Solar for camper vans

A high-roof cargo van has roughly 40–60 square feet of usable roof once you subtract the fan, a roof rack, and any vent or awning hardware. That’s two to four residential-format panels or a handful of narrow RV panels: 200 W is a common compromise, 400 W is a full roof, and 100 W is what fits when the roof is mostly rack and box. Flat-mounted at Colorado latitude, expect roughly 4–5 kWh per kW per day in summer and 1.5–2.5 in winter, so a 200 W roof makes about 0.8–1 kWh on a good June day and 0.3–0.5 kWh in January.

That’s enough to run a 12-volt compressor fridge (typically 0.4–0.8 kWh a day), a roof fan, LED lights, and phone and laptop charging indefinitely in summer. It is not enough for induction cooking, an electric heater, or air conditioning. Those loads are what the alternator and a large battery are for, and even then they need honest arithmetic.

A DC-DC charger between the starter battery and the house bank pushes 20–60 amps while the engine runs, which at 12 volts is 250–700 W — more than the entire roof, available on the drive from Denver to Buena Vista whether it’s sunny or not. Two hours of driving with a 40-amp charger deposits close to 1 kWh. On a van that moves every day or two, that is the majority of the energy budget.

Solar fills the gap on the days the van sits: a weekend at a campground, a week of working from a trailhead. Sizing rule of thumb: pick the battery for two or three days of your real loads, pick the DC-DC charger for how many hours you drive, and then let solar be whatever the roof allows. Builders who start from the solar number and work backward tend to end up with an undersized battery and a disappointing first winter.

A folding 100–200 W panel that you set on the ground and tilt toward the sun can out-produce the roof, because you park the van in the shade and put the panel in the sun, and because a tilted panel in December catches far more than a flat one. Rough market prices run $100–$400 depending on quality, and prices vary. The trade-offs are theft, wind, and the ten minutes of setup that many people stop doing after the first month.

For Colorado winter camping, tilt matters more than wattage. A panel tilted to roughly 60 degrees in January catches the low sun; the same panel flat on the roof under a dusting of snow catches nothing. If you camp year-round, a portable panel with a real cable and a weatherproof plug on the van is a better second purchase than another roof panel.

Elevation helps the panels — stronger sun through thinner air, cooler cells — and hurts the battery. Lithium iron phosphate cells should not be charged below about 32°F. Most quality batteries either include a heater that runs from the charge source or a cutoff that simply refuses the charge until the cell warms. Discharging in the cold is fine down to well below zero, though capacity drops somewhat, so an insulated battery box inside the living space rather than under the floor solves most of the problem.

Two other altitude realities: propane and gasoline heaters lose some output in thin air, which pushes people toward electric heat they cannot support, and clear high-country nights radiate heat fast, so a well-insulated van matters more than a bigger battery. Plan the thermal side first; electrical problems in Colorado vans are usually heat problems in disguise.

The common load list: a 12-volt fridge, a roof fan, lights, a diesel or propane heater’s fan and igniter (small but continuous on winter nights), a laptop and phones, and increasingly a satellite internet dish, which draws a surprising 50–100 W continuously — 1–2 kWh a day by itself, and the single most common reason a 200 W roof suddenly feels small. Induction cooktops and electric water heaters are possible with a 3–5 kWh bank and a strong alternator setup, but they move the build into a different budget tier, roughly $3,000–$8,000 in parts for a complete system, and prices vary a lot.

If the van lives at your house between trips, a weatherproof 15- or 20-amp outlet at the parking spot keeps the bank charged and the fridge cold through shore power. Solar on the house offsets that draw under net metering, and if you eventually want a 240-volt outlet for a plug-in vehicle, we can scope that alongside a rooftop system or EV charger. The van’s own wiring stays with a van builder.