Anyone else finding MPPT controllers massively underperform in UK winter conditions?

Picked up a Victron SmartSolar 100/30 back in September and paired it with two 200W panels wired in series (so 24V nominal system). Summer was brilliant — hitting 25-28A on decent days no bother. But since November I've barely seen it crack 8A even on the clearer days, and that's with the panels wiped down and angled up steeper to catch the low sun.

I get that we're only getting 6-7 hours of usable daylight up here in Liverpool and the irradiance is rubbish compared to July, but I'm wondering if I've got a setup issue on top of the seasonal drop. The VictronConnect app is showing VOC around 68-72V on cold mornings which seems about right, but the conversion to charging amps feels sluggish. Battery bank is two 100Ah LiFePO4 in parallel, usually sitting around 50-60% SOC when I start charging so it's not like they're nearly full and tapering off.

Has anyone done a proper comparison of their winter vs summer output figures with similar kit? And does shading from low sun angles hitting nearby obstacles make more difference than people realise — I'm in a terraced street so there's a fair bit of roofline shadow creeping in earlier than I'd expect. Wondering whether repositioning the panels or adding a third panel would actually move the needle much between October and February.

@Scouse16 your post got cut off but I'll address the obvious — yes, winter MPPT performance drops significantly in the UK, but it's not the controller underperforming, it's physics.

A few things worth checking:

• Low irradiance clipping: Your 100/30 is rated to 30A max. In winter, low sun angles mean you're rarely threatening that limit anyway
• VOC temperature coefficient: Cold panels actually produce higher voltage — worth verifying your series string doesn't exceed the 100V input limit on frosty mornings
• Shading geometry: Winter sun barely clears 15° elevation in the north of England — even minor obstructions cause disproportionate losses

On my shepherd's hut setup I dropped from ~85% efficiency in August to roughly 40-45% usable yield December-January. That's not the Victron failing — that's Merseyside in January.

What's your panel orientation and tilt angle? That's usually the first thing to optimise for winter gain.

Same setup in my garden office — two panels in series into a Victron SmartSolar. Worth checking a few things @Scouse16:

• What's your panel orientation? Even a few degrees off south kills winter output disproportionately
• Have you checked the VRM portal figures against actual irradiance data for your location? Sometimes the controller is doing its job fine but available solar is just genuinely dire
• Shade from low winter sun angles can be brutal — my neighbour's fence barely mattered in June but wipes out my morning generation November through February

What voltage is the array actually reaching at peak? If you're not hitting the panel Vmp consistently that's a different issue to the MPPT algorithm itself. Worth logging a few days on the Victron app before concluding the controller's the problem.

Something a lot of folk miss with UK winter solar — the irradiance is the real killer, not the temperature. Actually, cold clear days can boost your Voc beyond summer peaks, which is worth checking against your controller's input ceiling before anything trips out.

In my van build I've got a similar Victron setup and January surprised me with some genuinely decent charge sessions after a sharp frost — panels sitting at 39-40V open circuit when it was 2°C out.

The brutal truth is you're fighting 8-hour maximum daylight windows and predominantly overcast skies. I've found panel orientation matters enormously in winter — even a 10° tilt adjustment toward steeper angles made a noticeable difference when the sun barely clears the rooftops here.

What's your panel tilt currently, @Scouse16?

CraftyGrafter | 847 posts | ⭐ Regular Contributor

Worth adding to what @Gazza was getting at — your panels will actually produce higher voltage in cold conditions due to the negative temperature coefficient of Voc. So check your Victron app's history tab and see what peak voltages you're recording. If anything, winter can occasionally throw surprisingly punchy short bursts when the sun breaks through onto cold panels.

The real culprit in my experience is the sheer brevity of the useful solar window — we're talking maybe 4-5 hours of genuinely productive irradiance at best up here in December. I'd look at your daily Wh figures rather than peak amps, as that'll give you a more honest picture of what you're actually harvesting versus summer. What battery capacity are you running with it?