Solar on a narrowboat — worth the faff vs just running the engine?

Been looking into fitting a small solar array on my narrowboat and wondering if anyone's actually done the sums on whether it's worth it compared to just running the engine or a generator for an hour each day.

I've got a 12V domestic bank — currently two 110Ah AGMs wired in parallel — and the boat sits on a towpath mooring in the Midlands where it gets a reasonable amount of sun in summer but obviously the roof is narrow and cluttered with vents and the chimney stack. Realistically I'm thinking two 175W Renogy panels in landscape orientation, maybe 350W total.

Would a Victron SmartSolar MPPT be overkill for that sort of setup, or is it the obvious choice? I've seen the 100/30 mentioned a lot on here. Also wondering whether AGMs are even worth charging via solar or if this is the nudge I need to upgrade to a Fogstar Drift LiFePO4 — the 200Ah seems to come up constantly on campervan builds.

Has anyone fitted solar on a narrowboat specifically? The roof access and shading from bridges must make it a different beast to a static or van setup.

Solar on a narrowboat makes my static caravan setup look positively landlocked with envy — but yes, do the sums: engine hour = roughly £1.50 in diesel plus the noise, the fumes, and your neighbours on the towpath giving you the look™.

A couple of Renogy 175W flexi panels and a Victron MPPT will quietly top your batteries all day while you're actually enjoying being on the water rather than working on it.

The "faff" is a one-time weekend job; the diesel bill is forever.

NorfolkSolar | 847 posts

@SprinterWanderer the key thing people overlook is running hours. If you're cruising regularly, your alternator's doing a decent chunk of the work anyway — solar really earns its keep on those static mooring days when you're just living aboard without moving.

On a typical UK narrowboat roof you can realistically fit 400-600W, which on a reasonable summer day gives you maybe 2-3kWh. That's your fridge, lighting, phone charging sorted without touching the engine.

The honest answer though: it's not either/or. Solar handles the slow background trickle, engine covers bulk charging when you're moving. They complement each other brilliantly.

Factor in that diesel isn't getting cheaper, and a decent flexible panel setup pays itself back within 3-4 years in my experience. What's your current battery bank looking like?

@SprinterWanderer coming at this from a shepherd's hut background rather than narrowboat specifically, but the battery chemistry question matters enormously here — lithium (particularly LiFePO4, something like Fogstar Drift cells) will absorb solar bulk charge far more efficiently than AGM, which means your panel-to-usable-energy ratio looks completely different depending on what's sitting in your bilge.

The calculation that actually matters: what's your daily consumption in Ah, what's your typical mooring situation (shaded towpath vs open canal), and how many hours are you genuinely cruising vs stationary?

Running the engine purely for charging is roughly 1–2A per hour at 12V per litre of diesel — spectacularly inefficient. Even a modest 200W Renogy panel on a south-facing tiller area will outperform that on a reasonable UK summer day without burning fuel or disturbing your neighbours at 7am.

OwenYoung83 | 312 posts

@SprinterWanderer done exactly this on my 57ft trad last summer — fitted 400W across the roof and genuinely haven't run the engine purely for charging since May. The thing people miss is the cumulative benefit on overcast days; it's not zero output, it's just modest. Even a dull British drizzle day I'm pulling 40-60W.

Main consideration for narrowboats specifically: roof space is awkward with vents, chimneys and handrails eating into your usable area. Flexible panels are popular but I'd honestly push back on those — rigid panels with proper tilt mounts give noticeably better performance.

What's your mooring situation? If you're predominantly static the maths look very different compared to continuous cruising where the alternator's already doing decent work underway anyway.