Solar Battery Calculator

Solar Battery - figures update as you type, nothing leaves your browser.

Maintained by Roshan.

Use Solar Battery Calculator

Figures update as you type. Nothing you enter leaves this tab, and no values are stored.

Daily energy to store (kWh)Days of autonomy (days)Battery voltage (V)Usable depth of discharge (%)

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About Solar Battery Calculator

A solar battery calculator sizes the battery bank you need to store a given amount of energy, in amp-hours, from your daily usage, how many days of backup you want, the battery voltage, and how deeply the batteries can safely discharge. Undersize the bank and you run flat overnight or in a cloudy spell; oversize it and you pay for capacity you never use. This gives you the figure to design or check a system against. The tool converts your daily energy into watt-hours, multiplies by the days of autonomy you want, then divides by the battery voltage and the usable depth of discharge to get amp-hours. Depth of discharge matters a lot: lithium banks tolerate 80–90%, lead-acid closer to 50%, and discharging deeper shortens their life. The result is the usable capacity to aim for; add a margin for cold weather and ageing, and remember charging and inverter losses sit on top.

Using Solar Battery Calculator

Enter daily energy demand in kWh and the number of days you want without charging.
Set battery voltage and usable depth of discharge for the chemistry you plan to use.
Read the estimated amp-hour capacity, then account separately for inverter losses and ageing.

Where solar battery calculator helps

Sizing an off-grid bank

Storing 10 kWh for one day at 48 V and 80% usable needs about 261 Ah of battery.

Keep bank energy separate from charging capacity

For 10 kWh of usable storage with an 80% usable fraction, the nominal energy requirement is 12.5 kWh. At 48 V that is about 260.4 Ah before any extra system losses or reserve. This sizes an energy store from your assumptions; it does not size solar panels or guarantee recharge during a cloudy day. Use the battery manufacturer's permitted operating range when choosing the usable fraction.

Before you use the result

The result does not include inverter losses, temperature effects or battery ageing. Check the manufacturer's usable-capacity limits before sizing a system.
It calculates in your browser from the numbers you enter, so a wrong input gives a wrong result - sanity-check the figures.
Nothing is saved between visits; note down or screenshot the result if you need to keep it.

Questions about Solar Battery Calculator

What depth of discharge should I use?

About 80–90% for lithium, 50% for lead-acid - going deeper shortens battery life. Enter the usable figure and the tool sizes the bank accordingly.

Is my data saved or uploaded?

No. Solar Battery Calculator calculates the result entirely in this browser; the values you enter are not stored or sent to a server.