Anyone else struggling to get decent output from their panels in winter? Tips welcome

I've been running a 400W setup on my static caravan in North Yorkshire for about eight months now — two 200W mono panels wired in series going into a Victron SmartSolar 100/20 MPPT. Over summer I was regularly seeing 250–300W actual output on a good day, which felt brilliant. Now we're into December I'm lucky to scrape 80W even when it's not overcast, and the battery (a 100Ah lithium) is barely hitting 70% by end of day.

I know low sun angle is a massive part of it up here — we're at about 54°N so the panels are already mounted at a fairly steep pitch (around 40°) on a south-facing roof. I've been keeping them clean and checking the Victron app obsessively. The MPPT history shows the bulk charge is cutting out really early in the afternoon, which makes me think the voltage is just collapsing too soon.

Has anyone in a similar latitude actually added extra panels just to cope with winter, or is that just throwing money at a problem that won't fully go away? I'm also wondering whether wiring a third panel in parallel rather than series would make any difference on these low-irradiance days. Genuinely not sure if I'm missing something obvious or if this is just the reality of solar in northern England.

@HollyGraham83 North Yorkshire winters are brutal for solar — low sun angle kills output more than cloud cover does tbh.

Few things that helped on my motorhome setup:

• Tilt your panels if you can — even a cheap adjustable mount makes a noticeable difference in Dec/Jan
• Check your voltage in the morning before load kicks in — series wiring at least keeps Voc decent in low light
• Keep panels squeaky clean, grime + frost residue is worse in winter

Also worth logging via the Victron app — you'll see exactly when you're getting usable harvest. Mine peaks around midday for maybe 2-3 hours max at this time of year.

Realistically on a static you might want to look at a small wind turbine to complement it. Solar alone in winter up north is a tough ask.

@HollyGraham83 curious what tilt angle your panels are sitting at? Fixed flat mounts are fine in summer but you can lose a surprising amount in winter when the sun barely gets above 20° elevation. Even propping them up to 60° made a noticeable difference on my garden office setup — went from barely tickling the battery to actually getting usable charge by midday.

Also worth checking your Victron app for the absorption/float logs — are you even reaching absorption voltage on short winter days, or is the controller just sitting in bulk all day? That'll tell you whether it's a generation problem or something else going on.