How much solar and battery to run a fridge in a off-grid cabin?
A fridge runs around the clock. In a off-grid cabin in the UK it uses about 600 Wh a day. Wattonomy sizes the battery (10.24 kWh), the solar (415 W) and every cable around it to BS 7671, then hands you the wiring diagram and a shoppable parts list.
A real Wattonomy output — a UK off-grid cabin running a fridge
System
48 V
Battery
10.24 kWh
Solar
415 W
Inverter
MP-II 48/3000
SmartSolar 100/201×
415W solar panel1×
Battery → inverter cable4×
Battery → inverter fuse1×
Wire & fuse sizes follow BS 7671 — each conductor carries its fuse and stays under a 3% voltage drop.
Built to BS 7671 standards
Gauge · fuse · volt-drop sized
Every spec sourced
A fridge runs day and night, so it sets the whole system.
A fridge never really stops, so it is usually the biggest steady load in a small build. Undersize the bank and the food is warm by morning; undersize the wire and you have a hazard. Wattonomy sizes the bank, solar and every cable around it, to BS 7671.
What it takes to run a fridge
Real numbers from a sized off-grid cabin build for the UK, not rules of thumb.
Daily energy
About 600 Wh a day for the fridge itself, the figure everything else is sized from.
Battery
About 10.24 kWh of LiFePO4 (roughly 213 Ah at 48V) to carry it through the night and a cloudy day.
Solar to replace it
About 415 W of panel replaces a day’s use in fair sun; poor light or winter wants more, or a second charging source.
Cables and fuses
Every conductor sized to carry its fuse, with the voltage drop checked, to BS 7671.
What you walk away with — free
A full system sized to run your fridge — battery, solar and inverter
A real wiring diagram with cable gauges and fuses
Cable and fuse sizing with the voltage drop checked, to BS 7671
A shoppable parts list, every line traceable to a standard or datasheet
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 build
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
How many watts does a fridge use?
A fridge draws about 45 W when running, and because it runs much of the day it uses around 600 Wh. Wattonomy sizes from your real figure, not a rule of thumb.
What size battery runs a fridge in a off-grid cabin?
For this build Wattonomy sizes about 10.24 kWh (roughly 213 Ah at 48V) of LiFePO4 — enough to carry the fridge plus your basics through the night and a cloudy day. Your exact number depends on how many days of backup you want.
How much solar do I need to run a fridge?
About 415 W of panel replaces a day’s use in fair sun; poor light, winter or shade wants more, or a second charging source such as a DC-DC charger off the engine. The tool sizes it from your climate.
Is this sized to UK standards?
Yes. Every cable, fuse and busbar is sized to BS 7671 using mm², at the 12/24V DC and 230V AC typical of the UK systems. Nothing here is a rule of thumb.
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.
BS 7671The UK IET Wiring Regulations for the 230 V side.
ISO 13297The international standard for small-craft electrical systems.
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 BS 7671. 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