How many solar watts do you need for a van?
Work it out from what you use each day and how much sun you get, not from a rule of thumb.
Step 1: Add up daily energy (Wh)
For each device, multiply watts by hours used per day, then add them. Use the device label or a meter. Example: a 60 W device for 5 hours is 300 Wh; add a 20 W light for 4 hours (80 Wh), and the day totals 380 Wh.
Step 2: Find your peak sun hours
"Peak sun hours" is the daily solar energy at your location expressed as hours of full sun. It changes with place, season, tilt and shading, and it is much lower in winter. The national lab NLR (formerly NREL) offers the free PVWatts calculator, which estimates output for a location and panel tilt.
Step 3: Divide and add margin
Panel watts ≈ daily Wh ÷ peak sun hours, then add margin for real-world losses (heat, dirt, wiring, controller, flat-mounted panels and shade).
| Daily use | If your site gets 3 peak sun hours | If it gets 5 |
|---|---|---|
| 380 Wh | About 127 W before margin | About 76 W before margin |
| 1,000 Wh | About 333 W before margin | About 200 W before margin |
The sun-hour values are examples for the arithmetic, not data for any place. Use PVWatts for your location.
Step 4: Check roof space and the battery
Your roof may limit how many panels fit; portable panels can add more and be moved out of shade. The battery has to hold enough for nights and cloudy days, and the charge controller must be rated for the array's voltage and current. Battery sizing math: Power basics.
Van solar calculator
Example rows are made-up round numbers to show the method, not measurements. Replace them with the watts on your own device labels. Runs in your browser; nothing is sent anywhere. The 3 sun hours and 25% losses are example settings, not data for any place; use PVWatts for your location and season. Need the battery too? Try the house battery calculator.
| Device | Watts | Hours per day | How many | Wh per day |
|---|
Estimates only. Actual output varies.