Anyone know if a 200W panel is enough to keep a 12V leisure battery topped up over winter?

Running a basic setup on my narrowboat — single 110Ah Fogstar lithium and a 200W panel on the roof. Works brilliantly June through September, barely have to think about it.

But winter's got me second-guessing myself. We're talking maybe 2–3 hours of usable sun on a clear day here in the UK, and half of December feels like it's just overcast permanently. Even with a good MPPT (running a Victron 75/15), I'm wondering if 200W is actually doing enough meaningful work or just tickling the battery.

My loads are pretty modest:

• LED lighting
• 12V compressor fridge (biggest draw by far)
• Phone/laptop charging
• Occasional water pump

No heating off the battery — got a diesel for that.

Anyone actually monitored their winter output closely? I keep reading that people say "it's fine" but I suspect that depends heavily on how much you're drawing and whether you're moored somewhere with decent southern exposure. My current spot has trees to the southwest which won't help.

Wondering if I should just throw a second panel on or whether there's a smarter fix — tilt mount to steepen the angle maybe? Has anyone used those adjustable roof brackets worth recommending?

Would genuinely like to see some real winter numbers from people rather than the usual "should be okay" answers 😄

@VitoSolar yeah winter on a boat is rough for solar — low sun angle plus you're probably sat in a marina with trees or other boats throwing shade half the day.

200W into a 110Ah is tight. I run a shepherd's hut and even with decent sky exposure I was down to maybe 20-30% capacity on grim December days.

Honestly a small backup charger hooked to shore power (if you've got it) or even a decent DC-DC from the engine if you're moving at all — that saved me more than adding panels would've done.

If you can add another panel though, even a cheap Renogy 100W chucked on awkward mounting, the difference is real. Two smaller panels at different angles beats one big one in winter.

@VitoSolar the angle problem is brutal on narrowboats specifically — that flat roof mount means you're losing maybe 60-70% of theoretical output on a December day even without shading. I ran a similar setup on my river cruiser and found a 200W panel was barely pushing 15-20Ah on a decent winter day, sometimes under 10Ah when overcast.

The real question is what your daily consumption looks like. If you're running lighting and a 12V pump only, you might scrape through. But the moment you add a diesel heater controller, phone charging, or any 240V inverter use, you'll be discharging faster than you're replenishing.

Practical suggestion: tilt your panel even 20-30° using a simple aluminium bracket — makes a measurable difference in winter sun angles. Also worth checking your Fogstar's low-temperature cut-off settings if charging in near-freezing conditions.

200W in December in the UK might yield you 40–60Wh on a decent day — that's roughly 3–5A into your Fogstar, which is fine if you're not drawing much, but the moment you add a pump, heating controller, or any lighting you're in the red before lunch.

Crunch your actual daily loads first (Victron's app if you've got any of their kit, or even a cheap ammeter clamp), because "will it cope" entirely depends on consumption, not just generation.

My money's on adding a DC-DC charger wired to your engine alternator for winter top-ups — run the engine an hour every couple of days and you're sorted without bolting another panel somewhere awkward on a narrowboat roof.

What @FormerCop said is spot on, but here's the thing nobody mentions — consistency kills you more than the low wattage. Three grey days back-to-back in January and even a disciplined 110Ah lithium starts looking sorry for itself.

In my van I solved this by keeping a small B2B charger plumbed in for whenever I'm moving. On a narrowboat you've got a cracking advantage there — that engine running the locks is basically free charging. Lean into it.

Also worth checking: is that 200W panel actually tilted at all? Even propping the rear up 30° with a bit of angle iron over winter makes a noticeable difference. I did exactly this on a mate's canal boat last February and we picked up nearly 40% more harvest on sunny days just from that daft little fix.