Solar Battery Bank Calculator: How to Size It Right - OneSDR

Planning a solar power system? One of the most important parts is your battery bank — it stores energy for nighttime use and cloudy days. But how big does your solar battery bank need to be?

Let’s break it down with simple steps and an online calculator to make it all click.

Table of Contents

🔋 What Is a Solar Battery Bank?

A battery bank is a group of batteries that store the energy collected from your solar panels. It’s your backup power source when the sun isn’t shining — like at night or during cloudy weather.

Proper sizing ensures you:

Have enough backup power
Don’t overspend on unnecessary batteries
Protect your appliances and electronics

📐 How to Calculate Battery Bank Size

To size your solar battery bank, you need to know:

Daily energy usage (Wh) – how much power your devices use per day
Days of autonomy – how many days you want backup power
System voltage (V) – typical choices are 12V, 24V, or 48V
Depth of discharge (DoD) – percentage of usable battery capacity (e.g. 80% for lithium)

🔢 Battery Bank Size Formula

Battery Bank (Ah) = (Daily Energy × Days of Autonomy) ÷ (Voltage × DoD)

Where:

Daily Energy is in watt-hours (Wh)
Voltage is your system voltage (V)
DoD is expressed as a decimal (80% = 0.8)

📉 What is Depth of Discharge?

⚙️ Example

Let’s say:

Daily energy use = 5,000 Wh
Days of autonomy = 2
System voltage = 24V
DoD = 80% (0.8)

Battery Bank = (5,000 × 2) ÷ (24 × 0.8)
             = 10,000 ÷ 19.2
             = 520.83 Ah

So you’d need a battery bank of at least 520.83 amp-hours at 24V.