Anyone else running an EV charger off solar in a garden cabin? What's your setup?

Just finished wiring up my little off-grid cabin and I'm now wondering if it's realistic to add a slow EV charge from the same system. Currently running a Victron SmartSolar MPPT 100/50 with 400W of panels and a Fogstar 200Ah LiFePO4 battery. Handles lighting, a small fridge, and laptop work fine, but obviously an EV charger is a completely different beast.

I know a proper 7kW home charger is a non-starter without grid, but I've seen people mention using a basic Mode 2 granny cable and throttling it right down to maybe 6A (1.4kW). In theory my inverter could handle the surge, but I'm mainly worried about the solar generation not keeping pace — especially through a UK winter when I'm lucky to get 2–3 hours of usable sun some days.

Has anyone actually done this and tracked the numbers? Curious whether it's worth expanding the panel array first, or if I'd just be hammering the batteries every day and killing the cycle life quicker than it's worth.

@OffGridFreak interesting idea but I'd pump the brakes a bit here. Even a "slow" 3.7kW charge is going to absolutely hammer a 400W array — you'd be pulling from your battery bank far faster than you're putting in, especially on a gloomy UK day (which is... most of them).

In my shepherd's hut I run a similar Victron MPPT setup and I've learned the hard way that EV charging really needs its own dedicated circuit/supply if you want anything sensible.

What might actually work:

• Trickle charging only (6A/1.4kW) overnight if your battery bank is substantial
• Setting a charge schedule via Victron's VRM so it only draws when SOC is above 90%

What's your battery capacity? That's the critical number here.

Rodney58 | 847 posts | ⚡ Solar Enthusiast

@OffGridFreak the maths here is going to be your enemy, I'm afraid. A 100/50 MPPT with 400W of panels is already a modest system, and even a Mode 2 charge via a granny lead is pulling around 2.3kW. That's nearly six times your entire array output.

Unless you've got substantial battery storage and you're only plugging in on a cracking summer afternoon when the bank is already full, you'll hammer your batteries within the hour.

What I'd suggest exploring is a proper solar divert controller approach — only charging when there's genuine surplus available, similar to how people use immersion diverters for hot water. Myenergi do some clever kit in that space.

What's your battery bank capacity? That detail changes everything when we're talking about EV charging viability.

Gemma1981 | 312 posts | ☀️ Off-Grid Convert

@OffGridFreak I'd look seriously at a Zappi charger if you go down this route — it has an "Eco" mode specifically designed to only draw surplus solar generation rather than pulling from batteries. That's your saving grace here, otherwise you'll drain your bank overnight trying to top up the car.

Also worth considering: even trickle charging at 1.4kW is going to need a fairly sustained period of genuine surplus. What's your battery capacity and what's your typical daily load looking like outside of the car? Those numbers will tell you pretty quickly whether this is viable or just wishful thinking during a decent British summer! 😄

ShaunHamilton | 1,204 posts | 🔋 Off-Grid Obsessive

@OffGridFreak the bit nobody's mentioned yet — your battery bank size is arguably more critical than the panel wattage here. Even if you've got decent solar yield, trying to push meaningful charge into an EV overnight or on a cloudy day will flatten most cabin-sized banks embarrassingly quickly.

Worth looking at whether your Victron setup could talk to a solar divert controller so charging only kicks in once your batteries hit, say, 95% SoC. That way the cabin loads are always protected first. The Victron ecosystem handles this sort of logic quite elegantly with some VE.Bus or Node-RED tinkering.

What's your actual battery capacity and chemistry? Lithium vs AGM changes the picture considerably in terms of usable depth of discharge for something this hungry.

BodgeItAndScarper | 2,156 posts | 🔧 Bodging Since Forever

Done something similar on my motorhome setup — trickle charging an EV from solar is possible but you'll be at the mercy of British weather for most of the year, which frankly makes the whole thing marginal at best.

One thing nobody's flagged yet — grid-tie rules aside, if you're genuinely off-grid you'll want to look at minimum state of charge limits on the Victron. Running that battery flat trying to push amps into a car overnight is a good way to kill cells prematurely.

Also worth considering: 400W of panels charging an EV is essentially topping up your anxiety rather than your battery. It'll do something on a decent July day. October through February? Don't bother expecting much.

PikeTom | 63 posts | 🏕️ Hut & Van Tinkerer

Running something similar in my shepherd's hut — same MPPT controller actually. One thing I've been wondering about in your situation: what's your inverter rated at? Even a "slow" 3.6kW Mode 2 charge is going to absolutely hammer an inverter that's sized for cabin loads. I nearly caught myself out with exactly this assumption on the motorhome.

Have you looked at whether a Zappi in eco+ mode could throttle right down to match genuine solar surplus? In theory it can go as low as 1.4kW on single phase, which might actually be workable on a decent summer day with @OffGridFreak's 400W array... though I'd want considerably more panels before attempting it regularly.

What battery capacity are you sitting on?