Charging an EV from a cabin solar setup — anyone actually doing it regularly?

Been toying with the idea of running a basic slow charge (3.7kW) for my van from the cabin array when I'm parked up. Got a 4kW roof setup feeding a Victron Multiplus-II 48/5000, so theoretically it's there on a decent day.

Problem is the cabin load itself — fridge, lights, occasional power tools — chews through more than I expected. Realistically I reckon I've got maybe 1.5–2kW spare on a good sunny afternoon before the batteries start drooping below 80% SOC.

Thinking about setting an ESS rule to only allow EV charging when SOC is above 90% and solar input is above 2kW. Anyone done something similar in VictronConnect or Node-RED? Wondering if it's actually worth the faff or if I'm better off just running a dedicated smaller array straight to a Type 2 EVSE.

@PV_Fan tried something similar at my place last summer. Theoretically fine, practically a nightmare unless you've got really consistent sun.

Problem is your Multiplus-II is inverting to run that charger, so you're losing efficiency both ways. Also 4kW array rarely delivers 4kW — factor in clouds, angle, temperature derating and you're often looking at 2.5kW actual output.

What I found works better:

• Charge mid-morning to early afternoon only
• Watch your battery SOC like a hawk
• Set a hard cutoff so you're not draining your cabin bank

What's your battery capacity? That's the real bottleneck. If you're on a smallish 10-15kWh pack you'll barely get meaningful EV range before you've hammered your storage.

Doable for a top-up, not as a primary charging strategy.

@PV_Fan funny you mention this — I've been doing exactly that with the boat setup for a couple of seasons now, and it's less plug in and forget and more check the weather forecast, sacrifice a biscuit to the solar gods, and hope for the best.

The bit nobody warns you about is that a 3.7kW draw is almost your entire array on a good day. One cloud rolling over and your Multiplus is pulling from the battery bank rather than the panels. Works brilliantly June through August; October onwards it's basically just slowly annoying your batteries.

My workaround — set the charge current right down to around 6A via the EVSE settings. Daft slow, yes, but it plays much nicer with variable generation and your bank doesn't take a hammering. Overnight gains are modest but it adds up across a weekend parked up.

@PV_Fan I've been doing something very similar down here in Cornwall for about 18 months now. The key thing nobody mentions is state of charge management — I use a Cerbo GX to set a minimum SOC threshold before the Multiplus will even consider diverting to the van. Set mine at 60%, which gives the cabin comfortable overnight autonomy before charging kicks in.

The other gotcha is morning cloud cover mid-charge — your Multiplus will throttle back and the van's onboard charger can get a bit unhappy with fluctuating input. Worth enabling the ESS assistant if you haven't already.

What battery bank are you running? That'll make a big difference to whether 3.7kW draw is sensible or whether you'd be better dropping to 1.8kW and being more patient about it.

Great thread — @CornishWanderer is right that there's usually something crucial people gloss over, and I'd add: watch your battery state of charge before you even think about plugging in. I made the mistake of starting a charge session with my bank already at 60% from overnight loads, then cloud rolled in around 11am and my Multiplus started pulling from batteries to compensate. Ended up draining them further than I'd have liked by mid-afternoon.

What's worked for me is setting a hard SOC floor in VictronConnect — I won't allow EV charging unless batteries are sitting above 85%. Means some days the van simply doesn't get topped up, but that's the reality of living within your means off-grid, isn't it. Also worth checking your cable ratings if you're running 3.7kW for extended periods. Mine got uncomfortably warm before I upgraded.

Really interesting thread! @Kingy I'd love to hear more about the boat setup experience.

One thing worth flagging that nobody's touched on yet — watch your battery state of charge before you start a session. I made the mistake of plugging in on a cloudy morning when my bank was already sitting at around 40%, thinking generation would keep pace. The Multiplus pulled from batteries to compensate and I ended up in a right mess by early afternoon.

I now have a simple rule: won't start charging the van unless batteries are above 85% AND the forecast looks reasonable. Sounds obvious but it's easy to be optimistic when you're keen to top up the van!

Also worth checking your DC cabling runs to the Multiplus are properly rated — sustained 3.7kW draws do funny things to undersized connections over time.

Really interesting thread — I've been doing this at my Highland setup for two seasons now and the thing that catches most people out is the battery state of charge timing. I make sure the bank is sitting above 80% before I even think about initiating a charge session, otherwise the Multiplus starts clipping and the van's onboard charger gets confused by the fluctuating input.

Also worth mentioning — @PV_Fan your 4kW array sounds sufficient on paper but factor in that Scottish/northern UK summers give you maybe 4-5 peak sun hours on a good day. I tend to do short top-up charges rather than trying to push a significant range back in one sitting. Manages expectations brilliantly and stops you chasing your tail when cloud rolls in. What battery capacity are you working with?