RV & Van Solar Sizing Calculator

It depends entirely on what you run and where you travel. A weekend camper with lights, a phone, and a fan might get by with 200W. A full-timer with a 12V fridge, laptop, and CPAP typically needs 400–600W.

The calculator above gives you a precise number based on your actual appliance list — it already builds in a 0.8 efficiency factor to cover real-world losses (heat, wiring, MPPT). When buying equipment, round up to the next available panel size for additional headroom.

Most van builds land between 100Ah and 200Ah at 12V. The right size depends on three things: how much energy you use per day, how many cloudy days you want to survive without shore power, and what battery chemistry you choose.

Lithium (LiFePO4) is the best value for vans — it's lighter, you can safely use 80% of its rated capacity, and it handles partial charges without damage. AGM costs less upfront but you can only use 50% before damaging it, so you effectively need twice the rated capacity to get the same usable storage.

Peak sun hours are not the same as daylight hours. One peak sun hour equals 1,000 watts of solar energy per square meter — the equivalent of full midday sun for one hour. A location with 5 peak sun hours receives the same total solar energy as 5 hours of that perfect midday intensity, spread across the day.

The US average is around 4–5 hours. The Southwest (Arizona, Nevada, New Mexico) gets 6–7. The Pacific Northwest and Alaska get 3–4. Select your state above and the calculator fills this in automatically from NREL data.

For most RV and van builds: MPPT. It's more efficient (up to 30% more harvest in low-light conditions), handles higher panel voltages, and pays for itself quickly when paired with lithium batteries.

PWM is only worth considering for very small systems under 200W with a tight budget. The moment your panel voltage exceeds your battery voltage — which is common with modern panels — PWM wastes the difference. MPPT converts that excess voltage into extra current instead.

Higher voltage means lower current for the same power, which lets you use thinner (cheaper) wire and reduces losses over long cable runs. The tradeoff is that your appliances, inverter, and charge controller must match your system voltage.

12V is the standard for RVs and vans. Most 12V appliances, lights, and accessories are plug-and-play. 24V makes sense above ~600W where wire sizing becomes expensive. 48V is for large off-grid cabins and whole-house systems — rarely worth the complexity in a vehicle.

The formulas are standard electrical engineering — the same ones professional installers use. Accuracy depends mostly on your inputs: real appliance wattages (check the label or a Kill-A-Watt meter) and honest daily usage hours.

The 0.8 efficiency factor accounts for real-world losses: panel temperature derating, wiring resistance, charge controller efficiency, and non-ideal sun angles. We recommend sizing up by 20% when buying equipment to build in practical headroom.