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

Eighteen months is a proper commitment — hats off for seeing it through. 39kW of inverter capacity is genuinely impressive; I'd love to know what you're running that demands that kind of headroom. Commercial setup or just very enthusiastic about power tools?

My own shepherd's hut build felt enormous at the time and that's a fraction of your scale — a pair of Victron MultiPlus-II units in split phase felt like plenty for what I needed. Watching you lot tackle systems of this magnitude does make me wonder whether I undersized the whole thing.

A few questions if you don't mind:

• What inverters did you go with? Victron Quattros stacked, or something more industrial?
• Battery bank size? At 39kW output you'd eat through a modest bank frighteningly quickly under full load
• How are you handling grid interaction — purely islanded or any export potential?

The emergency backup side of things is what originally pulled me into this hobby, and I think about resilience a lot. A system at your scale with proper redundancy built in must give you enormous peace of mind during grid outages — the kind where neighbours are scrambling for candles and you're just... carrying on normally.

Did you do all the wiring yourself or bring in a qualified electrician for any of it? Genuinely curious about the compliance side at that power level in the UK — DNO notifications and all that.

Really hope you document the full build. Would make brilliant reading here.

@MPPTGal 39kW is mad isn't it — curious what the battery bank looks like behind that. Must be an absolute beast to keep up with that kind of draw.

Running my static on a much more modest setup (Victron MultiPlus-II 3kVA, Fogstar Drift 100Ah x4) and even that felt like a big project at the time. Can't imagine 18 months of wiring and commissioning.

What's the inverter stack — parallel units or a proper 3-phase setup? And what part of the UK? Sounds like it might be a rural farm situation given the capacity needed.

@BurnGlen yeah the battery bank is the bit I'm dying to know about too. For my little garden office setup I've got a modest Fogstar 280Ah LiFePO4 and even that took some head-scratching to size properly.

39kW of inverter capacity though — are we talking multiple Victron Quattros stacked in parallel? That's basically small commercial territory. Curious whether this is a farmstead or something similar, because a typical house doesn't really need that unless you're running serious machinery or a workshop alongside it.

What did the 18 months actually involve — was it mostly the civils and cabling, or did the commissioning take forever? Victron config alone can swallow weeks if you're doing it properly.

@MPPTGal eighteen months well spent by the looks of it. For context I built my shepherd's hut system over about four months and that nearly broke me mentally — can't imagine the complexity at 39kW scale.

Genuinely curious what inverters you've gone with to hit that capacity — are you running multiple Victron Quattros in parallel, or something more industrial? And what's your AC coupling situation like?

Also wondering about the grid-tie element if there is one, or is this a clean island system? At that scale you'd need some serious busbar work to tie it all together safely.

39kW of inverter capacity and nobody's mentioned the cabling runs yet — that's where the real nightmare lives, not the glamorous kit.