Retrofitting solar on a narrowboat — worth the hassle or just get a genny?

Been mulling this over for a while. My mate's just bought a 57ft narrowboat and he's asking me to help him sort the electrics. I've done my shepherd's hut setup (2x 200W panels, Victron MPPT, 2x Fogstar 100Ah lithiums) so I've got some background, but a boat feels like a different beast entirely — roof space is awkward, panels need to be walkable or at least not a trip hazard, and the mooring situation means shade is unpredictable.

He's looking at roughly 300–400W of flexible panels across the cabin roof, feeding into a Victron SmartSolar 100/30. Battery bank is TBD but probably 200Ah lithium to start. The main loads are a 12V compressor fridge, LED lighting, phone/laptop charging, and occasionally a small inverter for power tools. No central heating pump or anything too heavy.

My concern is whether flexible panels are actually worth it on a boat long-term — I've heard they delaminate faster in the damp and they run hotter than rigid panels which kills output. Has anyone gone down the rigid panel route on a narrowboat roof and actually made it work without it being a complete eyesore or obstacle course?

Also curious what people are doing for alternator charging on the engine — is a Sterling B2B a sensible addition alongside the solar, or overkill for this kind of setup?

@GazPrice done exactly this on my 58-footer last season. Roof geometry is the real challenge — you lose usable area to cratch cover, mushroom vents, and the tiller end. Realistically budget for 300–400W maximum on a standard cruiser stern without getting creative with angled mounts.

Key considerations specific to boats:

• Tilt vs flat-mount: flat keeps centre of gravity low and avoids snagging bridges, but you sacrifice 20–30% yield
• Semi-flexible panels attract canal folk but I'd avoid them long-term — delamination issues within 3 years on mine
• Cable runs are longer than you'd expect once you're routing through the gunwale properly; factor in voltage drop carefully

Pair it with a Victron SmartSolar 100/30 and decent lithium (Fogstar Drift cells are well-suited to marine use) and a genny becomes genuinely occasional rather than daily.

Roof shading from the tiller, chimney, and any roof boxes catches a lot of people out — worth doing a proper template on paper before ordering panels. On a 57-footer you've realistically got maybe 6-8 panels depending on layout, but partial shading from bridges and canal-side trees will hammer your yield more than on a static install. That's why I'd strongly recommend individual MPPTs or at minimum a decent string with shade optimisers rather than wiring everything in series. @DefenderWanderer is right about geometry being tricky. The genny argument falls apart pretty quickly once you factor in diesel costs, noise complaints at moorings, and the hassle of running it in a tunnel. Your shepherd's hut experience with Victron will translate well — just expect more compromises on panel placement than you're used to.

Really interesting thread — my shepherd's hut build taught me that shading calculations on paper are almost always optimistic once you factor in real-world obstructions.

One thing I'd flag for a narrowboat specifically: flex. Narrowboat roofs have more give than you'd expect, especially older steel ones. Rigid aluminium-framed panels can stress and crack if mounted directly onto a flexy roof — semi-flexible panels or proper rubber feet with a bit of float in the mounting can save a lot of heartache.

Also worth thinking about orientation lock-in. On a hut or motorhome you occasionally reposition, but a canal boat sits at whatever angle the mooring dictates. I'd lean toward a slightly oversized array with a Victron MPPT that can handle the variation, rather than trying to optimise tilt.

The genny question answers itself once you've lived with silent solar for a week. No contest.

Dizzy60 | Posts: 847

Good timing on this thread — just finished a very similar job on a friend's 60ft trad stern last autumn.

One thing nobody's mentioned yet: think carefully about panel orientation relative to the towpath side. On some popular canal stretches you'll be moored up for hours with tree canopy on one side consistently, so knowing which way your boat typically sits can actually influence where you prioritise panel placement along the roof.

Also worth factoring in that narrowboat roofs flex more than people expect — use proper marine-grade cable entry glands and don't skimp on the UV-resistant conduit runs. I'd also strongly recommend a Victron setup with Bluetooth monitoring; being able to check state of charge from the cabin without going topside is genuinely useful when it's hammering it down in November.

Generator as backup absolutely makes sense, but solar will cover the majority of your daily needs comfortably through spring to autumn.

Right, narrowboats are a different beast to static builds and I'd caution against just scaling up what works on land.

The critical thing nobody's mentioned yet: orientation changes constantly. Moor facing east on a canal cutting with trees either side and your lovely south-facing calculation is worthless. I've watched narrowboat owners obsess over tilt angles when the canal heading is the actual variable killing their yield.

On a trad stern specifically, you're working with maybe 8-10 usable metres of roof once you account for @EwanGreen's shading points. Realistically that's 600-800W max, and that's before you factor in dirty canal-side trees.

My honest take: both. Small generator for winter and heavy loads, solar handles summer baseload. Trying to eliminate the genny entirely on a liveaboard is setting yourself up for misery come November.

Great timing for me to chip in — I've got both a garden office and a shepherd's hut running off solar so I've been down the shading rabbit hole more than once.

The narrowboat roof is honestly a nightmare compared to my hut. On my shepherd's hut I just tilted the panels south and forgot about it. On a boat you've got bridges, trees, locks — constant partial shading.

Strongly recommend Victron SmartSolar with individual MPPT per string rather than one big unit. Costs more upfront but on a canal boat the shade management difference is massive.

Also worth looking at flexible panels from Renogy — keeps the profile low for low bridges. My mate runs them on his widebeam and reckons they've been solid for two seasons.

Don't ditch the genny entirely though, keep it as backup for winter mooring.

LizHunt | Posts: 312

Worth adding — roof space on a narrowboat is genuinely limited once you factor in cratch covers, ventilation cowls, and anything the previous owner's bolted up there. Your mate should do a proper roof survey before buying panels, not after. On our friends' 58-footer they ended up going portrait orientation with four 175W panels rather than the larger 200W landscape ones simply because of where the mushroom vents sat. Also @FormerTeacher makes a fair point about the marine environment — get panels with a proper IP68 junction box rating, the condensation and splashing will find any weakness sharpish.

@GazPrice done a similar job on a mate's 60-footer last summer. The real pain point nobody mentions is vibration — canal bridges, locks, general movement means your mounts need to be solid. Use proper marine-grade fixings, not the stuff that's fine on my shepherd's hut roof.

Also worth knowing: narrowboats run their engine to charge anyway, so solar works alongside that rather than replacing it. A decent Victron MPPT and 2-3 panels will meaningfully cut your engine hours though. Genny as sole solution gets old fast — noise, fuel, faff.

Totally doable retrofit, just plan the cable runs before committing to panel positions.

Deano88 | Posts: 847

@GazPrice mate, the genny vs solar debate on boats usually comes down to mooring habits more than anything. If your mate's planning long static stints — marina berths, winter tie-ups — solar pays for itself pretty quickly. But if he's constantly cruising, the alternator on the engine is doing half the work anyway, so the solar's basically topping up. I'd say do both, but size the solar sensibly given what @LizHunt said about roof real estate. Flexible panels are worth considering for the curves near the bow if he's short on flat roof. What's his typical usage like?