How Many Solar Panels for a Camper

The number on the box is not the number you’ll use. A panel rated 100W doesn’t deliver 100 watt-hours for every hour of sun — field experience puts the real daily harvest closer to a third of nameplate, once weather, angles, and the clock are factored in. Beginners count panels; they should be counting watt-hours. And here’s the harder truth: even getting the panel math right is the second problem. The first problem is storage. Panels only determine how fast you refill a battery the next day — if the battery isn’t big enough to hold a night’s worth of loads, no panel count fixes that.

This guide works backward from what you actually run. Size your daily energy budget first, match battery storage to it, then choose panels that can refill that storage in a reasonable day of sun. That’s the sequence. Everything else is detail.

Why Your Panel’s Rating Is a Ceiling, Not a Promise

A 100W panel produces 100W only under laboratory conditions: perpendicular sun, moderate temperature, no haze, no wiring losses. That moment, even on a clear day, lasts roughly 10am to 4pm — and only if nothing is in the way. People who’ve actually monitored their rigs report output hovering around 85% of rated in bright direct sun, dropping to 20–30% under cloud cover. Multiply that across a full day of variable sky and you get roughly 300–400 Wh harvested per 100W of panel capacity. A conservative working figure used by experienced campers is around 350 Wh per 100W per day.

The classic beginner mistake is multiplying nameplate watts by hours of daylight: “100W × 6 hours = 600 Wh.” Real harvest is closer to half that. The naive math double-counts the sun.

Flat roof mounting makes this worse. A panel rated at any wattage is rated at a perfect perpendicular angle to the sun — an angle a fixed, horizontal rooftop almost never achieves. Field observation puts the flat-mount penalty at roughly 25% compared to a tilted or repositionable panel. A portable panel you can prop and reposition to follow the sun will genuinely out-produce a fixed rooftop panel of the same rating, especially in the shoulder seasons when the sun stays low. The trade is convenience: no setup, no theft risk, no tangled cables — but you pay for that in harvest.

The upshot is that a 200W roof array isn’t twice as good as a 100W array in any simple sense. It’s two panels each operating well below their label, mounted flat, producing somewhere in the neighborhood of 600–800 Wh on a decent day. Plan around that reality, not the spec sheet.

Start With What You Run, Not How Many Panels You Want

Panel count is the output of the calculation, not the input. The input is your daily energy load in watt-hours. Add up everything you run and roughly how long you run it — fridge, lights, fan, phone, laptop, whatever. That total is your Wh/day budget, and it determines everything downstream.

One method that’s seen use among van builders: take your daily Wh, divide by roughly 5 peak sun hours, divide again by 0.8 for system efficiency losses, then add 30–50% buffer for cloudy days and seasonal dips. That’s your panel-wattage target. The math won’t give you a precise answer — there are too many variables — but it will tell you whether you’re in the 200W territory or the 600W territory, which matters enormously.

Usage tiers, tied to Wh/day budgets from one builder-adjacent source (treat these as orientation, not hard specs):

• Weekender / minimalist (~950 Wh/day — lights, phone, small fridge, minimal loads): 200–300W of panel
• Standard use (~1,550 Wh/day — full fridge, laptops, fans, some USB charging): 300–400W
• Power-hungry / full-time (~2,500 Wh/day — HVAC, induction cooking, work setup, large loads): 600–1,000W+

These tiers come from a single source writing in a sales context, so hold them loosely. What they’re really telling you is that “how many panels” is entirely a function of what you run. A bare-bones weekender and a full-time remote worker living in the same van need radically different arrays — not because of the van, but because of the loads. The naked answer of “get 400W” is meaningless without the Wh/day number behind it.

One more variable that drives the calculation more than most people expect: how many sun hours you’re actually planning around. Use 5 peak sun hours per day as a conservative year-round figure; the continental US average is closer to 6, and sunny summer states can hit 5–6 reliably. But winter at higher latitudes is notably less than either — and a system sized to a summer average can fall dramatically short in December. If you camp year-round or at northern latitudes, plan to the lower number. The buffer you build in at the sizing stage is your cheapest insurance.

