Anyone else finding their solar output absolutely rubbish this January compared to last year?

Just wanted to see if others are in the same boat. We've got a 400W panel setup on the roof of our static (two 200W Renogy mono panels in parallel), feeding into a 100Ah lithium via a Victron SmartSolar 100/30 MPPT. Last January I was regularly seeing 20–30Ah going in on a decent day. This month I've barely cracked 10Ah on most days, and yesterday the controller was reporting less than 5Ah by end of day. Battery was sitting at 68% by evening which is making me a bit nervous with the fridge and router running overnight.

I've checked the obvious stuff — panels are clean, no new shading issues, tilt angle is at about 35° which I know isn't ideal for winter but it's fixed mount so not much I can do. The Victron app history looks normal enough, no faults flagged. I'm wondering whether it's just been an exceptionally grim few weeks for solar irradiance across the UK or whether something's quietly going wrong with my setup that I'm not spotting.

Has anyone else seen a noticeable dip compared to the same period last year? And does anyone have a rough sense of what a realistic daily yield looks like for a 400W system in the north of England in January? Trying to work out if I need to panic or just accept that this winter is being particularly miserable.

Hey @HelenMoore, yeah it's been pretty grim here in Dorset too! My setup's been limping along most days. One thing worth checking though - have you had a look at the actual panel angle this time of year? The sun sits so low in January that even a few degrees adjustment can make a surprising difference to output. I tilted mine forward about 15° extra last week and picked up a noticeable improvement. Also worth checking for any moisture or condensation sitting on the panels first thing in the morning - I found that was robbing me of the early morning generation I desperately needed. What's your current tilt angle? 🌞

@HelenMoore January's been brutal this year, no question. I'm running 640W on my tiny house build (four 160W panels, two strings in series-parallel) and I've had days where I'm barely seeing 80-100Wh — panels are clean, angles are correct, just genuinely poor irradiance.

Worth checking your Victron app's historical data if you haven't already — the yield graphs make it easy to do a proper like-for-like comparison rather than relying on memory.

One thing I'd flag: at low winter angles, even a small amount of shade or soiling has a disproportionate effect on parallel strings. Might be worth temporarily wiring yours in series to see if output improves on clearer days.

Ultimately though, this January has just been genuinely grimmer than last — nothing you can really engineer around that.

Something I've noticed on the shepherd's hut this January is that the angle matters far more than the wattage when the sun sits so low in the sky. My panels are fixed at about 45° on the south-facing roof pitch, and even on grey days I'm pulling something useful compared to last winter when they were almost flat.

@HelenMoore with parallel panels on a static roof, I'd wager you're losing a fair chunk just from shallow incidence angle rather than cloud cover alone. Worth checking your Victron history logs — there's often a telling pattern in the yield data that shows whether it's genuinely worse cloud or something in the installation geometry.

Mine's a modest 300W into a Fogstar 100Ah, but that 45° pitch has been quietly earning its keep even through the murk.

@HelenMoore same story on the motorhome here. I'm getting maybe 10-15% of rated output on the really overcast days, which is frankly depressing when you're trying to keep a 200Ah Fogstar battery topped up.

One thing I'd flag specifically for your setup — parallel wiring means any shading on one panel drags the other down too. If you've got any winter shadows creeping across the roof (trees, nearby structures), that'll compound the seasonal misery.

Worth checking your Victron app history and comparing against last January's data if you've had it that long. Sometimes what feels worse actually isn't — January 2024 had a couple of decent bright spells that skewed expectations.

That said, I've genuinely had days this month where the SmartSolar barely registered above 8W. Just how it is up here in winter.

@HelenMoore mate, January in the UK is basically 31 days of the sun filing a sick note — my static's Victron MPPT laughs at me every morning when I check the app, showing about 8W from 600W of panels like it's doing me a personal favour. Tilted mine up steeper in December after years of stubbornness and honestly the difference on those rare bright days is the only thing keeping me sane. Fogstar battery at least holds what little charge I scrape together overnight, so there's that. Roll on February when the sun might occasionally remember we exist.

@PartnerBuild is onto something with the angle — I tilted my panels from 15° to about 45° back in November and it made a noticeable difference. Low winter sun needs a steeper pitch to hit the panels properly.

That said, even with the adjustment I'm still only seeing decent output in that narrow window around solar noon. Rest of the day is pretty grim.

One thing worth checking — are your panels accumulating any grime or moss? Surprising how much that kills output. Gave mine a proper clean with a soft brush last week and picked up maybe 5-8% more on a comparable overcast day vs the week before.

Still running on mains top-up more than I'd like tbh. That's just January reality with UK latitude.

@NotAnElectrician80 beat me to the sick note joke but mine's been on extended compassionate leave — narrowboat life means I can at least chug the engine for an hour and pretend I planned it that way.