in watt-hours, \(Wh\).
2. Enter the system voltage in volts, \(V\).
3. Enter the battery depth of discharge as a decimal, \(DoD\), such as \(0.5\) for \(50\\%\).
4. Read the required battery capacity in amp-hours, \(Ah\).

The formula explained

The formula computes the battery bank capacity needed in \(Ah\) from a daily energy requirement. It converts \(Wh\) to \(Ah\) using voltage, then adjusts for how much of the battery you plan to use with \(DoD\).

• Wh = daily energy need in watt-hours
• V = system voltage in volts
• DoD = depth of discharge, written as a decimal
• Ah = required battery capacity in amp-hours

Step by step method

1. Start with the daily energy need in \(Wh\).
2. Divide by the system voltage \(V\) to convert energy to amp-hours.
3. Divide by \(DoD\) to account for only using part of the battery capacity.
4. The result is the battery bank size in \(Ah\).

Worked example

Problem. You need \(2{,}400\\,Wh\) per day, your system voltage is \(24\\,V\), and your depth of discharge is \(0.5\). Find the battery bank size in \(Ah\).

1. Use the formula \(Ah = \\frac{Wh / V}{DoD}\).
2. Substitute the values: \(Ah = \\frac{2{,}400 / 24}{0.5}\). First, \(2{,}400 / 24 = 100\).
3. Then \(100 / 0.5 = 200\), so the required battery bank size is \(200\\,Ah\).

Tips and common mistakes

• Make sure \(DoD\) is entered as a decimal, not a percent, so \(50\\%\) should be \(0.5\).
• If your system has inverter losses or extra loads, the real battery size may need to be larger than the basic calculation.

Frequently asked questions