Anyone else struggling to get decent output from their MPPT controller in UK winter conditions?

I've had my Victron SmartSolar 100/30 paired with two 200W panels (wired in series, so 24V nominal system) on the roof of my Transit conversion since last March, and summer was brilliant — regularly hitting 20–25A on decent days. But since October it's been a different story. Yesterday we had a clear-ish day in the Peak District and I barely scraped 8A at peak, around midday. Panels are tilted at about 35 degrees, no shading, so I don't think that's the issue.

I've been digging into the VictronConnect app and the absorption and float voltages all look correct for my 200Ah lithium (BYD cells, 24V bank). The MPPT history shows the panel voltage sitting around 38–40V which seems reasonable for cold weather. I'm just not sure if 8A in December is actually about right for our latitude, or whether something is genuinely off with the setup. I've read that irradiance in the UK in winter can be less than 20% of peak summer levels, but that still feels low.

Has anyone got similar panel/controller combos and kept a log of their winter output figures? Would love some real numbers to compare against rather than just calculator estimates. Also wondering if it's worth experimenting with a steeper tilt angle — maybe 55–60 degrees — to better match the low sun angle. Anyone tried that on a van roof, even temporarily?

Chalky38 | Posts: 847

@StormyNomad yeah, winter in the UK is a different beast entirely mate. A couple of things that helped me massively — first, don't underestimate low-angle sun hitting dirty panels. Even a quick wipe-down made a noticeable difference to my output figures.

Also worth checking your battery temperature compensation settings in the VictronConnect app. Cold batteries need a higher charge voltage to actually accept a proper charge, and if that's not dialled in you're losing efficiency at both ends.

The other thing nobody mentions — those crisp cold clear days in January/February can actually push decent wattage if you're parked up with a good southern aspect. I sometimes reposition the van deliberately on those days. Every amp counts! What's your typical daily consumption looking like?

AndyJackson59 | Posts: 1,243

@StormyNomad Something worth checking that nobody's mentioned yet — have a look at your panel tilt angle. Most van builders just lay them flat on the roof which is fine in summer, but in winter the sun barely gets above 20-25° elevation here in the UK. Getting even a modest tilt towards the south can make a surprisingly big difference to your harvest. I knocked up a simple adjustable bracket system on mine using some aluminium angle from B&Q, cost me about a tenner. Also worth keeping an eye on your battery temperature — cold batteries accept charge differently and your Victron should ideally have the temperature sensor fitted if you haven't already done that. Makes a real difference to how the controller manages the charging curve in cold conditions.

CumbrianOffGrid | Posts: 1,203

@StormyNomad living up here in Cumbria I've had to make peace with grim winter output! One thing worth checking that nobody's mentioned yet — have you logged your panel voltage at dawn versus midday? In really cold clear mornings you can actually get higher Voc than the datasheet suggests, which occasionally trips the MPPT's upper input limit if you're pushing it. Flip side is the low irradiance days where the controller never properly locks onto the MPP at all and just dithers about.

Also worth enabling the Equalization or absorption fine-tuning in VictronConnect if your battery chemistry allows it — I found my SmartSolar was cutting absorption short on short winter days, leaving batteries chronically undercharged by February.

How's your panel orientation? Even a small tilt adjustment southward made a noticeable difference for me through December.