Battery First, Then Panels

Here’s where most systems go wrong: people over-invest in panels and under-size storage, then wonder why they’re running out of power every night despite a big array. Solar sets the refill rate. The battery is the tank. If the tank is too small, a faster fill doesn’t help you — you needed more tank.

A starting guideline that shows up across multiple sources is roughly 200W of solar per 100Ah of usable battery capacity. Framed the other way: 100Ah of battery per 200W of panel. One full-time boondocker running a large bank pushed that ratio as high as 2.7W per 1Ah — nearly triple the baseline — because they were maximizing roof solar against heavy overnight draws and frequent cloudy stretches. Different goals, different ratios. The range is real, not a contradiction.

The ratio also shifts depending on what’s actually constraining you:

• If you have plenty of battery but run out of sun to refill it, you’re charge-rate limited — more panels help.
• If you have plenty of panels but run dry by 10pm, you’re storage limited — more battery helps.
• If you camp in frequent overcast and need to ride out two or three gray days, you need more of both.

Battery chemistry matters here too. Lithium iron phosphate (LiFePO4) is the consensus choice for camper solar — it lets you use a far greater portion of its rated capacity before damage, so a 100Ah lithium battery delivers roughly the usable energy of a 200Ah AGM. If you’re running AGM or lead-acid, you effectively need to buy twice the rated capacity to get the same usable storage, and you’ll likely need more panel to refill a bigger bank.

There is one cold-weather gotcha that almost nobody mentions: LiFePO4 cells will refuse to accept a charge when the battery temperature is below freezing. The solar can be producing fine, the controller is trying to push current in — and the battery management system shuts the door. If you camp in winter, this isn’t theoretical. An internal battery heater, or a heated storage compartment, is the solution most winter campers eventually land on. It’s the omission that bites people who bought lithium expecting it to just work in January.

How Much Roof Do You Actually Have?

Once you know how many watts you need, the roof may disagree. Physical real estate is a hard ceiling that no amount of calculation overrides.

A Sprinter 144 — one of the most common van platforms — typically fits 300–525W flat-mounted, depending on roof accessories, and can push toward 800W with a rack setup. A full-size motorhome with a large battery bank, maximizing every square foot, topped out around 5,020W in one documented case (a combination of flat panels and liftable sections). That’s the ceiling for a very large rig — and it was the physical limit, not a budget one.

Before you buy panels, sketch your roof. Vents, fans, air conditioning units, antennas, and walkable areas all eat real estate. Non-standard panel dimensions can leave awkward gaps that waste space. People who calculate a wattage target and then assume the roof will accommodate it are regularly surprised. Layout is the constraint that shows up last and costs the most to fix.

What It Costs — and What the Price Tags Usually Leave Out

Cost figures for camper solar come almost entirely from installer-adjacent sources, so treat these as rough orientation, not market data. From one 2026 source:

Professional installation runs roughly 30–50% more than a comparable DIY build, and typically includes warranty coverage and proper system commissioning. The labor premium is real but so is the expertise for roof penetrations and wiring done right the first time.

The more important warning: quoted panel-kit prices almost always exclude the battery bank and inverter. Those are frequently the most expensive parts of the system — a quality lithium bank can cost more than the panels, charge controller, and wiring combined. When you see a headline price for a “complete solar kit,” look carefully at what’s actually in the box before comparing it to an all-in quote.

The One Thing to Carry Out of Here

Don’t start with panel count. Start with your daily watt-hour load, size your battery to hold a night’s worth of it, then size your panels to refill that battery in a reasonable day of sun — using 5 peak hours and a conservative harvest figure, not the nameplate. A 100W panel delivers roughly 300–400 Wh per day in practice, flat-mounted panels give up another meaningful chunk, and the battery is almost always the binding constraint. Get the storage right first. The panels are just the pump that fills it tomorrow.