RV Solar Sizing: Panels, Hours, and What You Actually Recover
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Most people shop for RV solar by panel count. Two hundred watts or four hundred? One folding panel or two on the roof? That is the wrong question until you know how many watt-hours you are trying to put back each day, because a panel’s rating is a laboratory number and the thing you live on is what reaches the battery.
This article is about the recovery side only: what solar actually gives back. Working out the consumption side — the daily watt-hour target you are trying to cover — is the job of our RV power guide. If you have not done that step, do it first; everything below takes that number as its input.
The solar math nobody runs before buying
There is one formula, and everything else in this article is a correction term inside it:
rated watts × peak sun hours × system efficiency = watt-hours recovered per day
Three terms, each of which people get wrong in a predictable way.
Rated watts is the number printed on the panel. It is measured under standard test conditions — bright, cool, perpendicular light — which is not a campsite.
Peak sun hours is not the number of hours the sun is up. It is the number of hours’ worth of full-strength sunlight the panel receives, and it is usually less than half of daylight. The next section defines it properly.
System efficiency is everything lost between the panel face and the battery: angle, heat, dirt, cable, and the charge controller. The section after that takes it apart.
The mistake this formula corrects is multiplying rated watts by daylight hours. A 200 W panel in fourteen hours of summer daylight is not 2,800 Wh. Run the same panel through the real terms and you land closer to 900 Wh — the overstatement is routinely two to three times, which is exactly the size of error that strands people on day three of a trip.
How many peak sun hours you actually get
A peak sun hour is one hour of sunlight at an irradiance of 1,000 watts per square meter, the intensity panels are rated at. A day is described by how many of those hours it adds up to. Morning and late-afternoon sun still counts — it just counts as a fraction.
The range below is the general ballpark used in solar sizing, not a guarantee for any particular place or date:
| Season and conditions | Peak sun hours (ballpark) | What moves it |
|---|---|---|
| Winter, frequent cloud | 2–3 | Low sun angle; roof and tree shade hurt most here |
| Spring and fall, mostly clear | 4–5 | Responds well to tilting a portable panel |
| Summer, mostly clear | 5–6 | Heat derating works against you at the same time |
Four things move your own number: latitude, season, cloud cover, and the parking spot. The first two you plan around; the last one you choose every afternoon. A site under cottonwoods is pleasant to sit in and can cut recovery by more than half, and partial shade on a panel costs more than its shaded fraction, because the shaded cells drag the rest down with them. If you want a real figure for a real place, NREL’s PVWatts calculator gives monthly numbers for a specific location, free.
The practical version: pick the season you will actually be camping in and size for that, not for the annual average. Sizing on a July number and then boondocking in November is how a system that “worked fine last summer” suddenly does not.
Why a 200 W panel doesn’t return 200 watt-hours an hour
The gap between the rating and the battery is a stack of small losses, and they multiply rather than add.
Angle. A panel produces most when the sun hits it square on. A flat roof panel is square to the sun for a moment around solar noon in summer and never in winter. This is the largest recoverable loss, and the only one you can fix for free by tilting a portable panel.
Heat. Panels lose output as the cells warm, and the cells are hottest exactly when the sun is strongest. Manufacturers publish this as a temperature coefficient of power, typically a fraction of a percent lost per degree Celsius above the 25 °C test condition. A panel on a hot roof sits well above air temperature, which is why peak summer sun is not peak summer output.
Dirt and shade. Dust, pollen, and bug splatter take a few percent. A branch shadow across one corner takes far more than a few percent, for the reason above.
The charge controller. A PWM controller pulls the panel down to battery voltage and throws away the difference. An MPPT controller converts it instead, which is why every modern power station uses one — EcoFlow lists 99% MPPT efficiency on the DELTA 2 Max, for example. This is the one term in the stack that is nearly free of loss, provided you do not buy a PWM controller.
Stack it all up and a realistic system efficiency is roughly 65–80% of the theoretical rated-watts × sun-hours figure. Use the low end for a fixed roof panel in shoulder season, the high end for a clean portable panel you actively aim. That range is the same thing said differently as the rule of thumb in our power guide: a flat 100 W panel returns something like 300–500 Wh on a good summer day, three to five times its rating rather than the ten or twelve that daylight hours would suggest.
Portable versus roof-mounted: what changes the math
The two mounting choices change the same term — angle — in opposite directions.
Roof-mounted panels are fixed and flat. They lose real recovery to a bad angle every day of the year and cannot be moved out of shade, but they charge whenever the rig is parked in the open without you doing anything. There is no setup, no cable across the campsite, and nothing to steal. For a weekend camper who is mostly on hookups and wants the battery topped up while driving, that is the right trade.
