Anyone else struggling to get decent output from their panels on cloudy UK days — tips for squeezing more out of a MPPT controller?

I've had my 200W Renogy panel paired with a Victron SmartSolar 100/20 for about eight months now, mostly running a small off-grid setup at our place in the Peaks. Summer was brilliant — regularly seeing 150-170W on a clear day — but now we're heading deeper into autumn I'm lucky to scrape 40-50W even at midday. I knew it would drop off but honestly wasn't prepared for just how dramatic the difference would be.

I've been playing around with the absorption and float voltage settings in the VictronConnect app, and I've also repositioned the panel to a steeper tilt angle (around 55°) to try and catch the lower sun. That's helped a little but not as much as I'd hoped. I'm also wondering whether my panel orientation is part of the problem — I'm fixed due south but there's a line of trees to the south-west that starts shading the panel from about 2pm onwards.

Has anyone found specific MPPT settings that make a noticeable difference in low-light or diffuse conditions? And is partial shading as catastrophic as some people suggest, or does the Victron handle it reasonably well? Would love to hear what others are doing to keep their systems ticking over through a grey British winter.

Finn1975 | 847 posts

@SarahLewis great setup choice — Victron's absorption/float tuning makes a real difference in low light. One thing worth trying: go into the VictronConnect app and tweak your absorption voltage slightly lower for winter. UK diffuse light rarely pushes panels hard enough to justify the standard absorption threshold, so the controller ends up hunting rather than harvesting.

Also check your panel angle — steeper tilt (50-60° rather than the typical 30°) genuinely helps in winter when the sun's barely clearing the horizon, especially up in the Peaks where you'll be losing morning and afternoon light to the hills anyway.

Finally, make sure your battery temperature compensation is enabled if you're running lead-acid — cold batteries need higher charge voltages to actually accept a decent charge.

What battery chemistry are you running?

CoastalCruiser | 1,203 posts

@SarahLewis Living on the coast I deal with this constantly — low-light performance really comes down to keeping your panel voltage as high as possible relative to your battery bank. A few things that helped me:

Check your cable runs are keeping voltage drop minimal — even a small loss hurts badly on dull days when you're already scraping single-digit amps. Worth recalculating with a voltage drop calculator.

Also, in the Victron app try enabling the "Low power mode" setting and have a look at your tail current threshold — lowering it slightly means the controller moves to float more efficiently when generation is poor.

Finally, don't underestimate panel angle adjustments in winter. A tilt closer to 60° can genuinely recover 15-20% on those flat grey November days compared to a summer-optimised angle.