Anyone else finding MPPT controllers massively underperform in the UK winter? Curious what you're seeing

I've got a 400W panel array (2x200W Renogy monos) wired in series feeding into an Epever Tracer 4210AN, charging a 200Ah AGM bank. Summer was brilliant — regularly seeing 25-30A on a decent day. But since October I've barely scratched 8-10A even on what I'd call a "bright" day, and yesterday we had full blue sky from about 10am and I only peaked at 14A around noon.

I know the sun angle is the big obvious factor, and I've got the panels at a fixed 30° tilt on the van roof which I understand isn't ideal for winter. But I'm also wondering if there's something off with how the Epever is handling things — the VOC is reading around 58-60V which seems healthy, and battery voltage is sitting at 12.4V before charge starts, so it's not like it's refusing to charge.

Has anyone experimented with steeper tilt angles for winter, even temporarily? I've seen people prop panels up with some kind of adjustable bracket but not sure how practical that is on a van roof. Also curious whether the Tracer 4210AN is generally well regarded for UK conditions or if there are controllers that handle low-light diffuse irradiance better.

@MistyMaker oh god yes, my cabin setup has been painful this winter. Though actually — pedantic point — it's not really the MPPT underperforming, it's just, y'know, physics. Less irradiance = less watts full stop.

What I have noticed though is the cold actually helps Voc creep up a bit, which is interesting. Panels run more efficiently at lower temps.

Your Epever should be fine honestly. My concern with your setup would be the AGM — they hate charging in the cold, acceptance rate tanks below about 10°C. That's probably where your "underperformance" is coming from rather than the controller itself.

Worth checking your battery temp and whether Epever has temp compensation enabled. If you've not got a battery temp sensor on there, that's worth sorting first.

@MistyMaker the thing nobody warned me about when I set up my garden office system was just how low the sun sits in the sky come November. I'm near Leeds and my panels are tilted at about 30° — fine for summer, but the winter sun barely clears the roofline opposite for maybe four hours.

What transformed things for me was remounting one array section at 60° for winter. Same Renogy panels, same Victron SmartSolar controller — I picked up nearly 40% more daily yield just from that angle change.

The other sneaky culprit in my setup was partial shading I hadn't even noticed in summer. Worth checking if any shadows are creeping across your panels between 10am-2pm when the sun's at its pathetic UK winter altitude. Even a tiny shadow on a series string absolutely murders your output.

@MistyMaker yeah narrowboat life really hammers this home. My 580W array on the Victron SmartSolar barely touches 8-10A on a typical grey January day.

The sun angle thing @MarkGibson mentions is brutal on the cut — trees and bridges shadow you constantly even when there is usable light.

What's helped me most is watching the voltage rather than amps. Even weak winter light can push decent voltage for longer than you'd expect, so the MPPT's still doing something.

Honestly though I just accepted diesel top-ups Nov-Feb rather than throwing more panels at the problem. At some point it's just physics innit.