Knowing your local peak sun hours is the foundation of sizing a van or RV solar system correctly. Use this reference when planning your build.
What peak sun hours (PSH) mean
Peak sun hours aren't total daylight hours — they're the equivalent number of hours at full-strength sun (1,000 W/m²). A location with 4 PSH receives the same total solar energy as 4 hours of perfect noon sun, even if actual sunlight lasts 10–14 hours at lower intensities.
Formula for daily solar output: Panel watts × PSH × 0.75 (system efficiency) = Wh/day
Example: 400W × 4.5 PSH × 0.75 = 1,350Wh/day
PSH by region (annual average / winter minimum)
Southwest — Best solar in the US
| City | Annual avg PSH | Winter (Dec-Jan) |
|---|---|---|
| Phoenix, AZ | 6.0 | 4.5 |
| Las Vegas, NV | 6.2 | 4.8 |
| Tucson, AZ | 6.3 | 4.7 |
| Albuquerque, NM | 6.0 | 4.5 |
| El Paso, TX | 6.3 | 5.0 |
| Los Angeles, CA | 5.6 | 4.2 |
Implication: A 300W system handles most full-time van loads year-round in the Southwest. The desert is a reliable solar destination for winter camping.
Mountain West — Good solar, altitude helps
| City | Annual avg PSH | Winter (Dec-Jan) |
|---|---|---|
| Denver, CO | 5.5 | 4.0 |
| Salt Lake City, UT | 5.3 | 3.5 |
| Boise, ID | 4.8 | 2.5 |
| Helena, MT | 4.5 | 2.5 |
Implication: Denver and SLC are excellent for solar. Northern Montana and Idaho have challenging winters — plan for 200Wh/day production on bad January days.
Southeast & South — Consistent year-round
| City | Annual avg PSH | Winter (Dec-Jan) |
|---|---|---|
| Miami, FL | 5.3 | 4.5 |
| Orlando, FL | 5.1 | 4.2 |
| Atlanta, GA | 4.7 | 3.5 |
| Dallas, TX | 5.3 | 3.8 |
| Nashville, TN | 4.4 | 2.8 |
| New Orleans, LA | 4.8 | 3.5 |
Implication: Florida is exceptional for year-round solar. The upper Southeast drops in winter but remains viable with adequate panel sizing.
Mid-Atlantic & Northeast — Seasonal planning required
| City | Annual avg PSH | Winter (Dec-Jan) |
|---|---|---|
| New York City, NY | 4.1 | 2.5 |
| Philadelphia, PA | 4.2 | 2.8 |
| Boston, MA | 4.0 | 2.5 |
| Washington DC | 4.2 | 2.9 |
| Pittsburgh, PA | 3.8 | 2.2 |
Implication: Northeast winters require aggressive supplemental charging. Plan for 2–3 PSH in January and rely heavily on DC-DC alternator charging during winter months.
Midwest — Average with harsh winters
| City | Annual avg PSH | Winter (Dec-Jan) |
|---|---|---|
| Chicago, IL | 4.1 | 2.3 |
| Minneapolis, MN | 4.3 | 2.0 |
| Detroit, MI | 3.9 | 2.0 |
| Kansas City, MO | 4.8 | 3.2 |
| Columbus, OH | 4.0 | 2.2 |
Implication: Upper Midwest winters are the most challenging in the country for solar. Minneapolis in January gets ~2 PSH on clear days — and many days aren't clear. Full-time van lifers overwintering here need large batteries and aggressive alternator charging strategy.
Pacific Northwest — The solar challenge region
| City | Annual avg PSH | Winter (Dec-Jan) |
|---|---|---|
| Seattle, WA | 3.5 | 1.5 |
| Portland, OR | 3.6 | 1.8 |
| Eugene, OR | 3.8 | 1.8 |
| Bend, OR | 4.5 | 2.5 |
Implication: The wet Pacific Northwest coast is genuinely hard for solar. Seattle in January can go 1–2 weeks with under 1 PSH per day. Bend (east of the Cascades) is significantly better. Pacific Northwest van lifers should plan for DC-DC and shore power as primary charging in winter, solar as summer supplement.
How to use this for sizing
Step 1: Find the PSH for your typical camping region (use the winter value if you camp in that region in winter).
Step 2: Calculate your daily Wh consumption.
Step 3: Watts needed = Daily Wh ÷ (PSH × 0.75)
Example (Seattle winter): 800Wh/day ÷ (1.5 × 0.75) = 711W of solar needed — which is a lot of roof space. In this case, plan for solar in summer and drive/shore-charge in winter instead.
Example (Phoenix winter): 800Wh/day ÷ (4.5 × 0.75) = 237W — a 300W system handles it comfortably.
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