Solar Panel Size Calculator

Enter how much energy you use per day and how much sun you get. You'll see the panel wattage you need, a practical panel combination, and how long a full recharge takes.

Daily energy use (Wh)

Your sunlight (pick a rough guide)

Peak sun hours per day

Panel setup (real-world output)

Battery to recharge (Wh, optional)

Panel wattage needed

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rated (STC) watts

Practical setup

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Energy harvested / day

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with the exact wattage above

Full recharge time

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Check your power station's solar input limit. Most portable units cap solar input at a fixed number of watts and a voltage range. Extra panels beyond that limit add no charging speed, and exceeding the voltage limit can damage the unit. Check the "solar input" spec before buying panels.

How the solar sizing math works

A panel's rating, like "200 W", is measured in a lab under standard test conditions: full, direct sunlight of 1,000 watts per square meter at a cell temperature of 25 °C. Outdoors, you rarely get that, so two numbers bring the rating back to reality:

Peak sun hours compress a whole day's changing sunlight into the equivalent number of hours at full lab-strength sun. Four peak sun hours doesn't mean four hours of daylight. It means the day's total sunshine adds up to four "perfect" hours. Our peak sun hours guide explains how to look up your location.
Real-world output covers losses from heat (panels produce less when hot), dust, wiring, the charge controller, and imperfect angle. Around 75% is a sensible planning figure for fixed panels. Portable panels lying flat on the ground often do worse.

Panel watts = Daily Wh ÷ (peak sun hours × real-world output)
Recharge time (sun-hours) = Battery Wh ÷ (panel watts × real-world output)

Worked example

Using 1,700 Wh per day, 4 peak sun hours and fixed panels at 75%: 1,700 ÷ (4 × 0.75) ≈ 567 W of panels. Rounded up to standard sizes, that's six 100 W panels or three 200 W panels. In winter, with around 2 peak sun hours, the same load would need roughly twice the panel wattage. That's why many off-grid setups are sized for the worst month, not the average one.

Frequently asked questions

Should I size for summer or winter?

If you depend on solar year-round, such as in a cabin or a full-time RV, size for your darkest month. For summer camping, the summer figure is fine. For emergency backup, many people size for an average day and accept that a cloudy stretch will mean rationing.

Do I need an MPPT charge controller?

Nearly every modern portable power station has an MPPT controller built in. For a DIY system, an MPPT controller typically harvests noticeably more energy than a cheaper PWM controller, especially in cold weather or when panel voltage is well above battery voltage.

Why does the recharge time assume I'm not using power?

It shows the time to refill an empty battery with nothing else connected. If you're running devices while charging, they use some of the solar output first, so add their daily use to the battery size for a rough answer.