Has anyone actually run a 12v compressor fridge full-time on solar in a UK van build?

I'm in the middle of a Sprinter 316 build and trying to nail down whether a 12v compressor fridge is genuinely viable as a permanent solution up here in the UK, or whether I'm kidding myself. I've got a 200Ah lithium leisure battery and I'm planning two 175w panels on the roof, but I'm already worrying about November through February when we're getting six hours of weak daylight at best.

The fridge I'm looking at is a Brass Monkey 50L — draws around 45Ah per day according to the spec sheet, though I've seen people say real-world is more like 35Ah if the ambient temperature isn't scorching. On a grim Scottish winter day I reckon I might only pull 80-100w total from those panels. That's not a lot of headroom once you factor in lighting, phone charging, and running a diesel heater fan.

Has anyone got solid data from actual winter use — particularly further north? Wondering whether I need to bump up to 300Ah of lithium, add a third panel, or just accept that I'll be relying on hookup or a B2B charger from the engine more than I'd like.

Davo2 | 847 posts

@WildWanderer Yes, absolutely viable but the UK weather is your friend here more than you'd think - compressor fridges actually work harder in heat, so our grey summers help efficiency! I ran a Dometic CFX35 full-time in my Transit for two years on 200Ah lithium and 300W of panels.

Winter is honestly the bigger challenge - not the fridge itself, but reduced solar harvest. I'd say size your battery bank generously rather than skimping on panels, because you can always tilt panels seasonally but dead batteries on a February overnight are miserable.

What's your planned battery setup? Lithium vs AGM makes a massive difference to your usable capacity calculation. Also, are you doing mostly static pitches or regularly driving? Alternator charging changes the maths considerably.

TimGreen | 312 posts

@WildWanderer Completely doable - been running a Vitrifrigo C42i in my Transit for two years now. Worth knowing that compressor fridges actually become more efficient in cooler UK ambient temps, so our grey summers work in your favour on that front. The real variable nobody mentions is your battery bank size rather than the solar itself. On a proper overcast January week in Scotland I've seen my 200Ah lithium get genuinely stressed with only 200W of panels. I'd say minimum 300Ah and 300W of solar if you're planning full-time winter use. Also mount your panels flush or tilted? Tilt brackets make a noticeable difference at our lower sun angles. What battery chemistry are you going with?

Moorey44 | 134 posts

Running a Waeco CFX35 in my motorhome and yes it's genuinely viable, but I'd stress the battery bank size matters more than the solar in UK conditions. You'll have runs of 3-4 grey days where panels produce almost nothing.

What's your planned battery setup? I've got 200Ah of Fogstar Drift lithium and 200W of panels — fridge draws maybe 30-40Ah per day depending on ambient temp and how stuffed it is.

The thing nobody mentions is that compressor fridges are far more efficient when not running in direct sunlight inside the van. Insulating around it makes a noticeable difference to consumption.

What size fridge are you looking at? That'll change the numbers significantly — there's a big difference between a 40L and an 80L unit in terms of daily draw.

HighlandExplorer | 1,203 posts

Worth adding something nobody's touched on yet — ambient temperature variance across seasons dramatically affects duty cycle. My shepherd's hut setup runs a Brass Monkey 45L, and I've logged Victron Cerbo data showing it barely fires in winter versus near-constant cycling in a July heatwave.

For a van specifically, cab solar gain is brutal. Even on a cloudy Scottish summer day the internal air temp can hit 35°C+ when parked. Factor that into your fridge positioning — insulate behind it from the cab wall if possible.

On the battery side, @Moorey44 is right about capacity mattering, but chemistry matters more. A Fogstar Drift 100Ah LiFePO4 will outperform 200Ah of AGM for fridge duty because you're actually utilising the full capacity without damaging the cells.

What panel arrangement are you working with? That's usually the actual limiting factor up here, not the fridge itself.

XHF_Builds | 847 posts

Great thread. One thing I'd add that nobody's mentioned yet — fridge placement within the van makes a surprisingly big difference. Keep it away from the bulkhead behind the cab (gets roasting in summer sun) and ensure there's decent airflow around the condenser. I've seen builds where people lose 15-20% efficiency just from poor positioning.

Also worth considering a quality PWM or MPPT controller if you haven't already — I swapped from a cheap PWM to a Victron MPPT 75/15 and saw a noticeable improvement in how consistently the fridge stayed powered during marginal days.

@HighlandExplorer raises a fair point about regional variance too — if you're doing proper Scottish highlands trips, budget for more panel capacity than you think you need. Murphy's Law guarantees you'll be parked in a glen with trees on three sides. 🙂