kWh
%
V
Output
Output will appear here
Click in the output to select all text
Solar Battery Calculator
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This Solar Battery Calculator sizes a battery bank for solar backup power, based on your daily energy usage, how many days of autonomy (backup without sun) you want, and the battery's usable depth of discharge — since most battery chemistries shouldn't be fully drained on every cycle to maximize lifespan. Enter your daily usage, desired backup days, depth of discharge percentage, and system voltage, and get the required capacity in both kWh and amp-hours. It's a starting point for sizing off-grid or backup battery storage. Everything runs locally in your browser. Scroll down to enter your numbers.
Features
- Calculates required battery capacity in kWh and Ah
- Accounts for depth of discharge to protect battery lifespan
- Configurable days of backup autonomy
- Instant recalculation as you adjust inputs
Why use this solar battery calculator?
- Avoids undersizing a backup battery system
- No manual kWh-to-Ah conversion required
- Fully private — nothing uploaded
- Free with unlimited use
Frequently asked questions
What is depth of discharge (DoD)?
It's the percentage of a battery's total capacity that's safe to use regularly without significantly shortening its lifespan — lithium batteries often support 80-90% DoD, while lead-acid batteries are typically limited to 50%.
How many days of autonomy should I plan for?
1 day is common for grid-tied backup systems; off-grid systems in areas with extended cloudy periods often plan for 2-3 days or more.
Why does battery voltage matter for the Ah result?
Amp-hours (Ah) and kWh are related by voltage (kWh = Ah × V / 1000), so a higher-voltage battery bank needs fewer amp-hours for the same energy capacity.
Does this account for battery efficiency losses?
No, this calculates the theoretical capacity needed; real battery round-trip efficiency (typically 90-95% for lithium) would modestly increase the practical capacity needed.
Is this specific to lithium or lead-acid batteries?
The formula is chemistry-agnostic — just enter the depth of discharge appropriate for your specific battery type.