Last updated: October 22, 2026
Most van lifers end up with somewhere between 200 and 600 watts of solar, and the right figure for you comes from your daily energy use, not from the roof space available. The formula is straightforward: divide your daily watt-hours by the peak sun hours at your location and by about 0.75 to allow for real-world losses. A van using 1,000 Wh a day under 4 sun hours needs roughly 330 W. The sections below walk through each step and a quick way to sanity-check the result.
- Step 1: add up your daily watt-hours
- Step 2: find your peak sun hours
- Step 3: apply the efficiency factor
- Worked example: a remote worker in a mid-size van
- Step 4: check roof space and the rest of the system
- Solar or driving charge: where each fits
- Common myths about van solar
- A quick way to sanity-check your result
- Safety and when to get help
- Related guides
- Frequently asked questions
Step 1: add up your daily watt-hours
Solar is sized against energy, not against appliance wattage. List each device, multiply its power draw by the hours it runs, and add the results. A compressor fridge, lights, a vent fan, phone charging and a few hours of laptop use commonly land between 600 and 1,200 Wh a day. Adding a coffee maker, induction hob or air conditioner can double that or more.
Be honest about habits. Charging a laptop for eight hours of remote work is a very different load from checking email once. Many people also find a more efficient laptop trims the total noticeably; the AMD laptop roundup discusses battery life if that matters for your setup.
Step 2: find your peak sun hours
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A peak sun hour is one hour of sunlight at 1,000 W per square meter. It is a way of expressing how much usable sun a day delivers. Across the continental United States, annual figures are commonly in the range of about 3.5 to 6 hours, higher in the Southwest and lower in the Pacific Northwest and Northeast, with winter values often a half to a third of summer values.
Do not size for your best month. Size for the season you plan to travel in, and look up your region’s averages using published solar resource maps. If you will chase sun, a summer-based number is fine; if you winter in the north, assume 2 to 3 hours.
Step 3: apply the efficiency factor
Panels rarely deliver their label rating. Heat, dust, wiring loss, charge-controller loss, imperfect tilt (roof panels lie flat) and partial shade all take a share. A factor of 0.7 to 0.8 is commonly used, and 0.75 is a reasonable middle. So the formula becomes: panel watts needed = daily Wh ÷ (sun hours × 0.75).
| Daily use | 3 sun hours | 4 sun hours | 5 sun hours |
|---|---|---|---|
| 500 Wh | about 220 W | about 170 W | about 130 W |
| 1,000 Wh | about 440 W | about 330 W | about 270 W |
| 1,500 Wh | about 670 W | 500 W | 400 W |
| 2,000 Wh | about 890 W | about 670 W | about 530 W |
These figures cover the full daily load. If you also expect alternator charging while driving, you can reasonably size the array a little lower.
Worked example: a remote worker in a mid-size van
Assume a fridge averaging 25 W (600 Wh a day), lights and fan totaling 100 Wh, phones and a router at 100 Wh, and a laptop at 60 W for 4 hours (240 Wh). The total is 1,040 Wh. With 4 sun hours and the 0.75 factor, that needs 1,040 ÷ 3 ≈ 347 W, so three 120 W panels (360 W) fit nicely. In a 2.5-hour winter scenario the same load needs about 555 W, which is why this owner would pair solar with a DC-DC charger. For that wiring, see the guide on wiring a DC-DC charger.
Step 4: check roof space and the rest of the system
A typical 100 W rigid panel is roughly 4 feet by 1.7 feet, though sizes vary by brand, so check the datasheet. A van roof also holds a vent fan, an air conditioner or a rack, which can leave less room than you think. Measure the usable area, add room for cable entry and mounting, then see how many panels truly fit.
- Charge controller: divide array watts by battery voltage and add a margin of about 25 percent. A 400 W array on a 12 V system suggests a controller rated near 40 to 50 A. Confirm the maximum PV voltage too.
- Battery capacity: panels fill the battery only if it has room. Many builders aim for at least one to two days of storage.
