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

I've been running a Victron SmartSolar 100/30 paired with two 200W panels (wired in series, so roughly 44V Voc into the controller) on my static setup in the Lake District, and I'm genuinely puzzled by what I'm seeing through the winter months. On a clear December day I'm getting maybe 15-20Ah into my 200Ah lithium bank, which feels low even accounting for the short days and low sun angle. The panels are tilted at about 50° to try and catch what little sun there is.

What's catching my eye is the absorption voltage. I've got it set to 14.2V for lithium, which my battery supplier recommended, but I'm wondering if the controller is spending too long in bulk and not enough time actually topping the bank off before it goes dark. On some days it barely seems to get out of bulk at all — presumably because the available power just isn't there to push the voltage up before sunset.

I've also noticed the controller occasionally reporting negative temperatures on the SmartSense dongle when it's really cold overnight — like -3°C last week — and I'm not sure if that's causing any odd behaviour with temperature compensation. I've got temp comp disabled as per the lithium settings, but still.

Has anyone running a similar setup in northern England or Scotland found any particular tweaks that have actually made a measurable difference? I'm half-tempted to add a third panel but want to rule out a settings issue first.

Ozzy97 | 📍 Yorkshire Dales | ⚡ Victron + DIY LiFePO4

@LakelandWanderer yeah the Lakes in winter is a tough ask! One thing that made a noticeable difference for me was adjusting the absorption voltage upward slightly for cold temperatures - lithium or lead acid? If you're on lead acid, the battery temperature compensation is crucial and often overlooked. Cold batteries need higher charge voltages to actually accept a full charge.

Also worth checking your panel orientation - even 10° off from optimal kills output on those low winter sun angles. I dropped mine from 35° to closer to 55° tilt for winter and saw meaningful improvement.

What's your actual logged Voc on cold mornings? Sometimes the controller's MPPT algorithm takes a while to "hunt" to the true peak on rapidly changing cloud cover days. Victron's algorithm is decent but not perfect.

Taffy55 | 📍 Mid Wales | ⚡ Renogy + Pylontech

Something worth checking that doesn't get mentioned enough - your absorption voltage setting. In cold weather LiFePO4 cells actually want a slightly lower absorption voltage, but lead-acid benefits from going a touch higher to compensate for reduced chemical activity. I was scratching my head for weeks until I realised my controller was using summer-programmed settings through December.

Also, have you enabled the temperature compensation feature on the SmartSolar? If you've got the optional temp sensor attached it'll automatically adjust charge voltages, which made a noticeable difference for me here in Wales. We get similar grim overcast days to the Lakes.

The Victron app lets you monitor exactly what absorption/float phase the controller is entering - worth logging that data for a few days to see what's actually happening. @Ozzy97's point about the Lakes being brutal is spot on mind!

Lee1996 | 📍 Array | ⚡ Static Caravan

One thing that made a noticeable difference for me was dropping the absorption voltage down slightly during winter — batteries just don't need to be hammered to full absorption when they're cold and you're barely pulling decent current anyway. Also worth checking your panel tilt angle if you haven't already. I shifted mine to a steeper pitch over winter and picked up maybe 15-20% more on low-sun days just from hitting that lower sun angle better.

The other thing with Victron specifically — make sure you've got the temperature compensation dialled in properly via the app. If you're not using a SmartBattery Sense or the VE.Smart networking, the controller is basically guessing at battery temp, which in a cold static can be way off.

PhilPowell | 📍 Derbyshire Peak District | ⚡ Victron SmartSolar + LiFePO4

Good thread this. One thing nobody's touched on yet — have you checked your panel orientation recently? Sounds obvious but in winter the sun barely clears 20° elevation up your way, so even a small adjustment toward steeper tilt can make a meaningful difference to what the MPPT actually has to work with in the first place. I shifted mine from 30° to 50° around November and saw a noticeable improvement in those brief midday windows.

Also worth checking the MPPT history in the Victron app — look at your daily yield graph and see whether you're genuinely hitting absorption at all. If you're not, tweaking absorption voltage settings is largely academic. Sometimes the issue is simply irradiance rather than controller behaviour. @Taffy55's point about absorption is solid but only really applies if you're actually getting there!