Anyone else finding their panels massively underperforming this winter?

Got a 400W setup on the shepherd's hut — two 200W Renogy panels wired in parallel, feeding into a Victron MPPT 75/15. Even on what passes for a "clear" day out here on the marsh I'm barely scraping 80-100W peak. Feels like something's off but also... maybe it's just January in the UK and I need to accept that?

Angle is fixed at about 30° facing south-ish (more like SSW if I'm honest). Been wondering whether tilting them steeper for winter would actually make a meaningful difference or if the low sun is just baked into the physics and there's nowt to do about it.

Victron app is showing the battery — a 100Ah Fogstar Drift LiFePO4 — sitting at 60-70% most days which is fine for my usage, but I had visions of being more self-sufficient through winter and it's not quite playing out. Curious whether anyone's found practical gains from seasonal adjustments or if I'm just romanticising what's possible up here between November and February.

@MarshLover what's your panel tilt angle? I'm on a motorhome so mine are flat-mounted on the roof and winter performance is genuinely dire — but I knocked up a simple tilting bracket for when I'm stationary and it made a noticeable difference.

Worth checking your Victron app too — the MPPT history will show you peak wattage achieved each day. Mine was showing suspiciously low figures until I realised one of my Anderson connectors had corroded and was dropping voltage before it even reached the controller.

Also — what's your Voc reading actually showing in the app on those "clear" days? Two 200W Renogy panels in parallel should still be pulling reasonable amps even in low winter sun. Wondering if there's a shading or connection issue rather than just the weather being rubbish.

Hey @MarshLover, totally feel your pain! Winter on the marsh sounds particularly grim for solar. Worth checking whether those 80W readings are at peak midday or averaged across the day — makes a big difference in diagnosing the problem.

One thing nobody's mentioned yet: have you checked for shading from low winter sun angles? Even a telegraph pole or tree that caused zero issues in summer can cast a shadow right across your panels from November onwards when the sun barely clears the horizon. With parallel wiring it won't cripple you quite as badly as series would, but it'll still nick a fair chunk of output.

Also worth giving the panels a proper clean — marsh environments can leave a surprising film of salt and grime that really knocks efficiency back. Sometimes something dead simple makes a noticeable difference! 🌞

Hey @MarshLover, one thing nobody's mentioned yet — have you checked your panels for that thin film of algae or lichen that loves damp coastal environments? On a marsh especially, you can get a greenish haze building up that's nearly invisible but absolutely kills output. Worth a proper clean with some diluted white vinegar and a soft brush. Also, at this latitude in December/January, even a "clear" day means the sun barely clears the horizon — you're potentially looking at an effective generation window of maybe 4-5 hours at a very low angle. Your Victron should be logging daily yield; have a look in the VictronConnect app and check whether the limiting factor is irradiance or something else. 80W from a 400W setup on a grey winter's day isn't actually disastrous, but there's likely room for improvement!

Hey @MarshLover, to add to what others are saying — have you looked at your actual irradiance figures for your location? Tools like PVGIS will show you that in December/January, southern England is often only getting 1-2 peak sun hours on a good day, sometimes less. So 80W from a 400W array isn't necessarily a fault — it might just be winter maths. That said, your Victron MPPT should give you decent logging through VictronConnect; worth pulling up the yield history to see if there's a specific day where output dropped suddenly (suggesting a wiring or panel issue) versus a gradual seasonal decline. What's your battery state of charge typically sitting at — are you actually running short, or is it mostly the numbers that are worrying you?

@MarshLover had the same grief with my shepherd's hut setup last winter. 80W from 400W rated on a "clear" December day is actually not that far off reality once you factor in the sun angle — we're talking maybe 15-20° above the horizon at noon in the UK right now. Your panels are basically seeing the sun at a terrible angle all day.

What tilt are your panels at? If they're mounted flat or close to it, you're losing a significant chunk before you've even started. Steepening to 50-60° in winter makes a noticeable difference. I knocked together a simple adjustable mount for mine — nothing fancy, just some angle iron from the local steelyard.

Also check the Victron app — it'll show your peak input clearly and you might find things are actually working correctly, just physics being miserable.

Great points from everyone already. One thing worth adding @MarshLover — have you checked your panel tilt angle recently? Winter sun sits so low in the sky that even a few degrees makes a dramatic difference. Ideally you want something closer to 60-65° from horizontal in December rather than the flatter summer angle. If your panels are fixed at say 30°, you're catching the light at a really oblique angle and losing a significant chunk of potential output. Some folks with shepherd's huts rig up a simple seasonal adjustment using hinged mounts — nothing fancy, just a couple of wooden props.

Hey @MarshLover, something worth checking that nobody's touched on yet — have you looked at your panel orientation and tilt angle? Winter sun sits really low in the sky here in the UK, sometimes barely 15-20° above the horizon at midday. If your panels are flat or only slightly tilted, you're losing a significant chunk of potential output compared to summer. Even propping them up to 50-60° for winter can make a noticeable difference.

Also worth double-checking your Victron app history — the MPPT will log your daily peak wattage, so you can see whether you're actually hitting a decent harvest window around solar noon or if it's trailing off earlier than expected. Living on the marsh you'll likely get horizon obstructions too, which compounds the low sun angle issue. What direction are your panels facing?