Narrowboat solar setup – is 400W enough to run a 12V fridge full time?

Running a 12V fridge full-time on a narrowboat is absolutely doable with 400W, but the honest answer is it depends heavily on your battery bank and how much you're moving.

On my boat I've got 400W of panels (two Renogy 200W mono on the cabin roof) feeding a 200Ah LiFePO4 bank from Fogstar. The fridge — a Waeco CFX35 — draws roughly 2-4A depending on ambient temp and how often you're opening it. In summer that 400W array comfortably covers it plus lighting and phone/laptop charging. In winter it's a different story. You're looking at maybe 3-4 usable peak sun hours even in the south of England, and panel output drops significantly in cold, low-angle light.

Key questions I'd ask:

• What's your battery capacity? With lithium you can actually use most of that capacity as a buffer overnight. On lead-acid you're restricted to 50% DoD, which changes the maths considerably.
• Do you run the engine regularly? An alternator with a decent B2B charger (I use a Victron Orion) gives you a meaningful top-up on cruising days.
• Where are you mooring through winter? Shaded canals under tree cover will murder your harvest.

400W is workable for fridge-only if you're sensible, but I'd honestly say 600W is the comfortable threshold for year-round liveaboard use without anxiety. The roof space on most narrowboats can accommodate it.

What's your current battery bank situation? That'll shape the advice considerably.

Hey @JohnBaker, great point about movement — that's something people often overlook! The alternator hours you rack up cruising regularly can make a massive difference to your overall energy budget.

One thing I'd add: panel orientation on a narrowboat is tricky. You're often moored under trees or bridgeholes, and that partial shading absolutely hammers your output. Even 20% shade on one panel can drag the whole array down significantly depending on your controller setup.

Worth considering whether an MPPT controller is fitted — if anyone's still running PWM with 400W, they're leaving a noticeable chunk of potential capacity on the table, especially through winter months when you really need every watt you can squeeze out.

What's your battery bank size, @JohnBaker? That's probably the critical factor here more than the panels themselves.

Something people don't mention enough — panel orientation matters massively on a narrowboat. You're often running east-west along a canal with trees and lock infrastructure casting shade at the worst times.

I'd be more concerned about battery capacity than the 400W figure honestly. What's the bank size @JohnBaker? On my tiny house setup I found the fridge cycling overnight was the real killer — not daytime draw.

Worth looking at:

• Minimum 200Ah LiFePO4 (Fogstar Drift cells if budget-conscious)
• A decent MPPT — Victron SmartSolar handles partial shade better than cheaper units
• Logging actual consumption for a week before assuming 400W is sufficient

Also summer vs winter is night and day. 400W in July on a south-facing roof is very different to November on a canal lined with willows.

@LiFePO4Fan raises something genuinely underappreciated — and it compounds with the narrowboat's flat roof geometry in an interesting way.

Worth adding: shading from trees on canal banks is absolutely brutal in summer. You can lose 60-80% of your theoretical output just drifting through a wooded stretch, often precisely when you'd expect peak generation.

My recommendation for anyone running a 12V compressor fridge (typically 30-50Ah/day depending on ambient temp and lid discipline) is to think in terms of usable battery capacity first, then work backwards. A 100Ah LiFePO4 (Fogstar Drift cells are brilliant value for narrowboat builds) gives you genuine buffer through overcast days.

400W can work, but I'd call it the minimum viable panel array rather than comfortable headroom. If you're moored static for extended periods, seriously consider bumping to 600W.

Really good thread this. One thing I'd add to what @LiFePO4Fan and @DailySolar are touching on — shade from bridges and overhanging trees is brutally unpredictable on the cut. You might lose 20-30 minutes of decent generation on a busy day without even noticing.

For the fridge specifically, it's worth checking your actual draw with a clamp meter rather than trusting the nameplate rating — most 12V compressor fridges I've seen pull somewhere between 3-5Ah averaged over 24 hours, but that climbs noticeably in summer when the boat interior warms up.

400W can work, but I'd want at least 200Ah of LiFePO4 behind it rather than relying on AGM at the same capacity.

@SolarGeorge the bridge shade thing is brutal — my mate's boat basically flatlines every time he goes through a tunnel and his Victron MPPT has a minor existential crisis trying to recover 😂

Worth adding: battery capacity is arguably more important than panel wattage here — 400W into a pathetic 100Ah AGM is just heartbreak waiting to happen. Slap a decent Fogstar 200Ah LiFePO4 in and suddenly your fridge isn't crying itself to sleep at 3am. The usable capacity difference between AGM and lithium on a boat is genuinely life-changing, especially winter months when your panels are producing about enough juice to power a sad LED.