200W vs 400W Solar for a Van or RV: What's the Right Size?
200W vs 400W is one of the most common solar sizing debates in van builds. Here's how to decide which you actually need.
Real-world output numbers
Rated panel wattage assumes perfect conditions (1,000 W/m², 25°C, direct perpendicular sun). Real-world output accounts for angle, heat, inverter efficiency, and wiring losses. A practical multiplier is 0.75 of rated wattage per peak sun hour.
| System | 4 PSH (average US) | 5.5 PSH (Southwest) | 2 PSH (PNW winter) |
|---|---|---|---|
| 200W | ~600Wh/day | ~825Wh/day | ~300Wh/day |
| 400W | ~1,200Wh/day | ~1,650Wh/day | ~600Wh/day |
Daily power consumption benchmarks
| Lifestyle | Daily Wh | Notes |
|---|---|---|
| Minimalist van weekend | 200–350Wh | Fridge, phone, lighting |
| Standard full-time | 500–800Wh | Above + laptop, fan |
| Heavy user full-time | 900–1,400Wh | Above + desktop, more screens |
| Induction cooking regularly | Add 400–800Wh/day | One induction cook = 1,000–2,000W for 20–30 min |
When 200W is enough
- Weekend van use: 600Wh/day easily covers a weekend load in most US conditions.
- Full-time in the Southwest or Southeast in summer: A 200Ah LiFePO4 battery tops up in 3–4 hours of good sun and stays there.
- Minimal loads: If you're mostly driving, working at libraries, and not running a dedicated laptop setup, 200W is fine.
- Budget constraints: 200W of solar + quality MPPT is achievable under $250. 400W pushes $400–500 for the panels alone.
When 400W makes more sense
- Full-time van life in variable sun regions: More panel capacity buffers cloudy days and early morning/late afternoon low-angle sun.
- High power loads: A dedicated work-from-van setup with a laptop, monitor, and frequent charging needs may consistently draw 700–1,000Wh/day.
- Stationary camping periods: If you park for multiple days without driving, more solar means more independence from shore power.
- Cold climates in winter: A diesel heater may require 30–50Wh to start but a heater fan running overnight adds 100–200Wh — extra solar helps in northern winters.
The battery size connection
Solar and battery are a system. A general guideline:
- 200W solar → 100–200Ah battery (charges in 1–3 days from empty)
- 400W solar → 200–300Ah battery (good match for full-capacity recharge in 1–2 days)
Oversizing solar relative to battery means you often hit float charge by noon — extra panels go unused. Undersizing means the battery slowly drains over several cloudy days. Balance them.
200W + DC-DC charging vs 400W solar
An alternative to a large solar array: 200W of solar plus a quality 40–60A DC-DC charger. The DC-DC adds 200–300Ah per travel day from the alternator.
For builders who drive frequently (touring, traveling rather than stationary camping), this combination often makes more practical sense than 400W of roof panels that only help when parked.
The simple decision framework
- Calculate your daily Wh — see how many watts your van uses per day
- Look up your typical PSH — see peak sun hours by state
- Use the formula: Solar watts = Daily Wh ÷ (PSH × 0.75)
If the answer is under 250W → 200W system is fine. If the answer is 250–450W → 400W is the right target. If the answer is 450W+ → consider 400W solar + DC-DC charging or 600W if you have the roof space.