The question people ask is how many watts of panel. The question that decides the system is how many amp-hours a day you use, because that number sizes the battery and the panels both.
Work it out before shopping. A day's consumption in an RV is a short list.
The daily budget
Twelve-volt loads, typical amp-hours per day:
| Load | Ah/day |
|---|---|
| 12 V compressor fridge | 40–60 |
| LED lighting | 5–10 |
| Water pump | 3–5 |
| Roof vent fan | 10–25 |
| Phone and laptop charging | 10–20 |
| Furnace fan (cold nights) | 15–30 |
| Inverter standby | 5–15 |
Two things stand out. The fridge is most of the budget — often more than everything else combined, and it runs whether you are awake or not. And inverter standby is a real line item: an inverter left switched on draws current continuously to power nothing.
A modest setup lands around 60–80 Ah/day. With a fridge, fans and laptops, 100–150 Ah/day is normal.
Battery first
The battery carries the night and the cloudy days; panels only refill it.
Rules of thumb, using LiFePO4 at 80–90% usable:
- Weekend use, 60 Ah/day — 100 Ah battery. One night comfortably.
- Extended use, 100 Ah/day — 200 Ah. A night plus margin.
- Full-time, 150 Ah/day — 300–400 Ah, so a dull day does not end the trip.
With lead-acid, double those figures for the same usable capacity — see LiFePO4 or lead-acid. In a vehicle the weight difference alone usually settles it.
Then the panels
Panels must replace the day's consumption in the hours actually available. A useful planning figure for flat-mounted RV panels is roughly 3.5 to 4.5 peak sun hours in summer, considerably less in winter or under trees.
watts needed ≈ (Ah/day × 12 V) ÷ peak sun hours ÷ 0.75
The 0.75 covers charge controller losses, heat and imperfect conditions.
At 100 Ah/day and 4 peak sun hours: (100 × 12) ÷ 4 ÷ 0.75 = 400 W.
Which matches what people arrive at by experience:
- 200 W — weekend camping, no fridge or a small one.
- 400 W — the common full-time starting point.
- 600–800 W — full-time with air conditioning ambitions, or northern latitudes.
Roof space is the real limit
Rigid panels need roughly 17 to 21 square feet per 100 W. Four hundred watts is around 70–85 square feet of clear roof — before vents, the air conditioner, the antenna and the skylight.
Measure the actual clear rectangles on your roof before choosing a wattage. On many rigs the roof, not the budget, sets the ceiling.
Flat mounting costs you output
RV panels lie flat because tilting them on a moving vehicle is impractical. That flat orientation gives up something like 10–25% against an optimally tilted array, and the loss is worst in winter when the sun is low and you need it most.
Tiltable mounts recover much of it but must be lowered before driving, every time. Most full-timers conclude the extra panel is easier than the ritual. See tilt angle for the size of the effect.
Two more things worth knowing before buying:
- Shade is not proportional. One branch across one panel can cost far more than its share — the reason is in shading loss.
- MPPT, not PWM. On a 12 V system with higher-voltage panels the difference is real money, covered in MPPT or PWM.
FAQ
How many solar panels do I need for an RV?
Work from amp-hours per day. Weekend use is typically 200 W, full-time around 400 W, and 600–800 W if you want air conditioning or camp in northern latitudes.
Will 400 W of solar run an RV air conditioner?
Not on its own. Rooftop air conditioners draw far more than 400 W of panel can supply, and running one on battery needs a large bank plus a high-output inverter.
How much roof space does 400 W need?
About 70 to 85 square feet of clear space for rigid panels, before vents and the air conditioner are subtracted.
Should RV panels be tilted?
Tilting gains 10–25%, most of it in winter, but the panels must be lowered before every drive. Most full-timers add a panel instead.
How big a battery do I need with 400 W of solar?
Match it to your daily consumption, not to the panels — around 200 Ah of lithium for 100 Ah a day of use.