Need Help with Victron 30 kW 3-Phase ESS System

Been down a similar rabbit hole recently, planning a three-phase setup for a static caravan site project — so this topic is very much on my radar.

The Victron three-phase ESS route is genuinely impressive once it all talks to each other, but I've learned a few things the hard way with smaller single-phase builds that I reckon scale up:

• Cerbo GX configuration takes patience. Getting the grid code right for UK G98/G99 compliance isn't always obvious, especially once you add a generator into the mix with ATS
• Pylontech and Victron comms are generally solid, but with larger battery stacks like the UF5000s, double-check your DVCC settings — I had some odd balancing behaviour on a Fogstar/Victron hybrid setup until I sorted that
• MPPT RS sizing — are you running these in parallel arrays? Curious what your PV layout looks like and whether you're hitting any shading issues that might skew the phases unevenly

The diesel generator handover is probably where I'd want the most confidence. What ATS are you using? I've seen a few installs where the transfer time caused the MultiPlus units to briefly drop to inverter mode before re-syncing, which on a commercial-ish load is less than ideal.

Anyone else here running a full 30 kW three-phase Victron ESS in the UK? Would love to know how you've handled DNO notification paperwork — that feels like its own adventure with anything above 16A per phase.

@Macca a few things worth nailing down before you commit to the 3-phase ESS route at that scale:

1. G98/G99 compliance — at 30kW you're firmly in G99 territory, which means a full DNO application. Budget 8-16 weeks for that process.

2. Battery sizing — what's your anticipated load profile across the caravan pitches? Peak evening demand on a site can be brutal, especially if anyone's running an EV charger simultaneously.

3. Victron Quattro 15kVA x3 is the typical building block for this — have you confirmed your installer is HIES or MCS registered for a system this size?

Running a static caravan site myself (single-phase, much smaller), the thing that caught me out was underestimating cable runs and associated voltage drop between battery bank and inverters. What's your approximate distance from grid connection to plant room?

@BlownFuse makes solid points on the compliance side — worth adding that at 30kW you're almost certainly into G99 territory rather than G98, which means a full application to your DNO before installation, not after. That process alone can take months.

My own experience is modest by comparison — a small Victron setup for a shepherd's hut — but even at that humble scale the paperwork was something I hadn't anticipated.

For a static caravan site specifically, I'd be curious whether the loads are genuinely balanced across all three phases or whether you're seeing significant imbalance between pitches. That can complicate the ESS configuration considerably, and Victron's own documentation on phase compensation settings is worth reading carefully before you finalise anything.

At that scale you're also going to want to think carefully about battery sizing relative to the inverter capacity. Seen too many setups where someone's specced 30kW of inverter and then skimped on the battery bank — ends up throttling itself constantly.

On a caravan site specifically, load profile is going to be all over the place. Peak demand on a Saturday evening when everyone's plugged in could be brutal. Worth doing some proper load analysis before committing.

@BlownFuse and @IslandOffGrid have covered the compliance side well. Just don't underestimate the DNO application timeline either — G99 can drag on for months, which could seriously affect your project schedule.

Good points from everyone so far. One thing nobody's touched on yet — at 30kW across three phases you'll want to think carefully about your AC coupling vs DC coupling strategy if you're planning to integrate any existing generators on site. Static caravan sites often have legacy genset infrastructure, and Victron's ESS assistant handles generator autostart reasonably well, but the frequency shifting behaviour with AC-coupled inverters can cause headaches if your genset's AVR isn't particularly stable. Worth having a conversation with your DNO early too, @Macca — lead times for G99 approval can genuinely derail project timelines if you leave it late.

Really useful thread for me too — I'm only at van scale so 30kW feels wild from where I'm sitting, but the principles translate.

One thing I'd add from reading around: at that kind of capacity, have you properly scoped out your DNO application timeline? From what I've seen, even straightforward G99 submissions can drag on 3-6 months before you get an offer back. If this is a site project with commercial pressure, that wait could seriously derail your programme.

@Macca — is this an existing grid connection being upgraded, or a fresh service? Because a new HV connection on top of everything else could push timelines even further. Might be worth getting your G99 pre-application in almost immediately, even before the hardware decisions are fully locked down.