Solar Battery Backup Calculator
List the appliances you run on solar, pick your battery system voltage and battery type, and get your daily energy use, the required battery capacity in amp-hours, and a suggested battery setup.
Your Appliances
| Appliance | Watts | Qty | Hours / Day |
|---|
Your Result
How to use
- Add each appliance with its watts, quantity and how many hours per day it runs.
- Select your battery system voltage (12V, 24V or 48V) and battery type.
- Set days of autonomy if you want backup for cloudy days without charging.
- Click Calculate Battery Size to see daily watt-hours, required amp-hours and a suggested battery configuration.
Frequently Asked Questions (FAQ)
What does this calculator tell me?
It tells you your total daily energy use in watt-hours, the battery capacity in amp-hours you need at your chosen system voltage, and a suggested battery setup such as 4 x 200Ah 12V batteries: 2 series x 2 parallel for a 24V system.
What is the difference between lead-acid and lithium settings?
Lead-acid batteries should only be discharged to about 50 percent of their capacity, while lithium batteries can safely discharge to about 90 percent. The calculator uses these depth-of-discharge values by default, and you can adjust the percentage yourself.
What are days of autonomy?
Days of autonomy is how many days the battery bank should power your home without any solar charging, for example during cloudy days. More days mean a bigger battery bank.
How is the battery setup suggestion made?
The tool uses standard 200Ah 12V batteries as the building block. It calculates how many batteries are needed in series to reach your system voltage and how many parallel strings are needed for the required amp-hours, then shows the result as series x parallel.
Is this calculator free to use?
Yes. It is free with no signup.