Portable folding panels can be aimed. Tilting toward the sun and repositioning once or twice a day gets you meaningfully closer to the theoretical peak sun hour number, and — more useful in practice — lets you park the rig in the shade while the panel sits in the sun. The costs are real: setup twice a day, cables to trip over, a panel that cannot be left out while you drive into town, and a security consideration in a busy campground.
Current portable panels are built to fold onto a kickstand for exactly this reason. The EcoFlow 220 W bifacial panel, for instance, is listed at 15.4 lb with a 30–60° adjustable stand and an integrated angle guide — the spec sheet treats aiming as the point of the product, not an accessory.
Full-time boondockers generally end up with both: fixed panels that work unattended, plus a portable one for the days when the only level site is under a tree.
Sizing to your target: how many panels you actually need
Take the daily watt-hour target from the power guide and run it backward through the formula.
The table below is worked for 100 W panels under three named sets of assumptions:
- Conservative: 3 peak sun hours × 70% efficiency = 210 Wh per panel per day
- Average: 4.5 peak sun hours × 75% efficiency = 338 Wh per panel per day
- Good: 6 peak sun hours × 80% efficiency = 480 Wh per panel per day
| Daily target | Conservative | Average | Good conditions |
|---|---|---|---|
| 500 Wh | 3 panels | 2 panels | 2 panels |
| 1,000 Wh | 5 panels | 3 panels | 3 panels |
| 1,500 Wh | 8 panels | 5 panels | 4 panels |
Counts are rounded up, because you cannot buy 4.8 panels. Read the wattage rather than the count if you are shopping larger panels: five 100 W panels and two 220 W panels are close to the same array, and the two-panel version is far less cable and setup.
These are arithmetic examples of the formula, not measurements. Change any assumption — a shadier campsite, a winter trip, a panel lying flat on a roof — and the count moves with it.
Which column to size to is a judgment about how much the trip depends on solar. If solar is your primary recharge and there is no shore power in the plan, size to the conservative column and accept the extra panel. If solar supplements shore power or a generator, the average column is enough; our generator versus battery comparison works through what that backup costs over ten years.
Reading a spec sheet without getting misled
Four numbers matter on a panel’s page, and the headline wattage is only one of them.
Rated watts under standard test conditions. This is the comparable number. Treat any larger “peak” figure with the skepticism you would give a fuel economy claim.
Cell efficiency. It tells you how much power comes out of the panel’s area, which matters when the area is a roof or a storage bay. It does not mean the panel produces more than its rating. Jackery lists 24.3% for its SolarSaga 200 W and 23% for the SolarSaga 100 W; EcoFlow lists 25% for the 220 W bifacial above. Those are close enough that size, weight, and stand design will decide the purchase, not the efficiency line.
Temperature coefficient. Rarely on the marketing page, usually in the full spec table. It is how you compare two panels for a hot climate.
Open-circuit voltage and maximum watts, against your power station’s solar input limit. This is the check most buyers skip and the one that wastes money. Every station lists a maximum solar input in volts, amps, and watts — the DELTA 2 Max accepts up to 1,000 W — and anything beyond that limit is capacity you paid for and cannot use. Voltage matters more than watts here: exceeding the input voltage limit is not merely wasteful, it is a way to damage the controller. The SolarSaga 100 W is listed at 21.6 V open-circuit and 6 A short-circuit, the EcoFlow 220 W at 21.5 V and 12.4 A, which is why panels wired in series need the arithmetic done before you connect them.
Staying inside one ecosystem sidesteps this check: Jackery and BLUETTI both design their panels around their own stations’ input specs, and the pairing is stated on the product page — BLUETTI’s 200 W panel page lists every station it is built to charge. Mixing brands is perfectly fine — it just makes the voltage check your job instead of theirs. For the station side of the decision, capacity and cycle life are compared in our generator versus battery piece.
Panel specifications and prices here were read from the manufacturers’ U.S. and U.K. product pages on September 21, 2026; the BLUETTI details on September 28, 2026. All three makers run frequent promotions, so treat any price as a starting point rather than a quote.
The short version
Solar sizing is not “how many panels fit on the roof.” It is rated watts × peak sun hours × system efficiency, run backward from a watt-hour target you worked out first.
End to end, for a 1,000 Wh day in average conditions: 100 W of panel, 4.5 peak sun hours, 75% system efficiency, 338 Wh recovered per panel, three panels. Winter or shade turns the same target into five. That is the whole calculation, and it takes longer to read than to run.
Once you have your own panel count, the shopping is comparatively easy — pick panels that match your station’s solar input, favor a tilting stand over a slightly higher efficiency rating, and check the temperature coefficient if you camp somewhere hot. Both Jackery and BLUETTI publish the input limits and panel specs you need for that check on the same page as the price — BLUETTI’s Elite 200 V2, for example, states its solar input as 1,000 W max, 12–60 V, 20 A.
