How much solar and battery to run a chest freezer in a sailboat?
A chest freezer holds its cold around the clock. In a sailboat in Europe it uses about 620 Wh a day. Wattonomy sizes the battery (5.12 kWh), the solar (400 W) and every cable around it to ISO 13297, then hands you the wiring diagram and a shoppable parts list.
A real Wattonomy output — a EU sailboat running a chest freezer
System
12 V
Battery
5.12 kWh
Solar
400 W
Inverter
MP 12/1600
SmartSolar 150/351×
200W solar panel2×
Battery → inverter cable4×
Battery → inverter fuse1×
Wire & fuse sizes follow ISO 13297 — each conductor carries its fuse and stays under a 3% voltage drop.
Built to ISO 13297 standards
Gauge · fuse · volt-drop sized
Every spec sourced
A freezer cannot be allowed to thaw.
A chest freezer cycles around the clock and must never lose its cold chain. The bank has to carry it through the night and a cloudy day without dropping too deep. Wattonomy sizes the bank, solar and every cable around it, to ISO 13297.
What it takes to run a chest freezer
Real numbers from a sized sailboat build for Europe, not rules of thumb.
Daily energy
About 620 Wh a day for the chest freezer itself, the figure everything else is sized from.
Battery
About 5.12 kWh of LiFePO4 (roughly 427 Ah at 12V) to carry it through the night and a cloudy day.
Solar to replace it
About 400 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 ISO 13297.
What you walk away with — free
A full system sized to run your chest freezer — battery, solar and inverter
A real wiring diagram with cable gauges and fuses
Cable and fuse sizing with the voltage drop checked, to ISO 13297
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 chest freezer use?
A chest freezer draws about 200 W when running, and because it runs much of the day it uses around 620 Wh. Wattonomy sizes from your real figure, not a rule of thumb.
What size battery runs a chest freezer in a sailboat?
For this build Wattonomy sizes about 5.12 kWh (roughly 427 Ah at 12V) of LiFePO4 — enough to carry the chest freezer 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 chest freezer?
About 400 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 European standards?
Yes. Every cable, fuse and busbar is sized to ISO 13297 using mm², at the 12/24V DC and 230V AC typical of Europe 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.
ISO 13297The international standard for small-craft electrical systems.
EN 1648-2The European standard for 12 V electrics in leisure vehicles.
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 ISO 13297. 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