Fitting solar to a 35ft narrowboat — where do I even start?

Just picked up a 35ft narrowboat and want to get off the grid as much as possible. Currently it has a single 110Ah leisure battery that the previous owner was running off the engine alternator. That's clearly not going to cut it for anything serious.

I'm thinking a 200-400W panel setup on the roof with a decent MPPT controller — been looking at Victron SmartSolar as I already use one on my van build. Battery-wise I'm torn between a couple of Fogstar Drift 100Ah lithiums or going AGM to keep costs down. The boat has a 12V system throughout.

Main loads are fridge, lighting, phone/laptop charging, and a small inverter for occasional 240V stuff. No washing machine or anything daft. Wondering if 200Ah lithium is actually enough or whether I should just go 300Ah from the off and avoid regret.

Has anyone actually done a narrowboat install rather than a campervan? Curious whether the challenges are meaningfully different — condensation, cable runs, that sort of thing. The roof space looks decent but I've no idea whether standard rigid panels survive the locks and low bridges without getting smashed.

Del6 | Posts: 847

@T6Project Congratulations on the boat! Good starting point is working out your actual daily consumption before buying anything — narrowboaters often underestimate how much a 12V compressor fridge alone pulls.

For a 35-footer you've realistically got maybe 200-250W of roof space depending on how much is taken up by the chimney flue, vents, and any cratch cover. Two 100W panels in parallel is a sensible beginner setup.

That single 110Ah battery needs replacing sharpish regardless — you shouldn't really draw it below 50% so you've only got 55Ah usable. Most liveaboards or serious cruisers run 200-400Ah of leisure batteries minimum.

What's your use case — weekend trips or extended cruising? That changes the answer quite a bit. Also worth knowing if you've got a 240V inverter requirement or purely 12V loads.

HarryMorgan | Posts: 1,203

@T6Project Great purchase! To add to what @Del6 is getting at — before you size anything, spend a few days actually living aboard and noting what you're running and for how long. That single 110Ah is almost certainly undersized for comfortable liveaboard use, even part-time.

On a 35-footer you've realistically got roof space for 3-4 panels depending on hatches and vents. Worth measuring carefully and checking for any tunnel height restrictions on your local waterways before committing to panel thickness/profile.

Also factor in that canal-side trees cause significant shading issues that land installations don't face — MPPT controllers handle partial shading far better than PWM, so worth the extra spend from the outset. What's your typical mooring situation — rural or more urban towpath?

QuietHiker | Posts: 312

@T6Project A narrowboat roof is basically a free solar farm you've been ignoring — typical 35ft gives you 3-4 panels easy, just mind the mushroom vents unless you fancy a very ventilated Victron install. Single 110Ah battery is genuinely embarrassing; even my garden office laughs at it. Look at a Fogstar 200Ah lithium as a starting point, pair it with a Victron SmartSolar MPPT, and suddenly you're living like a king on the cut rather than rationing the kettle.

Trevor1986 | Posts: 2,156

@T6Project Welcome to the rabbit hole! Solid advice above already. One thing worth adding specifically for narrowboats — watch your roof profile carefully before committing to panel sizes. Those traditional swan-neck tillers and roof vents can create more shading than you'd expect, and shading even a corner of a panel kills output disproportionately if they're wired in series. Also worth thinking about whether you're cruising regularly or more of a marina liveaboard, as that changes things massively. Regular cruising means your alternator is genuinely contributing; marina life means solar and/or shore power does the heavy lifting. A 35-footer can realistically fit 400-600W depending on layout. What's your typical usage — are we talking lights and phone charging, or do you want a 12V fridge and inverter in the mix?