Off-grid by project · RVs and vans
RV and van solar: how to size a 12V system
A van or RV runs on a small battery, limited roof space, and whatever sun you park in. Here's how to size panels, batteries and an inverter for how you actually travel.
At a glance
Two example builds
These use typical values from the appliance wattage chart, 200 W panels, and the same sizing math as the off-grid planner.
Weekend van: 0.96 kWh a day
| Conditions | 200 W panels | Battery (1 day) | Battery (2 days) |
|---|---|---|---|
| 5 sun hours (sunny summer) | 2 (0.4 kW) | 1.44 kWh ≈ 2 × 12V 100Ah | 2.87 kWh ≈ 3 × 12V 100Ah |
| 3 sun hours (winter or shade) | 3 (0.6 kW) | 1.44 kWh ≈ 2 × 12V 100Ah | 2.87 kWh ≈ 3 × 12V 100Ah |
Inverter: none needed. Every load here runs on 12V DC.
Full-time van with remote work: 2.72 kWh a day
| Conditions | 200 W panels | Battery (1 day) | Battery (2 days) |
|---|---|---|---|
| 5 sun hours (sunny summer) | 5 (1.0 kW) | 4.07 kWh ≈ 4 × 12V 100Ah | 8.16 kWh ≈ 7 × 12V 100Ah |
| 3 sun hours (winter or shade) | 7 (1.4 kW) | 4.07 kWh ≈ 4 × 12V 100Ah | 8.16 kWh ≈ 7 × 12V 100Ah |
Inverter: the 120V loads total 125 W, so a small pure sine inverter rated 157 W or more covers them (small units start around 300 W). Size up if you add a microwave, kettle or hair dryer.
Roof space is the real limit
Many camper vans fit roughly 400–800 W of rigid panels once vents and racks are accounted for; larger RVs fit more. The full-time example needs 7 × 200 W (1.4 kW) in low sun, which most vans can't carry. Close the gap with:
- A DC-DC charger: recharges the house battery while you drive and protects the alternator.
- Portable panels: park in shade and put the panels in the sun.
- Shore power: an inverter/charger tops up the battery at campgrounds.
- Lower loads: satellite internet running 24 hours is often the biggest single load; turn it off overnight.
- Roof panelsCharge in daylight
- Solar charge controllerMPPT, sized to the array
- 12V batteryFused at the positive post
- 12V fuse blockOne fuse per circuit
- 12V loadsFridge, fan, pump, lights, USB
Two more connections attach directly to the battery, not to this chain: a DC-DC charger that recharges it from the alternator while you drive, and an inverter (on its own fuse) for 120V devices. Shore power wiring belongs to an RV electrician.
Size your own van or RV system
- Daily use
- 0.96 kWh
- Battery (1 day)
- 1.44 kWh
- Inverter
- Not needed
- Startup surge
- 12V loads only
Uses the same math as the off-grid planner at 5 peak sun hours. A planning estimate, not a design.
12V first, inverter second
Every watt that runs on 12V DC avoids inverter losses and idle draw. Choose a 12V compressor fridge, 12V fans and pump, and USB-C charging where you can. Use the inverter only for true 120V devices, and switch it off when you don't need it. See the inverter sizing guide if you plan to run high-power appliances.
Vehicle-specific safety
- Fuse at the battery. Put a properly rated fuse within inches of the battery positive, and fuse every branch circuit.
- Secure the battery. Batteries must be strapped down to survive a hard stop or crash.
- Protect lithium from cold charging. A parked rig can get as cold inside as out, so cabin placement alone isn't enough. Follow the battery's rated charging temperature range (many LiFePO4 batteries can't be charged below about 32°F / 0°C), and use a battery with a low-temperature charge cutoff, self-heating, or a BMS that can switch off the solar and DC-DC chargers when the cells are too cold.
- Rate mounts for highway wind. Seal every roof penetration and use hardware rated for the speeds you drive.
- Use marine-grade, fine-stranded cable. Vibration breaks solid wire over time.
- Get shore-power wiring checked. Connecting 120V shore power to an inverter/charger and outlets is a job for an RV electrician. See what's safe to DIY.
FAQ
How many solar panels do I need for a van?
A weekend van with a 12V fridge, fan, lights and phone charging often needs about 400–600 W of panels. Full-time living with a laptop and satellite internet can need well over 1,000 W, which is more than many van roofs hold, so alternator charging fills the gap.
What size battery do I need for an RV or van?
Start with one day of your daily watt-hours, then add more if you camp in shade or cloudy weather. Many vans land between two and four 12V 100Ah lithium batteries (about 2.6–5.1 kWh).
Do I need an inverter in my van?
Only for 120V devices. 12V fridges, fans, pumps, lights and USB charging run straight from the battery. If you only charge a laptop and phone, a small pure sine inverter is enough; a microwave, kettle or hair dryer needs 1,500 W or more.
Can I charge my van battery from the alternator?
Yes, through a DC-DC charger. It protects the vehicle's alternator and charges lithium batteries at the correct voltage. Wiring it straight across without one is not recommended.
Is 12V or 24V better for a van?
12V suits most vans because vehicle accessories are 12V. Larger RVs with big inverters may benefit from 24V or 48V to keep current and cable size down.