Narrowboat 12V system keeps browning out on the Ashby Canal — solar not keeping up?

Been living aboard a 57ft trad stern narrowboat for the past two years, moored semi-permanently near Hinckley. Running a 400Ah Fogstar Drift 12V lithium bank with a 600W solar array (three 200W Renogy panels in series-parallel) feeding through a Victron SmartSolar MPPT 100/30. Should be plenty for our modest loads — fridge, LED lighting, a couple of phone/laptop chargers, and a small inverter for the wife's sewing machine.

Problem is that through autumn and winter, particularly on the overcast stretches of the Ashby, we're seeing the system drop to around 20-30% SoC by early evening even when we've had what felt like a reasonable day. The Victron app is showing bulk charge not completing until mid-afternoon on grey days, sometimes not at all. We've got a B2B charger (Sterling Pro Charge B 12/12-30A) running off the engine alternator, but we're only cruising 3-4 hours a week at the moment.

Wondering whether anyone else on a permanently-moored or low-mileage boat has tackled this seasonal shortfall? I'm considering adding a small Honda EU22i generator for top-up charging via a Victron MultiPlus 12/1600, but unsure whether that's overkill. Alternatively, a fourth panel if I can find roof space. What's working for people over winter?

BirchDaz | Member

@DefenderWanderer the Ashby's notorious for tree-lined stretches near Hinckley — I'd wager shading is hammering your actual yield far more than the panel specs suggest. 600W on paper can easily drop to 150-200W effective on a grey December day with partial shading thrown in.

Few things worth checking: are your three panels wired in series, parallel, or series-parallel? If series and one panel's shaded, the whole string suffers badly. An MPPT controller with individual panel optimisers, or rewiring to parallel, can make a significant difference on a boat.

Also worth logging actual amp-hours in versus out over a few days rather than relying on voltage alone — gives you a proper picture of the real deficit before throwing more panels or battery capacity at it.

What's your main consumption drawing it down — inverter loads, a diesel heater's control board, something else?

SomersetNomad | Member

@DefenderWanderer 600W nameplate on a canal that's essentially a tunnel of alder and willow is largely decorative, I'm afraid. The Ashby above Hinckley gets maybe 3-4 peak sun hours on a good summer day in open water — factor in cell-level shading losses and you're probably harvesting 40-50% of that.

More pressing question: what's your B2B charger situation when the engine runs? If you're relying solely on solar, your 400Ah Fogstar needs roughly 80A input to charge properly. Three panels in series-parallel through a decent MPPT helps, but check your controller's shading algorithm — some cheaper units capitulate entirely when even one cell shadows.

What's your daily consumption figure? Without that number, we're all just guessing in the dark — which, given your brownouts, seems rather appropriate.

ForestDaz | Member

@DefenderWanderer 400Ah Fogstar is doing nowt for you if your Victron MPPT charge controller is undersized for the actual harvest — what's the controller rated at, because I've seen lads with 600W panels strangled by a 30A controller and wondering why their batteries are perpetually sulking like a teenager. Sort your wiring losses too — 12V over any meaningful cable run is basically volunteering to heat copper rather than charge batteries. Static caravan sorted me out: I just accepted winter meant a generator, and you living on the Ashby Canal in what amounts to a leafy tunnel should perhaps reach the same mature acceptance and stick a decent Victron Multiplus in the equation for shore power backup.

Mel1980 | Member

@DefenderWanderer mate, the Ashby Canal is basically a giant hedge with a ditch running through it — your panels are generating enough electricity to charge a wristwatch.