- Wiring and fusing: panel strings, controller output and battery cable each need correctly rated fuses or breakers.
- Shading: a single shaded panel in a series string can cut output sharply.
Solar or driving charge: where each fits
Solar and alternator charging cover different gaps. Panels work while you are parked, which suits long stays at one camp, but they depend on weather, season and shade. A DC-DC charger works whenever the engine runs, so it suits people who drive most days and need dependable energy in dark months. Many vans use both, and that combination lets you size the array for average conditions instead of the worst day of the year.
If you drive for an hour a day, a 30 A DC-DC charger can move up to roughly 30Ah into the battery in that hour in the best case, which is around 380 Wh, though real rates are often lower because alternator output and battery temperature limit the flow. Compared with the example above, that is about a third of a typical day’s use from a short commute alone.
Common myths about van solar
More watts does not make charging happen at night, and panels generate less on cloudy days and when the roof is dirty or snow-covered. Panel wattage also does not need to match battery amp-hours; a 100Ah battery and a 400 W array are both reasonable if your loads justify them. Finally, the controller, not the panel, sets the charging profile, so a cheap unit can waste an otherwise good array. Another frequent assumption is that tilting is unnecessary: flat roof panels are convenient, but in winter at northern latitudes a flat panel can lose a meaningful share of output compared with a tilted one, which is one more reason to leave headroom in your target.
A quick way to sanity-check your result
Once you have a number, ask three questions. First, can the roof physically hold that many panels alongside its vents and rack? Second, does the battery have the capacity to store a full day of production, remembering that a 100Ah, 12 V battery holds about 1,200 Wh of nominal energy, and only part of that is usable? Third, does the answer still work in the season you actually travel? If any answer is no, reduce loads before adding panels, because every watt-hour you avoid using is a watt-hour you never have to generate.
Safety and when to get help
Panels produce voltage whenever light hits them, and there is no off switch on the panel itself. Cover them or use a disconnect while wiring, and never work on live connections. Roof penetrations must be sealed with a sealant intended for vehicle use, or leaks can damage the van over time. Follow every manufacturer’s instructions, and ask a qualified installer to check your work if you are unsure about fusing, cable sizing or grounding.
Related guides
- How Long Will A 100Ah Battery Last In A Van
- Maxxfan Deluxe Vs Fantastic Fan For Vans
- Van Awning For Campers
Frequently asked questions
Is 200 watts of solar enough for a van?
For light use, often yes. Using the common estimate of panel watts times peak sun hours times about 0.75, 200 W under 4 sun hours yields roughly 600 Wh a day. That can cover lights, a small compressor fridge, fans and device charging. It will fall short for heavy remote work, electric cooking or air conditioning, and winter output can be far lower.
Can solar alone run a van fridge?
In sunny seasons it often can, provided the battery is large enough to carry the fridge overnight and the panels are not shaded. A compressor fridge may use several hundred watt-hours a day, which a modest array can supply. In winter, at higher latitudes or in forest camping, many people add driving charge from the alternator as a backup.
Should you wire van solar panels in series or parallel?
It depends on the charge controller and the shading you expect. Series wiring raises voltage and uses thinner cable, but one shaded panel can drag down the whole string. Parallel keeps voltage low and handles partial shade better, but carries more current. Always check the controller’s maximum input voltage and current in its manual before choosing.
Do you need MPPT, or is PWM good enough?
MPPT controllers generally extract more energy, especially in cold or low light and when panel voltage is well above battery voltage, so they are the usual choice for larger arrays. PWM controllers are simpler and cheaper and can be adequate for one or two small panels matched to a 12 V battery. Compare the specifications and your array size.
Does solar work on cloudy days?
Yes, but at a fraction of its rated output. Heavy cloud can cut production dramatically, sometimes to a small share of what a clear day gives. This is why sizing guides use conservative peak sun hour figures and why many vans also carry a DC-DC charger. Plan for your worst regular season rather than your best day.
