How to size RV or boat solar
Convert your daily use to watt-hours, then divide by peak sun hours and a realistic efficiency factor. Panels on boats and RVs are usually mounted flat, get hot and are partly shaded, so plan for 70–80% of their rating.
Daily Wh = Daily Ah × Battery volts
Solar watts = Daily Wh ÷ (Sun hours × Efficiency)
Example
100 Ah per day at 12 V is 1,200 Wh. With 5 sun hours and 75% efficiency: 1,200 ÷ 3.75 = 320 W, so two 200 W panels (400 W) with a 40 A MPPT controller.
Quick guide
| Setup | Daily use | Solar |
|---|---|---|
| Weekend camper: lights, phone, fan | 30–50 Ah | 100–200 W |
| Van life with 12 V fridge | 60–100 Ah | 200–400 W |
| Full-time RV, laptop work | 150–250 Ah | 600–1,000 W |
| Cruising sailboat | 100–200 Ah | 400–800 W |
Frequently asked questions
How much solar do I need to run an RV fridge?
A 12 V compressor fridge uses 30–50 Ah per day, which about 150–200 W of solar can replace in good sun.
Can RV solar run the air conditioner?
Rarely. A rooftop A/C uses 1,300+ W while running, which needs a large lithium bank and well over 1,000 W of panels.
Should I tilt my RV panels?
Tilting toward the sun can add 20–40% in winter, but most RVers mount flat for simplicity and add more wattage instead.