Size a solar array for an RV, camper van or off-grid cabin. Don't know your daily use? Use the daily energy use calculator first.
Solar watts = daily Wh ÷ (peak sun hours × efficiency). Peak sun hours are not daylight hours: they are the equivalent hours of full 1,000 W/m² sun, usually 3–6 in the US depending on season and location (lower in winter and the northern states). 75% efficiency is a typical real-world allowance for heat, wiring, controller and flat-mounted RV panels that are not tilted toward the sun.
| Setup | Daily use | Solar |
|---|---|---|
| Weekend camper (lights, fan, phone) | 300–600 Wh | 100–200 W |
| Van with 12V fridge + laptop | 800–1,500 Wh | 300–450 W |
| Full-time RV, residential fridge | 2,500–4,000 Wh | 800–1,200 W |
| Running the roof AC | 8,000+ Wh | Usually impractical on solar alone |
Safety: These are general estimates, not a design. Follow your equipment manufacturer's instructions and local electrical code, and consult a qualified electrician for anything connected to shore power, a house, or high-current batteries.
Divide your daily watt-hours by peak sun hours times about 0.75. A 1,200 Wh/day RV with 4.5 sun hours needs about 355 W, or two 200 W panels.
Rarely on solar alone. A 13,500 BTU AC uses about 1,200–1,500 W while running, so 8 hours needs around 10,000 Wh per day, which takes well over 2,000 W of panels plus a large lithium bank.
The number of hours per day that equal full-strength sunlight (1,000 W per square meter). Most of the US gets about 3–6.
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