Solar for a camper van

Most camper van electrical systems start from a short list: a 12 V fridge, a fan, lights, a water pump and phones. Add a laptop and internet and it becomes a full-time setup. The sizes below come from the RVWatt weekender and full-time van presets, with NASA sun data for a flat roof and default MPPT plus LiFePO4 losses (system factor 0.757).

Weekend van, 830 Wh a day

The weekender preset is a 50–65 L 12 V fridge (432 Wh), roof fan (240 Wh), LED lights (80 Wh), water pump (18 Wh) and two phones (60 Wh). That is 830 Wh a day, all DC, so no inverter is required. The preset uses two days of lithium backup (80% usable) and sizes solar to the weakest month you travel.

Place and season	Design month	Solar needed	Array (200 W panels)	Battery at 12 V	Controller
Moab, UT, May–October	October, 4.34 sun hours	253 W	2 × 200 W (400 W)	173 Ah (2,075 Wh)	50 A MPPT
Denver, CO, May–October	October, 3.98 sun hours	276 W	2 × 200 W (400 W)	173 Ah (2,075 Wh)	50 A MPPT
Seattle, WA, May–October	October, 2.28 sun hours	481 W	3 × 200 W (600 W)	173 Ah (2,075 Wh)	70 A MPPT

A common 400 W / 200 Ah lithium kit covers the Moab and Denver cases with some room (173 Ah is the two-day number; a 200 Ah bank is the usual product size). In Seattle that same season you need closer to 600 W of panels because October only has 2.28 peak sun hours on a flat roof. Record lows below freezing have been logged in May and October in all three cities, so if you may camp through a cold night, use a self-heating battery or keep the bank inside.

Open the weekender van in Moab, May–October Same van in Seattle

Full-time van, about 2,103 Wh a day

The full-time preset keeps the weekender loads and adds a laptop for six hours (433 Wh from the battery), a Starlink Mini for eight hours (240 Wh), a diesel heater for eight hours (120 Wh) and a short induction-cooking session (420 Wh), plus about 60 Wh of inverter idle. That is 2,103 Wh a day. Because of the induction cooktop, the calculator sizes a 2,500 W inverter (1,800 W × 1.25 headroom, rounded up), with a surge rating of at least 1,865 W.

Place and season	Design month	Solar needed	Array	Battery at 12 V
Hailey, ID, July only	July, 7.69 sun hours	361 W	2 × 200 W (400 W)	438 Ah (5.3 kWh)
Hailey, ID, May–September	September, 5.14 sun hours	541 W	3 × 200 W (600 W)	438 Ah (5.3 kWh)
Phoenix, AZ, November–March	December, 3.08 sun hours	902 W	5 × 200 W (1,000 W)	438 Ah (5.3 kWh)
Hailey, ID, year-round, solar only	December, 1.54 sun hours	1,804 W	10 × 200 W (2,000 W)	438 Ah (5.3 kWh)
Hailey, ID, year-round, plus a 30 A DC-DC charger for 1 hour a day	December, 1.54 sun hours	1,511 W	8 × 200 W (1,600 W)	438 Ah (5.3 kWh)

The battery stays at about 438 Ah (5.3 kWh) because two days of use do not depend on the sun. The array does. In a northern Rocky Mountain winter, solar alone wants about 1,800 W — more than most van roofs can hold, and the calculator warns about roof space. Even an hour of 30 A alternator charging only brings that down to about 1,511 W. The lesson is the same one on the homepage: winter van life in the northern Rockies runs on the alternator. Solar is the summer workhorse.

Factory Class B vans often take that idea further: a large lithium bank, a small roof array (sometimes 100–250 W) and a strong second alternator. That is a valid design, but it is not “the solar covers the van.” If you enter year-round travel and leave driving hours at zero, RVWatt will say the factory panel is too small — and it is being honest.

Open the full-time van in Hailey, year-round Same van, May–September only Snowbird season in Phoenix

Frequently asked questions

How much solar does a camper van need?

A simple weekend van using 830 Wh a day needs about 253 W of panels in Moab from May to October, or 276 W in Denver — two 200 W panels in either case — and about 173 Ah of lithium for two days. A full-time van using about 2,103 Wh a day needs about 361 W in a Hailey July, 541 W for May–September, and far more if you stay through a northern winter on solar alone.

Why does year-round travel need so much more solar?

Because the calculator sizes to your weakest travel month, not the yearly average. In Hailey, Idaho a flat panel gets 7.69 peak sun hours in July and only 1.54 in December, so the same 2,103 Wh day jumps from 361 W of solar to 1,804 W. Uncheck the months you do not travel, or add alternator charging.

Do factory Class B vans have enough solar?

Often not, if you expect the roof array to refill the bank by itself. Many factory vans ship a large lithium battery and only 100–250 W of solar, and they rely on a second alternator. That works if you drive; it does not match a year-round, solar-only plan. Enter your driving hours in the calculator before you compare.

Related guides

Safety: high-current DC is dangerous. A 12 V battery bank can deliver thousands of amps into a short circuit, enough to melt tools, weld rings and watches to terminals, ignite insulation and start a vehicle fire in seconds. Lithium and lead-acid batteries can also vent, burn or explode if overcharged, damaged or charged outside their temperature limits. Remove jewelry, use insulated tools, disconnect the battery before working, fuse every positive conductor as close to the battery as practical with a fuse rated for the battery's short-circuit current (often a Class T for lithium banks), use properly crimped lugs and pure copper cable, and secure batteries against movement. If you are not confident, hire a qualified RV or marine electrician. RVWatt provides estimates only; see our Terms of Use.

These figures are planning estimates from typical appliance ratings and NASA monthly sun averages for a flat, horizontal panel. Your real use will differ with heat, shade, dirty panels and how you actually live in the rig. Follow your equipment manuals and have a qualified installer check high-current wiring.