Has anyone run a 12v fridge off solar on a narrowboat through a UK winter?

Thinking of keeping my narrowboat on the cut through winter this year rather than laying her up, and I'm trying to work out if my current solar setup is actually going to cut it for keeping a 12v compressor fridge running. Right now I've got two 175w panels on the roof feeding into a 100ah lithium battery via a Victron SmartSolar 100/30 MPPT. Works brilliantly from April through to October but I've never tested it properly in December or January.

The fridge is a Dometic CFX3 35, which draws around 45w when the compressor kicks in and averages maybe 20-25ah per day in mild weather. My concern is that in a proper grey UK winter, especially moored up under trees or in a cutting, I might only be getting an hour or two of usable solar gain per day — if that. The lithium is obviously better than AGM for depth of discharge but 100ah still feels marginal over a run of overcast days.

Has anyone actually done this and got real-world data from their setup? I'm wondering whether it's worth adding a third panel or bumping the battery bank to 200ah before the cold weather hits. Also curious whether anyone's integrated a Sterling B2B charger to top up off the engine alternator on days when they're not getting any solar at all — seems like the sensible belt-and-braces approach but I'd rather hear from people who've done it than just go off YouTube videos.

PYW_VanLife | 847 posts

@OllieGraham91 Done exactly this in a van context so the solar side is pretty transferable. Honest answer: December and January will humble you. I'm in the Midlands and some days you're getting maybe 1-2 usable hours of decent solar. The fridge will likely pull 30-50Ah daily depending on ambient temps (ironically cheaper to run in winter as it doesn't have to work as hard).

My genuine advice - what's your battery bank capacity? That matters more than panel wattage over winter. I run 200Ah lithium and it's tight some weeks even with the van's alternator topping up whilst driving.

A narrowboat has the advantage of engine hours for alternator charging though, so if you're doing decent cruising or running the engine daily you'll be far better placed than I am. What size panels have you got currently?

RobWebb59 | 1,243 posts

@OllieGraham91 Narrowboat specific here - done three winters liveaboard on the cut. Honest answer is that solar alone through December and January is going to struggle. You're looking at maybe 2-3 usable hours of decent generation on a grey day, which simply isn't enough to run a fridge continuously. Most boaters I know run their engine for an hour or two daily anyway for heating, and that alternator charging makes all the difference. A decent 100Ah leisure battery bank combined with engine charging keeps the fridge ticking over fine. I've got 200W of panels on my roof and they're largely decorative November through February if I'm honest! What's your current battery capacity? That's probably the more important question than the panels themselves for winter liveaboard.

WattCharlie | 312 posts

@OllieGraham91 Worth knowing that December/January in the UK you're realistically looking at maybe 1–2 usable sun hours on a good day, and that's if you're not moored up under tree cover or facing the wrong way.

For a 12v fridge specifically — a decent compressor unit like a Dometic or Engel will pull maybe 30–40Ah/day in cold ambient temps (actually works in your favour vs summer).

The real question is your battery capacity. What are you running? If it's anything less than 200Ah of usable lithium, you'll be leaning heavily on engine alternator time to top up regardless of panels.

On my shepherd's hut I've got 400W of Renogy panels and even that struggles mid-winter — a boat's roof mounting angle makes things trickier still.

VitoDream | 578 posts

@OllieGraham91 One thing nobody's mentioned yet - canal orientation really matters on a narrowboat. Unlike a van or static install, you're constantly mooring at different angles, so your panels might face completely away from the sun for days at a time. I'd factor in at least a 50% efficiency reduction beyond the usual winter calculations just for that alone. A tiltable panel mount helped me enormously when I had the boat. Also worth considering that locks and tunnels can shade you unexpectedly mid-day when you're actually moving. What's your current battery bank capacity? That's arguably more important than panel wattage through the darker months - you want enough storage to carry you through two or three grim days without needing the engine running constantly.

ExFarmer | 847 posts

Run a Fogstar-backed 200Ah LiFePO4 bank with a pair of 175W panels on the roof — fridge hasn't missed a beat, but the engine does the real heavy lifting November through February if I'm honest.

ThistleRunner | 203 posts

Great thread this. One thing I'd add to what @ExFarmer and @VitoDream have touched on — don't underestimate how much your engine hours will carry you through the dark months. Even a couple of hours cruising every few days makes a massive difference to your battery state of charge when the panels are barely producing. If you're moored up static all week though, that's where it gets dicey. I'd also look hard at your fridge's ambient temperature setting if it has one — running it in a cold boat means the thermostat cycles far less frequently, so your actual consumption drops noticeably compared to summer. What panels and battery capacity are you currently working with @OllieGraham91? That'd help give you a more honest answer about whether you need to add anything before the clocks go back.

Roger1983 | 1,247 posts

Worth mentioning engine run time as part of your overall strategy too. On my boat I've got a 100A alternator with a split charge relay, and even a 45-minute cruise every couple of days makes a significant difference to the battery state during those grim January stretches when the panels are basically decorative. @OllieGraham91 what's your current battery bank capacity? That's arguably more critical than panel wattage for winter liveaboard use — you need enough storage to ride out three or four consecutive overcast days without the fridge cycling down.

IslandExplorer | 312 posts

The angle thing is the killer in winter — December sun barely clears the canal-side trees on a lot of moorings. I built a simple tiltable frame for my panels on the garden office setup and gained a noticeable chunk of output just by going steeper. Narrowboat roofs are trickier but not impossible with the right brackets. Also worth checking your fridge's actual draw with a Victron BMV — most people massively overestimate consumption until they measure it. The Compressor fridges (Waeco/Dometic) are genuinely miserly compared to thermoelectric ones.