Van life · solar
Van solar panel size calculator.
Turn your daily watt-hours into the array watts and panel count needed to refill the battery on a day with your chosen sun hours.
Inputs
Solar array needed
Enter your numbers.
How to size solar panels for a van
Array watts = daily Wh / (peak sun hours x (1 - losses)). Peak sun hours are the full-sun-equivalent hours your location gets in a day; the U.S. Department of Energy notes that solar radiation data for PV are usually given in kilowatt-hours per square metre, which is where sun-hour figures come from. Look up your own location and season in a tool such as NREL PVWatts.
Worked example. 875 Wh a day, 4 peak sun hours and 25% losses: 875 / (4 x 0.75) = 292 W. With 100 W panels that is 3 panels, 300 W installed. Dividing 300 W by 12 V gives a rough 25 A at nominal voltage; the controller must be rated for its manual's current and voltage limits, so check those instead of this number.
Limits. The 25% loss figure and the 4 sun hours are placeholders, not published standards. Roof space, shade, tilt and winter sun can all cut real output. A roof that fits fewer panels means you reduce the load or add another charging source.
Frequently asked questions
How many solar panels do I need for a camper van?
Divide daily watt-hours by peak sun hours and by one minus your losses. For 875 Wh a day, 4 sun hours and 25% losses that is about 292 W, or 3 panels of 100 W.
What are peak sun hours?
Peak sun hours are the full-sun-equivalent hours of sunlight your location gets in a day. Look up your location and season in a tool such as NREL PVWatts; do not assume the summer value in winter.
How many watts of solar do I need to run a 12V fridge?
A fridge that uses 360 Wh a day needs 360 / (4 x 0.75) = 120 W of panel at 4 sun hours and 25% losses. Your fridge, climate and sun will differ.
Does this size the charge controller?
Only roughly. The current shown is array watts divided by nominal battery voltage. Choose a controller from the manufacturer's current and input-voltage limits.
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Planning estimate, not professional advice
Results are planning estimates from the numbers you enter. They are not professional, engineering, electrical or safety advice and are not a substitute for the manufacturer's instructions or local code. Battery banks, inverters and DC wiring can start fires or injure you if built wrongly: size cable and fuses to the equipment manual, fuse every positive conductor close to the battery, and have a qualified electrician check the build.