Solar Panel Calculator

Enter daily energy use, peak sun hours and system losses to size the array and the battery bank.

Solar panel calculator

Daily energy use (kWh)

Peak sun hours per day

System losses (%)

Panel rating (W)

System voltage

Days of battery autonomy

Array size needed: —

Panels needed: —

Installed array power: —

Usable battery capacity: —

Battery bank at 50% discharge: —

Battery bank in amp hours: —

—

The array size divides the daily energy plus losses by the peak sun hours, and the battery bank covers the days of autonomy you choose.

Enter your daily energy use in kilowatt hours.
Set the peak sun hours, the system losses and the panel rating.
Choose the system voltage and the days of autonomy, then read the array and battery sizes.

Common questions about the free online solar panel calculator.

Multiply daily energy use in watt hours by one plus the loss fraction, then divide by the peak sun hours for your location.

Peak sun hours express the daily solar energy as hours of full strength sunshine. Most places average between 3 and 6 hours per day.

Divide the array size in watts by the rating of one panel and round up, so a 4400 watt array needs eleven 400 watt panels.

Multiply daily energy use by the days of autonomy, then double it if the battery should not be discharged below fifty percent.

Multiply kilowatt hours by one thousand and divide by the system voltage. A 24 kWh bank at 48 volts is 500 amp hours.

Use about 25 percent to cover inverter losses, wiring, dust, heat and battery charging inefficiency in a typical off grid system.

No. The voltage sets the current and the wiring, while the array size in watts and the number of panels stay the same.

No. The solar sizing is calculated in your browser, so the energy figures you enter never leave your device.

Yes. It is free to use, needs no account, and you can compare as many locations and loads as you like.

Last updated: October 10, 2026