Can solar + battery realistically handle EV charging in a UK garden office setup?

I've got a 4kWp array on the garden office roof feeding a Victron Multiplus-II 48V system with about 15kWh of Fogstar Drift LiFePO4 cells. Works brilliantly for the office loads — monitors, standing desk, lighting, the lot. But I've been wondering whether I could also use it to do a slow overnight charge on my EV (Nissan Leaf, 40kWh battery).

The maths feels sketchy to me. Even a 7kW wallbox would drain my 15kWh bank in a couple of hours, and that's before considering the office needing juice the next morning. I've been thinking about limiting charge rate to something like 6A via a granny charger — maybe 1.3–1.4kW — so it's not hammering the batteries overnight. But in winter the array barely generates anything, so I'd essentially be burning stored solar and hoping for the best.

Has anyone actually done this in a real UK setup? Wondering if it only makes sense as a summer top-up rather than a primary charging solution. Also curious whether there's a smart way to do it with Victron's ESS or Node-RED to prioritise the EV only when battery SOC is above, say, 80%.

SolarMike | Senior Member

@KenCross great setup! The honest answer is: yes, but with caveats. Your 4kWp will rarely hit peak output here in the UK, so realistically you're looking at seasonal variance being the killer. Summer? Absolutely fine — you could comfortably add slow EV charging (6A on a granny cable draws ~1.4kW) without hammering the Fogstar. Winter though, your 15kWh might barely cover office loads on grey days, let alone topping up a car.

My suggestion would be to use the Victron ESS settings to only permit EV charging when SOC is above, say, 80%. Keeps the batteries happy and ensures you're genuinely running on solar surplus rather than depleting storage you'll need overnight.

What EV have you got and roughly what daily mileage? That'll massively change the answer.

PanelChris | Member

@KenCross Nice system! One thing worth adding to what @SolarMike's touched on — have a look at the Victron scheduled charging feature alongside an Ohme or Zappi charger. You can set the EV to only pull from batteries when they're above, say, 80% SoC, protecting your overnight reserves for the office loads.

Realistically in summer you'll have surplus to play with, but winter's a different story — a 4kWp array in December might only give you 8-12kWh on a decent day across the whole UK, so you'd be barely covering office loads let alone topping up a car.

Worth considering a grid connection as backup purely for EV charging, even if you keep the office fully off-grid. Belt and braces approach. What EV are you running?

Dizzy83 | Member

@KenCross Something nobody's mentioned yet — check your Multiplus-II's input current limit settings before you start pushing EV charging through it. Even if the solar's generating well, the inverter will need to handle the combined office loads plus charger draw, and depending on which Multiplus-II model you've got (3kVA or 5kVA?) you could hit its limits on a cloudy day when grid assist kicks in. Also worth looking at the Victron EVCS or setting up Node-RED to throttle charging based on SOC — keeps you from hammering the batteries during a run of grey days. November through February in the UK can be brutal for that 15kWh recovering overnight. Smart scheduling genuinely makes the difference here.

VoltAlison | Senior Member

@KenCross The part nobody wants to admit: your EV will absolutely drain 15kWh of carefully harvested British sunshine in about the time it takes to brew a decent cup of tea. ☕

That said — I run a similar Victron setup on my static caravan and motorhome charging

DaleSeeker | Member

@KenCross Worth thinking about when you charge rather than just whether you can. I run a similar Victron setup and scheduling the EV to charge during peak solar hours (roughly 10am–3pm in summer) makes a massive difference — you're pulling directly from the panels rather than cycling the batteries unnecessarily. The Multiplus-II paired with a GX device lets you set up ESS rules to prioritise the EV only above a certain battery state of charge, so you're not accidentally draining overnight reserves.

Realistically in UK winters though, expect the solar to barely dent your EV demand on grey days — you'll want a grid connection as backup unless you're comfortable with range anxiety. What's your typical daily EV mileage? That'll determine whether this is genuinely viable year-round.

LazyRanger | Member

My van conversion taught me this the hard way — a 4kWp array on a good July day might scrape 20kWh, but February through March you're lucky to see 6kWh total, and that's before your EV decides it wants a snack.

The maths only works if you treat the car as a dump load for surplus, not a guaranteed daily charge. I'd throw a Victron ESS assistant rule at it — set a minimum battery SOC threshold before EV charging even kicks in, otherwise you'll be hammering those Fogstar cells into the floor every overcast week.

15kWh sounds generous until a Nissan Leaf laughs at it from across the driveway.

NeilSmith | Member

@KenCross One thing worth adding to what @DaleSeeker said about timing — have a look at your Victron's scheduled charging feature alongside a Zappi or similar EVSE that can throttle down to 6A (1.4kW). That way you're not hammering the batteries all at once but trickling charge through the day as solar generation allows. I do something similar and it makes a surprising difference. Also worth checking your Multiplus-II's AC output current limits — you don't want the inverter struggling whilst simultaneously running office loads.

PeakCamper | Member

@KenCross 15kWh sounds generous until you remember your EV laughs at 15kWh for breakfast. 🚗💨

Genuine question though — what are you actually driving? Because there's a massive difference between topping up a Renault Zoe

ExChippie | Member

@KenCross Done something similar — motorhome on a Victron setup, garden office on a separate system. Honest answer: slow charging only, and only when the battery's genuinely topped off mid-afternoon.

The bit nobody mentions — your Multiplus-II has an input current limit. If you're pulling 3.6kW for a Type 2 slow charge and running office kit, you'll hit it fast and the inverter will start load-shedding.

Look at a smart EVSE that reads your Victron's excess solar via MQTT or Modbus and throttles charge rate accordingly. Indra or Ohme can do this with some fiddling.