Anyone else struggling to get decent winter output from roof-mounted panels on a static caravan?

I've got two 200W mono panels on the roof of my static, wired in series giving me a 24V nominal setup, running into a Victron SmartSolar 100/30 MPPT. In summer it's brilliant — hitting 350–380W on a good day and topping my 200Ah lithium bank up by early afternoon. But now we're into November I'm barely seeing 40–60W even at midday on a clear-ish day, and the battery's struggling to get above 80% most days.

I know low sun angle is a big part of it — I'm up in North Yorkshire so we're talking maybe 17–18° solar elevation at noon right now. The panels are flat-mounted with no tilt, which I suspect is killing me. I've been looking at adjustable tilt brackets but the static has a fairly low-pitched roof and I'm not sure what angle would actually be worth the hassle versus just adding a third panel flat.

Has anyone done a proper comparison between adding tilt versus adding more panel area for winter gains? I can see arguments both ways and the Victron app data is there if useful — happy to share some screenshots of the yield history if that helps anyone give a steer.

Reply by Nick1982:

@JackieScott — totally feel your pain on this one. The big thing people often overlook with statics isn't just the low sun angle in winter, it's the shading from neighbouring vans. Even a tiny shadow across one cell can absolutely murder your output, especially in a series string like yours.

Have you checked what voltage your Victron is actually seeing first thing in the morning on a clear day? A cold, clear December morning should still give you a decent voltage spike before irradiance drops it back down. That'll tell you if your panels are fundamentally healthy or not.

If shading is the culprit, it might be worth considering whether you could rewire to parallel instead — you'd lose some voltage but become much more shade-tolerant. Your SmartSolar 100/30 would handle it fine.

@JackieScott — the cruel irony of a static is you're stuck with whatever angle the roof gives you, which on most park homes is optimised precisely for not catching winter sun.

On my narrowboat I cheat by occasionally mooring on a south-facing bank and tilting my panels on their hinges — you don't have that luxury.

Worth knowing: at this latitude in December, even a perfectly aimed panel is working with roughly a third of the peak sun hours versus June. Your 400W array might realistically yield 200–250Wh on a decent winter day. That's not your kit failing — that's geometry and the Earth's axial tilt being deeply inconsiderate.

If your static's pitch allows it at all, even a cheap tilt bracket to get panels closer to 60° in winter makes a measurable difference. Renogy do reasonable adjustable mounting kits without requiring a second mortgage.

@JackieScott — one thing worth investigating that nobody's mentioned yet: panel soiling and moisture film in winter massively compounds the low-irradiance problem. I did a controlled experiment on my shepherd's hut setup last January — wiped one panel down with a microfibre and deionised water, left the other. The clean panel was producing roughly 12–15% more on overcast days specifically, because diffuse light is far more sensitive to surface contamination than direct summer sun.

Also worth checking your series string voltage against the SmartSolar's MPPT window on cold mornings — two mono panels in series can spike well above nominal Voc in sub-zero temps. The 100/30 handles up to 100V input, so you're likely fine, but worth logging via the VictronConnect app to confirm you're not clipping.

Worth adding — have you checked your battery state of charge at the start of those winter days? I found my setup was throttling output because the Fogstar lithium cells were already near full from the previous day's residual. The Victron was doing exactly what it should, just not what I wanted it to do.

Also, with panels in series at 24V nominal, your Voc in cold weather will spike noticeably — not a problem for the 100/30 but worth logging in the VictronConnect app to see what's actually happening at the MPPT input. Sometimes the numbers tell a different story to what you'd expect.

@JackieScott Two 200W panels on a static roof in a British winter is basically just an expensive way to watch clouds go by — tilt mounts from Renogy saved my sanity, even a 15° adjustment off the factory pitch made a noticeable difference on my van according to the Victron app.

@JackieScott something I'd flag that hasn't come up yet — have a look at your wiring and connections going into the controller, particularly where they exit through the roof. On static caravans those cable entry points can let in moisture over time, and even a bit of corrosion or a slightly loose MC4 connection introduces resistance that'll really bite you in winter when your voltage margins are already tight. I found a dodgy connector on mine that looked absolutely fine visually but was losing me meaningful wattage. Also worth double-checking that your Victron app is showing healthy battery voltage under load — if it's sagging more than expected you might have a connection issue rather than purely a solar generation problem.

@JackieScott One thing worth considering is your panel angle. Static caravan roofs are typically pretty shallow — often only 10–15° — which is actually decent for summer when the sun's high, but in winter you really want something closer to 50–60° to catch that low sun properly. If you can physically access the roof safely, even a simple tilting bracket arrangement to prop the panels up steeper during the darker months can make a surprisingly noticeable difference to your daily harvest. Some folk see 30–40% improvement just from reanglin them seasonally.

@JackieScott Worth checking your SmartSolar app data for the irradiance hours you're actually getting vs. expecting. In winter the UK typically delivers 1–1.5 peak sun hours daily — your 400W array is realistically yielding 400–600Wh on a decent day, less in overcast conditions.

One thing nobody's mentioned: partial shading losses are savage in series strings. One panel shaded clips the whole string's output. If nearby trees or the caravan's own roof vents are casting shadows even briefly, consider rewiring to parallel — your Victron 100/30 handles the lower voltage comfortably.

Fogstar or similar lithium cells also accept charge far more efficiently at low temperatures than AGM, which derate significantly below 10°C.

Hey @JackieScott, something nobody's mentioned yet — have you checked whether there's any shading creeping in during winter that wasn't an issue in summer? The sun sits much lower in the sky from November through February, so even a nearby tree, telegraph pole, or neighbouring static that caused zero problems in June can suddenly be casting shadows across your panels for hours each day. With series wiring, one shaded cell can drag the whole string down significantly. Worth walking round at midday on a clear day and having a proper look. Bypass diodes help but they're not a complete fix.

The shallow roof angle is the real killer in winter. My cabin panels are mounted on a ground frame I knocked together from 40mm steel box section — adjustable tilt, so I steepen them up around October and flatten them back in April. Night and day difference in December.

On a static you're not going to do that, but even propping the rear edge up a few inches with a proper mounting bracket makes a measurable difference. Renogy and a few others sell tilt kits that'll bolt onto existing roof rails without too much grief.

You're never going to match summer figures, but you can claw back a fair bit.

@JackieScott The series wiring is worth revisiting for winter conditions. With two panels in series you're doubling voltage but if one panel catches even marginal shading — a chimney shadow at low solar angles, frost on a corner — the whole string suffers disproportionately. Parallel wiring with your 100/30 would keep Voc within range (roughly 22–24V open circuit per panel) and give you better partial-shading resilience. I rewired my own setup parallel last November and recovered a noticeable chunk of those grim December hours. Also confirm your SmartSolar is on the correct battery preset — absorption voltage misconfiguration quietly robs you of usable harvest.