Narrowboat solar setup – is 400W enough for a liveaboard?

Lived on a narrowboat for three winters before moving to my current land setup, so this one's close to my heart.

400W can be enough, but it really depends on what you're running and — crucially — where you're mooring. Towpath shade is the silent killer of solar yields. I had 360W on the roof and spent half my time shuffling the boat along just to chase a decent patch of sun in November.

The bigger question is battery capacity. My old setup was two 100Ah AGMs and the panels would fill them by midday on a good summer day, leaving all that afternoon generation wasted. Upgrading to a single 200Ah Fogstar lithium completely changed the game — better depth of discharge, faster acceptance, and I could actually use what the panels produced.

A few things worth thinking through:

• Inverter loads — are you running a washing machine, induction hob, or just 12V appliances?
• Engine hours — most liveaboards cruise regularly, so alternator charging fills the gaps nicely
• Victron MPPT — non-negotiable in my opinion, the difference in harvest over a cheap controller is measurable

400W with a decent lithium bank and a Victron SmartSolar 100/30 is a solid foundation. You might find it stretched thin in December/January though, especially if you're static.

What's your current battery setup looking like, and are you planning to cruise regularly or stay on one mooring?

@SolarJo curious where you cut off there — guessing you were going to say "weather" lol

Anyway — narrowboat winter is brutal for solar. Short days, panels often shaded by bridges/trees along the canal, angle's all wrong. 400W looks great on paper.

My garden office gets similar rated wattage but I'm on land with a proper tilt mount. Boat panels are basically flat so you're losing loads.

Few things I'd add:

• Battery capacity matters more than panel wattage on a boat imo
• Fogstar lithium holds up well in cold bilge temps
• Victron MPPT is non-negotiable, squeeze every watt you can get

Are they running an inverter for anything heavy? That'll kill 400W dead in winter. Diesel heating and gas cooking saves your battery massively on a liveaboard.

@SolarJo 400W on a narrowboat roof is optimistic for winter — you're lucky to squeeze 20% efficiency out of panels sitting flat at 51°N in December, so you're realistically working with 80W-ish on a good day, which won't touch your inverter losses alone.

The real answer is alternator charging whilst cruising doing the heavy lifting, with solar as the top-up. A decent 200Ah LiFePO4 bank (Fogstar Drift is popular for the weight saving in a floating vessel) paired with a Victron SmartSolar MPPT means at least your data is honest about how badly the sun's letting you down.

400W becomes genuinely useful come April. Until then, factor in your engine hours as part of the actual energy system — boats have that luxury, unlike my static setup.

@OldSailor is right but underselling it — flat panels on a narrowboat roof are a nightmare. Zero tilt adjustment, trees on both towpaths, bridges blocking sun half the morning. My shepherd's hut setup at least lets me angle properly.

400W nameplate in December might genuinely give you 40-60Wh on a bad day. That's it. People forget peak sun hours in the UK midwinter are basically a joke — 0.8-1.2 in many areas.

You need to actually calculate your loads rather than just throwing panels at the problem. What's the inverter doing, what's the fridge rated at, are you running a diesel heater with a fan motor?

Also engine alternator hours matter massively on a liveaboard — that changes the whole equation. Without knowing that, nobody can tell you if 400W is enough.

@BatteryTim this is exactly what made me curious about boats vs vans — in my van conversion I can at least angle-park to chase the sun a bit, but a narrowboat is just... stuck wherever the mooring is, right?

Quick question for anyone who's done it: does running a small Victron MPPT with adaptive absorption help claw back anything meaningful on those grim December days, or is the battery bank size the real lever to pull?

I'm also wondering whether a Fogstar lithium bank vs AGM makes a bigger practical difference in winter for a liveaboard — presumably you want every usable amp-hour you can get when the panels are basically decorative from November onwards?