Winter solar surprises most first-time van builders. The panels work fine — the sun just doesn't cooperate as much. Here's what to plan for.
Why winter solar output drops
1. Fewer peak sun hours
Peak sun hours (PSH) measure the daily equivalent of full-strength sun (1,000 W/m²). In the continental US:
| Region | Summer PSH | Winter PSH |
|---|---|---|
| Southwest (Phoenix, Las Vegas) | 6.0–7.0 | 4.0–5.0 |
| Southeast (Atlanta, Dallas) | 4.5–5.5 | 3.0–4.0 |
| Pacific Northwest (Portland, Seattle) | 4.5–5.5 | 1.0–2.0 |
| Northeast (Boston, NYC) | 4.0–5.0 | 2.0–3.0 |
| Mountain West (Denver, Salt Lake) | 5.5–6.5 | 3.5–4.5 |
A 400W array at 4.5 PSH produces 1,440Wh. At 1.5 PSH it produces 480Wh — a 67% drop with the same equipment.
2. Low sun angle
In December at 45°N latitude, the sun's maximum elevation angle is only 21°. Panels mounted flat on a van roof receive solar radiation at a severe angle — much less energy per square foot than when the sun is overhead. A horizontally mounted panel in Seattle in December may only capture 40–50% of the energy a properly tilted panel would.
3. Snow and overcast
A thin snow layer on panels blocks nearly all output. Thicker cloud cover blocks 70–90% of direct solar. The Pacific Northwest and Northeast winters can have 5–10 consecutive overcast days with minimal solar production.
What cold actually does to solar output
Good news: Solar panel output efficiency improves in cold weather. Panels are rated at 25°C (77°F) standard test conditions. Every 10°C drop below 25°C increases output power by roughly 4%. A panel producing 200W at 25°C might produce 208W at 5°C — same sun, more watts per hour.
The bottom line: Cold doesn't hurt. Low sun and short days do.
Compensating for winter solar
1. Tilt your panels (biggest impact)
A panel tilted toward the sun at optimal angle for winter can produce 30–50% more than the same panel flat on the roof. Options:
- Adjustable tilt mounts: Renogy, AM Solar, and Tycon make tilt brackets for rigid panels. You can angle them from the ground without getting on the roof.
- Portable panels with kickstand: The easiest way to optimize angle, especially for stationary winter camping.
A van builder in Denver tilting panels to 55° in December (matching winter sun angle) gets significantly more output than horizontal mounting.
2. Size up before winter, not after
If you winter camp in low-sun regions, size your solar for winter conditions, not summer. The typical recommendation: multiply your daily Wh needs by the reciprocal of your winter PSH, not your summer PSH.
Winter rule of thumb: plan for 2–3 hours of effective production per day in the northern US, 3–4 in the South.
3. Clear snow promptly
Even 1/4" of snow blocks most panel output. A soft-bristle brush or foam squeegee clears panels without scratching. Keep one accessible on cold trips.
4. Lean on DC-DC charging
In winter, plan to drive more and generate more alternator charge. A 40–60A DC-DC charger can add 200–300Ah per travel day — often more than solar can generate in a northern winter week.
5. Shore power when available
Use campground shore power or public 120V charging when available. A 20A circuit charges 200Ah of LiFePO4 in 4–6 hours.
Should you oversize solar for winter?
If you primarily camp in the Southwest or Southeast in winter — no. The sun angles are reasonable and PSH is adequate.
If you winter camp in the Pacific Northwest, Great Lakes, or Northeast — yes, you'll want 20–40% more solar than a summer calculation suggests, AND plan to supplement heavily with driving and shore power on extended bad-weather stretches.
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