At a cabin you can’t drive to the sun. Wattonomy sizes for the overcast days — more battery, more autonomy, residential panels — checks the cold-weather details winter starts trip on, and gives you the wiring and parts to build it.
Wire & fuse sizes follow NEC — each conductor carries its fuse and stays under a 3% voltage drop.
Built to NEC & NFPA standards
Gauge · fuse · volt-drop sized
Every spec sourced
Off-grid, the real risk is a dark January.
Size for the annual average and you’ll be cold and dark in the worst week of winter; oversize blindly and you’ve overspent by thousands on panels and batteries you didn’t need. Wattonomy sizes to your days of autonomy and worst-case sun, so you get the cheapest system that actually keeps the lights on.
How off-grid sizing works
Off-grid systems live or die on autonomy and honest winter numbers — where most kits get it wrong.
Days of autonomy
3–5 days of backup for cloudy stretches — the single biggest driver of how much battery you carry.
Worst-case sun
We size to your climate’s low-production months, not the summer best case, so winter doesn’t catch you out.
24V or 48V bank
Higher voltage for whole-cabin loads means thinner copper and less loss — we pick and size it for you.
Wiring & protection
Every conductor and breaker sized for ampacity and voltage drop over your real runs, to NEC / NFPA.
What you walk away with — free
A bank + array sized to your worst-case winter month
A wiring diagram with breaker and conductor sizing
Voltage-drop checked over your real cable runs
A vendor-neutral parts list — no overpriced kit markup
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 cabin
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
Will it size for winter, not just summer?
Yes — sizing is driven by your days of autonomy and the low-production season for your climate, so the system holds through cloudy stretches.
12V, 24V or 48V?
For cabin loads the tool will generally move you to 24V or 48V to cut losses and copper cost, and sizes everything for that voltage.
Is this cheaper than buying a kit?
The parts list is vendor-neutral and sized to exactly what you need — no padding. You buy the components wherever you like; we just make sure they’re right.
Do I need an account?
No. Design free with no email required; accounts are only for saving builds or the 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.
NECThe US National Electrical Code — the rulebook for fixed building wiring.
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 / NEC. 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