Anyone else running a mix of solar and alternator charging on a narrowboat? How are you managing the two sources?

Been living aboard my 57ft narrowboat for about three years now and I've recently upgraded the solar setup — two 200W panels on the roof feeding into a Victron SmartSolar 100/30 MPPT. Works brilliantly in summer but obviously the trees and low sun angle in winter means I'm heavily relying on the Beta 43 engine and a 115A alternator to top up my 400Ah of AGM batteries.

The issue I'm running into is prioritising charging properly. At the moment I've just got a basic split charge relay handling the alternator side, and I'm wondering if it's fighting with the MPPT when both sources are active at the same time. I don't think it's causing damage but it feels a bit inelegant and I'm not convinced the batteries are getting a proper absorption charge when both are running simultaneously.

I've been looking at the Victron Orion-Tr Smart DC-DC charger as a replacement for the split charge relay — seems like it would let the two sources play nicely together and give the leisure bank a proper charge profile from the alternator. Has anyone gone down this route on a boat specifically? Wondering whether the 30A version is enough or if I should be looking at the 50A, given a 115A alternator.

@VanHolly not directly applicable since I'm land-based (garden office and EV charging setup), but I run a similar dual-source situation — solar MPPT plus a secondary DC input — and managing charge priority between the two has been my biggest headache.

Curious what you're using on the alternator side? Are you running a B2B charger like the Victron Orion-Tr Smart, or going straight in? I'd imagine on a narrowboat the alternator output during cruising hours is substantial, and getting the two sources to play nicely without one fighting the other seems like it could get messy.

Does the SmartSolar 100/30 handle the handoff gracefully when the engine kicks in, or do you see any weird behaviour on the Victron app when both sources are active simultaneously?

Running almost identical to you on my own boat setup. The Victron comms are the real winner here — letting the SmartSolar and a Multiplus talk to each other via VE.Bus means they play nicely without fighting over state of charge.

One thing worth doing if you haven't already: set your alternator charging profile slightly lower than solar absorption voltage. Stops them competing when you're chugging along on a sunny day. Learnt that the hard way last summer on the Llangollen.

Also worth checking your alternator isn't getting cooked if you've got lithium — a Victron Cyrix or battery-to-battery charger like the Sterling Pro Batt Ultra between alternator and bank will save your alternator from trying to fill a big lithium void at full current indefinitely.

@VanHolly the one thing nobody mentions with combined alternator/solar on a narrowboat is alternator protection when the batteries are near full. If your SmartSolar has already pushed the bank to absorption and then you fire the engine, your alternator suddenly sees near-zero load demand and can spike. Worth fitting a Victron Cyrix-ct or at minimum checking your alternator has decent internal regulation.

Also on a 57ft roof you're leaving serious watts on the table with only 400W. Narrowboat roofs are actually decent real estate — I'd be looking at another two panels minimum.

Don't know what battery chemistry you're running but if it's lithium, ensure your MPPT charge profile and alternator both have a proper BMS disconnect strategy. Alternators hate sudden open-circuit disconnects from a BMS trip. Sterling make a decent alternator protection device specifically for this scenario.

@VanHolly great setup — I ran something similar on a 60ft trad stern for a couple of years. One thing worth mentioning that I don't see covered above: think carefully about your battery state when you're mooring up after a long cruise. If the solar has been doing good work all day and your bank is already sitting at 90%+, the alternator is going to hit a brick wall pretty quickly and you'll barely get any meaningful charge from the engine at all.

I ended up adjusting my absorption voltage slightly and timing shorter cruises for earlier in the day before peak solar hours. Also worth checking your SmartSolar absorption/float settings are properly coordinated with whatever the alternator regulator is doing — mismatched charge profiles between the two sources caused me some confusion early on.

Really interested in this thread — I'm in a similar situation with my tiny house/boat hybrid setup and constantly wrestling with the same questions.

@SolarJunkie you've got me curious now — what is the alternator protection issue you're hinting at? Presumably something to do with the lithium batteries disconnecting under certain conditions and leaving the alternator without a load?

I've been considering adding a Victron Orion-Tr Smart DC-DC charger between the alternator and the lithium bank rather than connecting directly — has anyone on a narrowboat gone that route? Seems like it would solve a few headaches at once.

Also wondering how people handle the priority logic — do you let the MPPT "win" when solar is strong enough, and only run the engine when genuinely needed? Or does the Victron ecosystem sort that automatically through the BMS comms?

Hey @VanHolly, lovely setup! One thing I'd add that nobody's touched on yet — if you're running the Victron SmartSolar, make sure you're using the VE.Direct cable to link it up with a BMV battery monitor if you haven't already. Having both your alternator input and solar visible in the same state-of-charge calculation makes a huge difference to how accurately the system manages charge cycles. Without it, your MPPT is essentially working blind to what the alternator's already put in, and you can end up with confused absorption/float transitions. I've got a similar dual-source setup on my 62ft semi-trad and the Victron app integration was genuinely the thing that tied it all together properly. Also worth checking your alternator isn't being asked to do too much heavy lifting in winter when solar drops off — alternator strain on older boats is a real concern. 🙂