RV solar sizing calculator

Start with energy, not roof space

A panel’s watt rating describes power under specified conditions. Your RV uses energy over a whole day, measured in watt-hours. Begin with that daily energy budget and estimate how much useful sun you can collect.

The result is rounded up to the next 50 watts for an initial planning target. That rounding is a display choice, not a specification for the equipment you must buy.

A 1,000 Wh/day example

With 4 peak sun hours, a 75% delivery factor, and a 20% margin, the calculation is 1,000 × 1.2 ÷ (4 × 0.75) = 400 watts. Under the same assumptions, 400 watts would deliver an estimated 1,200 Wh per day.

Drop the sun input to 2 peak hours and the modeled requirement doubles to 800 watts. This is why a setup that works in an open summer campsite can fall short in winter or under trees. The tool does not fetch weather or site-specific sunlight data.

Peak sun hours are not hours of daylight

Peak sun hours express the equivalent energy of full-strength sunlight over a day. Use an estimate appropriate to your location, season, panel orientation, and site exposure. If you expect heavy shade, a sunny-area regional average can be misleading.

The delivery factor groups losses into one adjustable value. The default 75% is an example allowance, not a measured efficiency. Panel temperature, wiring, the controller, conversion, orientation, and shading affect delivered energy in different ways. Avoid counting the same loss twice if your source already reports energy delivered to the battery.

Solar size does not answer every power question

• Battery capacity: enough usable storage must remain for the night and poor-weather periods.
• Charge controller: voltage, current, and array configuration must match the controller’s ratings.
• Roof and mounting: account for real dimensions, obstructions, attachment requirements, and shade.
• Peak loads: sufficient daily energy does not guarantee an inverter can start or run a large appliance.

Use this as a starting energy estimate, then check your equipment manuals and a qualified installer’s design. It does not size cables, fuses, batteries, inverters, or mounting hardware.

Try a low-sun plan too

Run the calculator for your expected conditions and again for a poor-weather day. Decide whether you will reduce discretionary use, use an appropriate backup charging option, or leave for a powered campsite. More panels cannot guarantee sunshine.

The battery runtime calculator helps you estimate your buffer when charging is limited. Use measured energy at the battery/DC system for its solar input whenever available.