How it's calculated
Panels along = floor((Roof length − 2 × margin + gap) ÷ (Panel length + gap))
Panels across = floor((Roof width − 2 × margin + gap) ÷ (Panel width + gap))
The calculator tries both orientations and shows whichever fits more panels.
Tips for van and RV roofs
- Measure the flat, usable area only: between gutters or rails, and clear of vents, fans and aerials.
- Rigid panels with a mounting frame need a few centimetres of extra clearance; flexible panels need less but run hotter.
- Several smaller panels can make better use of space around a roof vent than one large panel.
- Keep panels where they won't be shaded by a roof box or open fan lid, which can cut a series string's output dramatically.
Frequently asked questions
How many solar panels fit on a van roof?
A long-wheelbase panel van usually takes 3–4 standard 175–200 W panels, around 600–800 W, depending on roof vents and rails.
Is it better to have bigger or smaller panels?
Larger panels cost less per watt and need fewer connections, but smaller panels fit around obstacles better.