How to design solar for a van or RV
Roof space is fixed, and in winter two of your three charging sources disappear together.
Vehicle solar is constrained differently from a house. The roof is small and fixed, the panels are flat rather than tilted, and there is usually shore power and an alternator as well.
Step-by-step
- List your loads — fridge, lights, water pump, charging, heating fan.
- Enter your usable roof area.
- Enter where and when you travel.
- Read the array and battery required.
The winter problem
In summer the panels do most of the work. In winter three things happen together: solar output falls sharply, the flat mounting costs more than it does in summer because the sun is low, and you are parked up rather than driving, so the alternator is not charging either.
People size for a summer trip, find it works beautifully, and discover in November that the system supports roughly a day. Plan for the season you will actually use.
Flat panels lose more than you expect
A roof-mounted panel lies flat. In summer with a high sun that costs little; in winter, when the sun is low, a flat panel receives a small fraction of what a tilted one would. The seasonal swing is considerably worse than for a house array on a pitched roof.
Refrigeration dominates
In most vans the fridge is the largest single load, running continuously and drawing more in hot weather — precisely when you are least likely to move the vehicle. Size around it first; everything else is comparatively minor.
Three charging sources
- Solar — free, and seasonal.
- Alternator via a battery-to-battery charger. Substantial, and only while driving.
- Shore power — reliable, and only at a site.
A realistic design uses all three and does not depend entirely on any one. A system that works only while driving is not much use on a week's stay, and one that depends on hookup defeats the purpose.
Frequently asked questions
How much solar fits on a van roof?
Usually 200–600 W depending on the vehicle and what else is up there. Roof area is the binding constraint, which is why load reduction matters so much.
Why does my system struggle in winter?
Solar output falls, the flat mounting costs more when the sun is low, and being parked rather than driving removes alternator charging. All three coincide.
What uses the most power in a campervan?
Refrigeration in nearly every case. It runs continuously and draws more in hot weather. Size the system around it before considering anything else.
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