Does anyone actually get useful output from a 100W panel in a UK winter?

I've had a 100W mono panel on my narrowboat since September and I'm starting to wonder if I made a mistake going so small. Through the summer it was brilliant — regularly seeing 5–6A into my 100Ah leisure battery on a clear afternoon. But now we're into January and I'm lucky to see 1–2A even at midday, and that's on a good day. Most days it barely registers.

I've got a Victron 75/15 MPPT controller which I know is decent kit, so I don't think it's a controller issue. Panel is south-facing at about 30° tilt on the cabin roof. I've been keeping it clean. My loads are pretty modest — a 12V compressor fridge (draws around 3–4A average), some LED lighting, and charging phones/laptop. The fridge alone is killing me through the night.

Is this just the reality of a single 100W panel at ~52°N in January, or is there something I'm missing? I'm seriously considering adding a second panel but space on the roof is tight. Wondering if anyone's been in a similar position and what you actually did about it — whether that's adding capacity, adjusting tilt, running a shore power hookup occasionally, or just accepting it and managing consumption differently.

@HarbourKate honestly, winter on a motorhome roof taught me more about UK solar reality than any YouTube video ever could.

Short answer: yes, but you have to reset your expectations completely.

My 100W panel on grey December days gives me maybe 8–15Ah across the whole day. Sometimes less. But here's the thing — that's not nothing. It's topping up what's there rather than doing the heavy lifting.

What I found made the biggest difference was panel angle. I picked up a cheap tiltable mount and pointing it more steeply south in winter genuinely recovered 30–40% more output compared to lying flat.

Also worth checking your controller settings — Victron SmartSolar will log your daily harvest history, so you can actually see what you're working with rather than guessing.

One 100W panel was always going to struggle solo through winter. That's the honest truth of it.

@HarbourKate my Fogstar 100Ah laughs at my 100W panel every December — it's basically a very expensive sky ornament until March.

@HarbourKate the hard maths nobody wants to hear: December in the UK you're realistically looking at 0.5–1.5 peak sun hours on a good day, and that's assuming your panel isn't sitting at some useless flat angle on a cabin roof collecting canal grime.

100W × 1.0 PSH = roughly 50–70Wh after system losses. That's keeping a 12V fridge ticking over for maybe three hours. Nothing more.

I've got 400W on my static at a decent 35° pitch and even I'm supplementing with a small genny through January. The physics simply doesn't favour us above 52° latitude in winter.

Worth checking your Victron MPPT history if you have one — the actual logged data tends to be quite sobering compared to what the panel manufacturers imply with their vague "seasonal performance" waffle.

@FormerTeacher those peak sun hour figures really sting when you see them written out like that.

Genuine question for the thread — does panel angle make a meaningful difference in winter specifically? I've got a 100W Renogy on my tiny house roof at a fairly flat pitch and I've always wondered whether propping it up steeper during the short days would actually move the needle, or whether the diffuse cloud cover makes the angle almost irrelevant anyway.

I've seen conflicting advice — some people say tilt it to 60° in winter, others say with UK overcast it barely matters because the light's coming from everywhere at once rather than a direct source.

Has anyone actually tested this with real figures rather than just theory? Would love to know if it's worth bodging together a tilt mount before next December.

@FormerTeacher those numbers hit hard when you're sitting on a boat watching grey skies for the third week running.

Living aboard a tiny house on water myself, I've found panel angle makes a surprising difference in winter — is yours flat-mounted or can you tilt it? Even propping mine up to 60° on a cold clear January day shifted output noticeably compared to lying flat.

Also curious whether anyone's found the Victron MPPT controllers genuinely squeeze more out of marginal winter light versus cheaper PWM units? I upgraded last spring and think I'm seeing better performance on overcast days but it's hard to isolate the variables properly. Could just be wishful thinking on my part.