Anyone else using solar to top up their EV on the off-grid? Curious what's actually working

Bit of an odd one for this forum maybe, but I've been experimenting with using my cabin's solar array to charge the car and thought others might be in the same boat. Running a Victron Multiplus-II 48v system with a 15kWh Fogstar Drift battery bank, and on a decent summer's day I can pull enough surplus to give the Leaf a meaningful top-up — we're talking 8–12kWh on a good day after the cabin loads are covered.

The snag is coordination. I've got a basic granny charger plugged in and I'm manually watching the Victron portal to decide when to switch it on — which is obviously daft. What I want is something that throttles the charge rate based on available solar surplus, like a proper solar divert but for AC EV charging rather than a hot water immersion.

I know the Zappi does exactly this and it's the obvious answer, but £700+ feels steep when the cabin isn't a permanent dwelling and the car's only there half the week. Has anyone bodged something cheaper together — maybe with a Shelly or a Node-RED flow talking to the Victron MQTT feed? Or just gone ahead and bought the Zappi and never looked back?

@BirchRunner not odd at all — this is basically my whole setup now. Got the van conversion running 48v Victron kit and I use the same system to trickle charge the EV overnight when solar's been generous during the day.

Key thing I'd flag: watch your MultiPlus-II's AC output limit. I've got mine capped so EV charging doesn't cannibalise the house loads unexpectedly. I use a basic Type 2 EVSE with adjustable amp dial — drop it to 6A when the batteries aren't fully topped off.

The grid assist / ESS mode is where it gets interesting if you've got any grid connection at all. Keeps everything balanced nicely.

What's your battery bank capacity? That's usually the limiting factor more than the solar array itself.

@BirchRunner not odd at all — I've been doing exactly this at the shepherd's hut for about 18 months.

Key thing I found: don't bother without a proper surplus divert setup. I'm running a Victron MPPT feeding a 48V Fogstar DIY bank, with the Multiplus-II handling AC output. The EV only gets charged once the bank hits ~95% SOC via a simple Node-RED automation watching the Cerbo GX.

Without that logic you'll just hammer your battery bank trying to charge a 60kWh car from a modest array.

Realistic expectations matter too — on a decent summer day I might push 4-6kWh surplus into the car. Useful as a top-up, not a primary charging strategy.

Also worth noting: a Type 2 EVSE with adjustable amperage (I use an Easee) lets you throttle right down to match available solar. Game changer.

@LiamFrost70 same setup here, shepherds hut, 48v Victron system. The bit nobody mentions is that EV charging is an utterly brutal load profile compared to everything else on your system.

My Multiplus-II handles it fine on paper but the MPPT controllers are constantly scrambling to keep up unless solar is genuinely cracking. I've set a minimum SOC threshold of 85% before the car charger even gets a look-in — anything below that and you're just robbing your own batteries.

Worth noting: if you're on a basic EVSE rather than something with proper PWM current control, you can't throttle the draw sensibly. Got a Zappi secondhand which at least lets you set a floor. Massive difference.

Battery chemistry matters too — you'll cycle those cells hard. Fogstar cells have held up reasonably well for me over 14 months of this nonsense.

@SolarJunkie you're not wrong about the consumption side — my shepherd's hut array nearly wept when I first plugged the Leaf in without throttling the EVSE down to 6A.

The bit I'd add: grid assist via the Multiplus-II is your friend here. Set ESS to keep battery SOC above ~60% and let it seamlessly pull from shore (or generator) if solar drops off mid-charge. Means you're not gambling on whether that cloud bank is temporary or not.

Also worth knowing — the Zappi in eco+ mode plays surprisingly well with Victron's frequency-shift signalling if you've got a grid-tie element in the mix. Took me three firmware updates and one spectacular sulk to get it stable, but it works.

Don't go straight for 32A charging unless your battery bank is genuinely beefy. Fogstar cells are good but they're not magic.

@BirchRunner the missing piece for me was a decent EVSE controller that can throttle charge rate dynamically based on available solar. Running a Zappi in eco+ mode tied to my Victron system — when the batteries hit float the excess gets pushed to the car rather than wasted.

Only caveat is minimum charge current on most EVs is around 6A (roughly 1.4kW), so below that the Zappi just waits. On overcast days you can end up with the car sat doing nothing for hours.

Worth checking your Multiplus-II export settings too — took me a while to get the grid code configuration right so it didn't just dump everything back rather than prioritising the charge point.

What inverter capacity are you running? That'll dictate whether you can realistically hit useful charge speeds off solar alone.

Chiming in here as I've been running almost exactly this setup for about 18 months at my place in Dorset. @MarineMike is spot on about the EVSE controller — I went with an OpenEVSE unit flashed with custom firmware that reads available watts directly from my Victron CCGX via MQTT. Took a weekend to get sorted but now it genuinely only pulls what the panels are actually generating above my base load. On a decent summer day I'm getting 8-10 miles of range essentially for free. Winter's a different story mind you — don't expect miracles. The key thing @BirchRunner might want to consider is setting a hard minimum threshold so the EVSE cuts out entirely rather than trickling at 6A and confusing the car's BMS. Happy to share my config if useful.

@DorsetCruiser 18 months of data is gold, would love to know your worst-case winter figures.

Running something similar from my motorhome setup occasionally — 400Ah of Fogstar Drift lithium and 800W on the roof. The EV charging experiment lasted about one afternoon before I realised I was essentially just draining my house bank to move electrons into the car.

The dynamic throttling @MarineMike mentioned is genuinely the only sane approach. Without it you're just hoping the sun cooperates, which in the UK is a bold strategy. What EVSE are you actually using to handle that?

@DorsetCruiser those winter figures would be useful to see — I've been wrestling with the same question at the shepherd's hut.

My van conversion taught me that EV charging is a completely different beast to just running 12v loads. The draw is so unforgiving if your SOC isn't where you think it is.

Currently using a Fogstar Drift 48v battery bank and the Victron MPPT plays nicely with it, but I'm still cautious about committing surplus to the car rather than keeping the hut buffer healthy. How aggressive are you being with your export threshold settings?