How much solar and battery to run a washing machine in a sailboat?
A washing machine spikes hard on the spin cycle. In a sailboat in the UK it uses about 500 Wh a day. Wattonomy sizes the battery (5.12 kWh), the solar (400 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 sailboat running a washing machine
System
24 V
Battery
5.12 kWh
Solar
400 W
Inverter
MP-II 24/5000
SmartSolar 100/201×
200W solar panel2×
Battery → inverter cable7×
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
The spin-motor surge is the catch.
A washing machine’s daily energy is modest, but the spin motor can spike about 2,200 W. The inverter and cable must carry that surge without faulting. Wattonomy sizes the bank, solar and every cable around it, to BS 7671.
What it takes to run a washing machine
Real numbers from a sized sailboat build for the UK, not rules of thumb.
Daily energy
About 500 Wh a day for the washing machine itself, the figure everything else is sized from.
Battery
About 5.12 kWh of LiFePO4 (roughly 213 Ah at 24V) 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.
Inverter and surge
Sized to start the 2200 W surge cleanly: MultiPlus-II 24/5000, with cable to match, to BS 7671.
What you walk away with — free
A full system sized to run your washing machine — 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 washing machine use?
A washing machine runs at about 500 W and can surge to roughly 2200 W on start-up, using around 500 Wh over a day. The inverter has to cover that surge, not just the running watts.
What size battery runs a washing machine in a sailboat?
For this build Wattonomy sizes about 5.12 kWh (roughly 213 Ah at 24V) of LiFePO4 — enough to carry the washing machine 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 washing machine?
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 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