Sizing a hybrid inverter for a garden office + overnight EV charging — where's the sweet spot?

Been running my garden office on a Victron MultiPlus-II 3kVA / 48V for about 18 months now, paired with 8 × Fogstar Drift 100Ah cells in a DIY 48V pack (roughly 19.2kWh usable). Solar input is 2.4kW across 8 panels on a south-facing lean-to roof, all going through a SmartSolar MPPT 150/60. Works brilliantly for the office loads — standing desk, monitors, a small NAS, the usual.

The problem is I've recently picked up a second-hand Nissan Leaf (24kWh battery, usually arriving home at around 40% SOC) and I'd like to push overnight charging through the same system rather than run a separate grid-tied circuit. Even a modest 3.7kW Type 2 charge would completely swamp the MultiPlus at its current rating, especially if the pack has been drawn down during the day. I'm wondering whether jumping to the MultiPlus-II 5kVA makes practical sense, or whether I'm better off looking at a parallel setup.

The tricky bit is grid interaction — I'm on the edge of a rural village, so grid supply here is genuinely weak (voltage regularly hits 253V and the DNO has been... unhelpful). The appeal of the hybrid setup is that the battery absorbs the overnight Leaf charging load and I top it back up with solar the next day, keeping peak grid draw low. My back-of-envelope maths suggests that on an average day with ~15kWh of solar yield (summer obviously), I could recover most of what the Leaf takes without touching the grid at all.

Has anyone actually done this — used a Victron-based off-grid or hybrid system as the primary charging source for an EV? Curious what inverter sizing you landed on, whether you had any issues with the Leaf's onboard charger behaving oddly with inverter-sourced AC, and whether the Venus OS power

ValleyAmy | 312 posts | Shropshire

@RoundTuit that's a solid setup already! One thing worth considering before jumping to a bigger inverter — have you looked at time-shifting the EV charging rather than running it simultaneously with office loads? Even a basic scheduled charge via your car's onboard timer could let you keep the MultiPlus-II 3kVA and just accept slower overnight charging.

That said, if you genuinely want both running concurrently, the 5kVA MultiPlus-II is the obvious next step and keeps you in the Victron ecosystem without relearning everything. The jump from 3kVA to 5kVA isn't massive cost-wise but the peace of mind is worth it in my experience.

What's your actual peak office draw looking like? That'd help nail down whether the sweet spot is the 5kVA or if you're fine managing loads cleverly.

ShaunHamilton | 312 posts

@RoundTuit solid setup to start with, but overnight EV charging is a different beast entirely. Even a modest 7kW home charger will absolutely flatten that pack before dawn unless you're throttling it right back.

Worth looking at whether your DNO will allow a separate grid connection to the office plot — some won't without significant faff. If you're staying islanded, I'd honestly consider bumping to a MultiPlus-II 5kVA minimum and doubling your battery capacity before touching the EV charging side.

Also worth factoring in winter solar yield — 2.4kW array in December is doing very little overnight obviously, but daytime harvest will be poor too. What's your grid tie situation currently? That changes the conversation significantly.

WattEd | 847 posts | Array

The MultiPlus-II 3kVA is your bottleneck here — 2.4kW continuous AC output won't shift meaningful range overnight. Even a Mode 2 "granny charger" wants 2.3kW sustained, leaving almost nothing for the office loads.

Worth crunching the actual kWh deficit rather than peak draw. If your EV needs 15kWh overnight and your 19.2kWh pack is already depleted by evening office use, you're asking the inverter to both charge the EV and sustain itself — that maths goes wrong quickly.

For my shepherd's hut setup I'd seriously look at the MultiPlus-II 5kVA before anything else. Same 48V architecture, slots straight into Cerbo GX/VenusOS without headaches, and the extra headroom lets you implement proper ESS charge scheduling via Node-RED to hit off-peak rates if you're grid-tied.

What's your actual evening SOC typically sitting at before you plug the car

MidlandsSolar | 203 posts | Array

@WattEd is right about the 3kVA being the ceiling, but worth flagging — even if you upsize to a 5kVA MultiPlus-II, your battery pack is the real constraint for overnight EV charging. Pulling 3.5kW+ for 4-6 hours will hammer a 19.2kWh pack pretty hard before solar kicks back in at dawn.

Running a similar setup on my garden office here. What I'd genuinely consider is keeping the office load separate from EV charging and setting a scheduled charge window in VictronConnect — only charge the EV once SOC hits, say, 80%+ from daytime solar. Avoids the morning scramble entirely.

What's your typical EV charge requirement overnight — full top-up or just a top-off?

DODNerd | 1,204 posts | Array

Something nobody's mentioned yet — have you looked at the MultiPlus-II 5kVA as a drop-in upgrade? Same 48V bus, same VE.Bus comms, so your existing GX device and battery config carry straight over. You'd jump to ~4.5kW continuous which opens up a proper Mode 2 charge at 10A (2.3kW) overnight without sweating the inverter.

The real question is your battery — 19.2kWh sounds generous until you factor a meaningful EV top-up plus overnight loads. What's your typical morning SOC before solar kicks in? If you're regularly waking up below 30% you'll want to model that before throwing money at a bigger inverter. DVCC settings in Cerbo will let you stagger the EV charge to protect the pack too. Worth a look before upgrading anything. 🔋

DownsCruiser | 1,204 posts | Array

Done exactly this in my motorhome-turned-cabin setup. The bit nobody mentions: AC coupling lag. When the EV charger kicks in overnight it can pull hard before the inverter's frequency shift kicks in — I've had the MultiPlus trip on me twice doing something similar.

If you're dead set on keeping the 3kVA, wire the EV charger on grid-passthrough only and set an overnight grid charge window via VRM. Means you're not asking the inverter to do the heavy lifting at all.

Otherwise honestly just jump to the MultiPlus-II 5kVA. Second-hand ones pop up on eBay regularly around £600-700. Your 48V bank is already right for it, so it's a straight swap.