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Solar battery size calculator

Estimate the battery capacity you need from daily energy use and days of autonomy.

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Need Battery capacity (kWh)? The Solar battery size calculator derives it from Daily energy use (kWh), Days of autonomy, Usable depth of discharge (%) in one step. For instance, with Daily energy use (kWh) = 10, Days of autonomy = 2 and Usable depth of discharge (%) = 80 it returns Battery capacity (kWh) = 25.

How to use it

  1. Enter your values: Daily energy use (kWh), Days of autonomy, Usable depth of discharge (%).
  2. Read the result instantly: Battery capacity (kWh).

Frequently asked questions

How does the Solar battery size calculator work?

It takes Daily energy use (kWh), Days of autonomy and Usable depth of discharge (%) and derives Battery capacity (kWh) from them. The calculation is live as you type, so the result updates on every change.

Which values does the calculator ask for?

3 values: Daily energy use (kWh), Days of autonomy and Usable depth of discharge (%). Nothing else is required — no account, no file upload.

What does a typical calculation look like?

With Daily energy use (kWh) = 10, Days of autonomy = 2 and Usable depth of discharge (%) = 80, the calculator returns Battery capacity (kWh) = 25. Those figures come from running this exact tool, so you can reproduce them by entering the same values.

How much does the result change with different inputs?

It moves a lot. Using Daily energy use (kWh) = 20, Days of autonomy = 4 and Usable depth of discharge (%) = 160 instead, Battery capacity (kWh) goes from 25 to 50 — which is why it is worth testing a few scenarios rather than trusting a single figure.

What does it give for smaller values?

Scaled down to Daily energy use (kWh) = 5, Days of autonomy = 1 and Usable depth of discharge (%) = 40, Battery capacity (kWh) comes out at 12.5. The relationship is worth checking at both ends before you rely on a single result.

When would I actually use this?

Putting a number on a bill: what an appliance costs to run, whether a solar array covers the load, and how much heating a room actually needs.

What is the most common mistake?

Confusing power with energy. A kilowatt is a rate and a kilowatt-hour is a quantity; a 2 kW heater on for half an hour uses 1 kWh, and only the second figure appears on a bill.

What is the difference between the Solar battery size calculator and the Solar panel calculator?

This one returns Battery capacity (kWh); the Solar panel calculator returns Panels needed and System size (kWp). That is the whole difference — open the one whose figure you need.

Is there a tool for the next step?

Battery life calculator is the closest one after this: Estimate how long a battery lasts from its capacity and the load current.

What else is worth having open alongside it?

Water Heater Size Calculator and Generator size calculator — they come up in the same task often enough to be worth a second tab.

Further reading

All guides →
How-toWhat Size Solar Battery Do I Need? Sizing by Daily UseSize a solar battery from your daily energy use, the days of autonomy you want, and the battery's usable depth of discharge.How-toHow Many Solar Panels Do I Need? A Simple Sizing MethodSize a solar array from your annual electricity use, panel wattage, and local sun hours — plus a quick payback estimate in dollars.How-toHow to Convert kWh to CO₂: Grid Emission Factors ExplainedConvert electricity in kWh into CO₂ emissions using your grid's emission factor — and understand why that factor differs so much by country and time.ComparisonSolar Panels: the Self-Consumption Rate Decides the PaybackSince June 2026 a French rooftop is paid 1.1 cents for an exported kilowatt-hour and avoids 25.61 cents by consuming the same one. That ratio of 23 to 1 makes the self-consumption rate — the variable almost every quote omits — worth more than the amount of sun falling on the roof.How-toWhat Size Water Heater Do I Need?Match tank size to household size and peak-hour demand: roughly 40–50 gallons for two people, more as bathrooms and simultaneous use grow.How-toWhat Size Generator Do I Need? Add Up Your Running and Starting WattsSize a generator by listing the appliances you must run, adding their running watts, and allowing headroom for the surge when motors start.