400 watts of van solar — here’s what it really runs.
400W is the sweet spot for most weekend and part-time vanlifers. Wattonomy shows what a 400W array actually powers — fridge, lights, charging, fans — sizes the battery and inverter to match, and hands you the wiring diagram and parts list.
Wire & fuse sizes follow ABYC E-11 — each conductor carries its fuse and stays under a 3% voltage drop.
Built to ABYC standards
Gauge · fuse · volt-drop sized
Every spec sourced
400W only works if the rest of the system matches it.
Panels are the easy part. Too little battery and you’re flat by morning; too small an inverter and it cuts out under load. Wattonomy sizes the bank, inverter and every conductor to your actual 400W setup — to ABYC E-11, with the voltage drop checked — so the whole system holds together.
What 400W of van solar gets you
On a fair day, 400W replaces roughly a fridge-plus-essentials load. Here’s how the pieces fit.
What it runs
Comfortably covers a 12V fridge, LED lighting, phone & laptop charging and a roof fan — the core of a part-time build.
Battery to match
Around 5 kWh of LiFePO4 at 12V carries you through the night and a cloudy morning on an honest depth-of-discharge.
Charging beyond solar
Add DC-DC (charge while you drive) for the stretches when 400W on the roof isn’t quite enough.
Cables & fuses
Every gauge and fuse sized to the load and your run lengths, with the AIC checked — to ABYC E-11.
What you walk away with — free
A full 400W system sized to your appliances — battery, inverter, solar, charging
A real wiring diagram with every cable gauge and fuse
Cable & fuse sizing with the voltage drop checked for your runs
A shoppable parts list, each line traceable to ABYC or Victron specs
Building it for real? Unlock the build binder.
Free gets you a safe, correctly-sized design. The build binder gets you the documents to build it right — and prove it's right.
Printable wiring diagram, yours to keep & tape inside the van
Full parts list, every line sourced
The volt-drop & fusing calculation trail — the "why" behind every spec
The build binder is a one-time unlock — no subscription, no auto-renew.
Questions
Is 400W of solar enough for a campervan?
For a part-time or weekend build — fridge, lights, charging, fans — 400W in fair sun is usually enough, paired with a battery sized to carry the night. For full-time living, big loads or winter use you’ll likely want 600W+ and DC-DC charging. Wattonomy sizes it from your actual appliances so you can see exactly where you land.
How many batteries does a 400W system need?
It depends on your loads and how many days of backup you want, not the panel count. For a typical 400W van the tool sizes around 5 kWh (roughly 400Ah at 12V) of LiFePO4 — but enter your real appliances and it sizes the bank to you.
What can I run on 400W?
A 12V fridge, LED lighting, phone and laptop charging, a roof fan and a water pump sit comfortably within a 400W-plus-battery system. High-draw items like induction cooking, kettles or air-con push you to a bigger array, more battery and often 24V — the tool flags that.
Do I need an account?
No. Design the whole system free, no email. Accounts are only for saving builds or the printable build binder.
The standards we build to
Plain version: these are the recognized rulebooks your design is sized against, so the numbers hold up to a surveyor, an inspector or an insurer.
ABYC E-11The US standard for AC & DC wiring on boats — what a surveyor or insurer actually checks.
Wattonomy applies these standards in its calculations. It is not certified, sponsored or endorsed by ABYC, ISO, NFPA or Victron — it sizes your design to meet what they require, and shows the working.
Sized and checked to ABYC E-11. Last reviewed June 2026 — see the full methodology for the exact rules behind every number and how each design is validated.
Built by anABYC Certified Master Technician