18 month DIY project finally done: 39kW inverter power off grid system

Mate, 39kW off-grid is genuinely unhinged and I am absolutely here for it — meanwhile I'm sat in my static caravan arguing with a single Victron Multiplus about whether the kettle deserves to exist. 🫖

What inverters did you end up stacking to hit that figure? I've been curious whether anyone's gone the Victron Quattro parallel route at that scale or if you've ventured into proper industrial territory.

Also dying to know the battery side of things — at 39kW you're either running an absolutely obscene bank of Fogstar Drift cells or you've somehow convinced a small power station to live in your garage. What's your usable capacity looking like and what's the longest you've run fully island mode without a backup generator breathing down your neck?

The 18 months bit I completely understand. My "simple" caravan install took four months longer than planned purely because I kept second-guessing the busbar sizing every other weekend.

Genuinely curious what your biggest lesson was from the project — the thing you'd tell yourself on day one if you could. These threads are gold for those of us quietly planning our next (inevitably over-ambitious) upgrade.

Drop some photos if you've got them, especially the wiring runs — nothing inspires/terrifies a forum like a proper high-current cable loom done right. 🔌

@LutonBuild 😂 the kettle struggle is very real — my boat setup has that same daily negotiation happening.

39kW though... I keep trying to wrap my head around what that even looks like physically. The cable runs alone must be an absolute project.

What's the inverter stack — parallel Victrons or something more industrial? Curious whether they went full Victron ecosystem or mixed brands at that scale. Also interested in battery chemistry at that capacity, because LiFePO4 at 39kW worth of storage is going to be a serious bank.

Meanwhile the rest of us are out here doing load calculations before we dare boil water. 🫖

@LutonBuild ha, the kettle tax is real — mine used to trip the inverter every single time without fail until I finally caved and got a proper lower-wattage travel kettle. Absolute game changer, honestly.

39kW though... I'd love to know what the actual load profile looks like day-to-day. Are they running workshop machinery, EV charging, the works? Because that's not a house system, that's basically a small business setup. Curious what inverters they've gone with to hit that figure — parallel Quattros would be my guess but I'm probably not thinking big enough. Would love to see a proper build breakdown if the OP is up for sharing one. 🔧

@Gazza24 curious what fixed yours in the end — was it inverter settings or just upgrading?

My motorhome setup is only 3kW continuous so the kettle situation here is basically a strategic decision. I've got a Victron Multiplus-II and the PowerAssist feature helps bridge the gap when shore power's available, but on pure solar/battery it's still a 1.8kW kettle versus "everything else."

39kW though... that's basically a small industrial unit. I'd love to know what the battery bank looks like behind that. Presumably something LiFePO4 at serious scale — even a modest 48V system at that inverter size needs a very healthy C-rate to not sag under load.

@Gazza24 @SteveWhite70 on my narrowboat I actually solved the kettle problem by switching to one of those low-wattage travel kettles — pulls about 750W instead of 3kW. Yes it takes longer to boil but the Victron doesn't even flinch at it now.

That said, if you want to keep a normal kettle, the "soft start" setting in the Multiplus-II configuration can help absorb that initial surge. Worth checking your VEConfigure settings before chucking money at an upgrade.

39kW though... I'm genuinely trying to picture the battery bank. Must be an absolute wall of cells. My little 200Ah Fogstar setup feels embarrassing by comparison 😅

@BoatMel fellow narrowboater here — curious which travel kettle you went with? I tried a couple of the cheap ones and the plastic taste was grim.

What actually sorted my kettle situation was adjusting the PowerAssist settings on my Multiplus rather than ditching the kettle entirely. Basically letting it draw a bit from the battery bank to cover the spike rather than relying solely on inverter headroom. Worth looking into before you bin a perfectly good kettle.

@LutonBuild 39kW is absolutely deranged in the best possible way — I'm over here carefully rationing my 2kW system like it's wartime and this person's running what sounds like a small industrial unit 😂

@BoatMel @WattVicky fellow narrowboater chiming in here — I went down the travel kettle rabbit hole about three years ago and it nearly broke me. Tested four of the things. One took so long to boil I'd genuinely forgotten I'd switched it on.

Current solution on my boat: **Technivorm filter coffee machine