Anyone else running a Victron SmartSolar on a narrowboat with a 12V domestic bank?

I've just finished wiring up a 400W solar array on the roof of my 57ft narrowboat — two 200W panels in series running into a Victron SmartSolar MPPT 100/30. Domestic bank is four 110Ah AGM batteries (440Ah total), separate from the 120Ah starter battery. Seemed straightforward enough on paper but I'm getting some odd behaviour once the bank hits absorption stage — the controller keeps dropping back to bulk for 10-15 minutes at a time, even on a decent sunny day.

I've checked the wiring and the connections look solid. Cable run from the controller to the bank is about 2.5 metres of 16mm² so voltage drop shouldn't be the issue. I've got the battery type set to AGM in the VictronConnect app and absorption voltage is sitting at 14.7V. Wondering if the issue might be the way canal vibration is affecting the connections over time, or whether my absorption time settings are too aggressive.

Has anyone else dealt with this on a liveaboard setup? I'm also curious whether anyone's moved from AGM to lithium on a narrowboat and whether the engine alternator side of things became a nightmare to manage — that's probably my next headache if I ever make the switch.

Hey @LutonDream, nice setup! One thing worth checking — with two 200W panels in series you'll want to confirm your open-circuit voltage doesn't climb too high on a cold morning. Voc stacks up quickly in series, and on a crisp winter day it can spike noticeably above the rated figure. The 100/30 handles up to 100V input, so you're likely fine, but worth running the numbers with a temperature derating calculator just to be certain.

Also with AGMs on a boat, make sure your absorption and float voltages are dialled in correctly — AGMs can be fussier than lithium about being properly charged without overcharging. The VictronConnect app makes tweaking those parameters dead straightforward. What brand are the AGMs? Some have slightly different charge profiles worth matching.

@Victron_Pro is right to flag the Voc issue — worth doing the cold temperature calculation properly. Take your panel's Voc, multiply by 1.25 (worst-case correction for ~-10°C), and confirm it stays under the 100V input limit on that controller. Narrowboats moving through unshaded countryside on a cold January morning can catch people out.

One practical thing I'd add from my own fixed installation experience — on a boat that's moored under trees or bridges regularly, consider whether series wiring is actually working against you. Partial shading kills the whole string. Parallel at 12V loses some efficiency but handles patchy shade far better with a 100/30.

Also double-check your cable runs. Narrowboat roofs get warm in summer and the conduit situation is often improvised. Appropriate cable ratings matter more than people realise.

Great setup @LutonDream! Once you've sorted the Voc calculation that @Victron_Pro and @CarlBaker are flagging, you should be in good shape. One thing specific to narrowboat life worth mentioning — keep an eye on shading from bridges and locks. Even partial shading on one panel in a series string can hammer your output significantly. If you find it's a recurring problem on your regular routes, it might be worth looking at whether parallel wiring would suit you better, or adding individual panel optimisers. Also, with four 110Ah AGMs that's 440Ah total — your 30A controller should handle the charging nicely at that bank size. Are you running a BMV battery monitor alongside it? The Victron ecosystem really comes into its own when you've got the SmartSolar talking to a BMV or SmartShunt via Bluetooth. Makes a real difference knowing your actual state of charge.

Been running a near-identical setup on my motorhome for two seasons now, so this is familiar territory.

One thing nobody's mentioned yet — on a narrowboat specifically, shading is brutal. Bridges, trees, lock-side structures... if your panels are in series and one gets partially shaded, your output craters compared to a parallel configuration. The 100/30 handles both fine voltage-wise, but worth considering whether series actually suits canal life.

Also, four 110Ah AGMs at 12V gives you roughly 220Ah usable (keeping above 50% DoD). Your 400W array can theoretically replenish that in a decent summer day, but AGMs genuinely suffer if you're regularly hammering them. I'd be watching that bank closely and budgeting mentally for a LiFePO4 swap within a couple of years — Fogstar Drift cells have made that financially realistic now. Just saying. 😄