Has anyone run a 12v compressor fridge off solar in a panel van conversion — what size setup are you actually using?

Just getting into the wiring stage of my Transit Custom build and trying to size everything up properly. I've gone with a Brass Monkey 40L compressor fridge (draws around 4-5A when running, maybe 30-40% duty cycle depending on ambient temp). Based on my rough calcs that's somewhere between 14-20Ah per day for the fridge alone, which feels manageable, but I want to make sure I'm not massively underselling the real-world drain.

I'm planning on a 200W roof panel feeding into a Victron 75/15 MPPT, going into a 100Ah lithium leisure battery (a Fogstar Drift). In a decent UK summer I'd expect maybe 60-80Ah from that panel on a good day, but I know we can't always count on that. I'm also working from shore power and the alternator when driving, so it won't be solar-only, but I'd like the system to cope on 2-3 cloudy days without needing to run the engine.

Has anyone run a similar setup and found 100Ah enough headroom, or did you end up wishing you'd gone to 200Ah? I keep going back and forth on whether to add a second 100Ah battery now while the build is fresh, rather than retrofitting later. Equally curious whether anyone's found 200W of solar genuinely sufficient for a fridge plus lighting and phone charging through a typical British autumn weekend.

Not a van person myself — I'm more of a "static caravan in a field pretending I'm off-grid" type 😄 — but the maths is pretty similar whatever you're living in.

Your fridge won't be pulling 4-5A constantly, more like 30-50% duty cycle depending how warm it is outside. So realistically

Running a similar setup in my panel van — 200Ah Fogstar lithium, single 200W panel, and a Victron SmartSolar 20A MPPT.

Honestly the fridge consumption surprised me more than anything else. On hot days mine was cycling far more than I expected, pulling closer to the top end of that 4-5A range consistently.

Few questions before you finalise your sizing:

• Are you planning to charge from the alternator as well, or purely solar?
• What's your typical use case — weekend trips or extended periods?
• Do you have any EV charging aspirations down the line? That changes the whole equation considerably.

The reason I ask is that 200Ah felt adequate until I started thinking about running a small inverter charger alongside everything else. Worth building in more headroom than you think you need upfront rather than retrofitting later.

Great timing on this thread @JaneReid68 — I did almost exactly this build in my Transit last year.

I'd nudge your battery capacity up a bit if you can stretch to it. I'm running 200Ah lithium like @NeilEdwards but I've got two 175W panels rather than one, and honestly that second panel makes a massive difference in the shoulder months — October especially. A single panel on a van roof can really struggle with partial shading from roof bars, aerials, whatever you've bolted up there.

The compressor fridge duty cycle is the key variable people underestimate. Mine runs maybe 30-40% in mild weather but on a hot July afternoon parked in direct sun it's working much harder than that. Size for your worst realistic scenario, not your best.

What orientation are you mounting the panels — flat flush or angled at all?

@JaneReid68 the fridge duty cycle is the bit that catches people out. Mine runs maybe 30-40% in cool British weather but shoot me up to 60%+ the moment I'm parked in the sun in France.

I run a Brass Monkey 35L in my motorhome alongside a Victron SmartSolar MPPT and 300Ah of Fogstar Drift lithium — overkill perhaps, but after 30 years of night shifts I've earned my paranoia about running out of cold milk at 3am 😄

One thing nobody mentions: panel angle matters enormously in a van. Flat roof mount on an overcast British November gives you maybe half what the spec sheet promises. I'd factor that into your calculations rather than trusting peak wattage figures.

Also worth fitting a proper battery protect relay — learned that the hard way when I found my starter battery completely flat in a Tesco car park.

@JaneReid68 the Brass Monkey is a thirsty beast in a black metal van parked in a Tesco car park in July — slap a bit of reflective foil on the ceiling above it or your solar panel will be working harder than a HMRC inspector in self-assessment season.