Anyone else finding their MPPT controller readings wildly off this winter compared to summer?

My Victron SmartSolar 100/30 has been giving me some head-scratching numbers lately. Running two 200W panels in series on our static caravan setup in North Wales, and I'm seeing bulk charging barely kick in before it drops straight to float — sometimes within 20 minutes on a clear day. During summer I was regularly pulling 25–28A through bulk for a couple of hours easily.

I know solar yield drops off a cliff in December but this feels like something's off beyond just the shorter days. Battery bank is 200Ah of lithium (Fogstar Drift cells), resting voltage around 26.1V this morning, and the Victron app is showing absorption set at 28.4V which all looks correct. The panels themselves are tilted at about 35 degrees which I've not adjusted since installation.

Has anyone else noticed this with their MPPT, or is this just a North Wales winter doing its thing? Wondering whether it's worth tilting the panels steeper for winter months — read somewhere that closer to 55–60 degrees can make a meaningful difference this time of year at our latitude. Curious what others have found.

BoatMatt | Posts: 847 | Location: Broads, Norfolk

@HollyGraham83 Totally normal for this time of year, I'm afraid! A few things worth checking though - low sun angle in winter means your panels are probably getting a fraction of their rated irradiance even on clear days. North Wales will also see a lot of diffuse light rather than direct, which really knocks efficiency back.

One thing people often overlook is panel temperature actually helps in winter - cold panels are more efficient - but it can't compensate for the reduced light hours and angle.

Worth checking your panel orientation too. Even a few degrees adjustment can make a surprising difference at this latitude during December/January. What tilt angle are you running currently? If you're at a shallow pitch you're leaving a fair bit on the table this time of year.

@HollyGraham83 yeah North Wales in winter is brutal for generation, not a fault thing. Low sun angle means your panels are rarely hitting anything close to rated output — 200W panels realistically doing maybe 60-80W peak on a grey December day is totally normal.

Worth checking your panel voltage at the MPPT input though. If it's dropping below the bulk threshold you'll just sit in float all day doing nothing useful.

Also — panel temperature actually improves Voc in cold weather, so your open circuit voltage might be higher than summer. Just the irradiance that's tanking.

My setup in [LOCATION] does similar, I just stopped stressing about the numbers and watch the Wh harvested over the day instead. The VictronConnect app daily yield graph is more useful than obsessing over instantaneous watts.

BoatClive | Posts: 1,203 | Location: Continuous Cruiser, various canals

@HollyGraham83 Worth checking your panel tilt angle as well - fixed mounts optimised for summer can lose you a surprising amount in winter when the sun barely gets above the horizon up in North Wales. Steeper tilt helps enormously this time of year. Also, have a look at your VRM or Bluetooth app at the actual panel voltage versus current figures rather than just the bulk/absorb stages - that'll tell you whether it's genuinely a controller issue or just the expected seasonal drop in irradiance. In my experience the SmartSolar 100/30 is rock solid, so I'd lean heavily towards it being environmental rather than a fault. What orientation are your panels facing? South-facing makes a massive difference in winter months compared to summer when it matters less.

FormerMechanic | Posts: 2,341 | Location: Array

@HollyGraham83 North Wales in December? You're lucky to get anything worth mentioning. I've got panels on a static in the Peaks and some days the Victron logs show bulk lasting about 4 minutes before it drops straight into float — because there's nothing left to absorb.

One thing worth checking though: battery temperature. Cold batteries dramatically change the absorption voltage threshold, and if you haven't got a Victron temp sensor fitted, the controller's just guessing. Mine was consistently under-charging until I sorted that.

Also worth exporting your history from VictronConnect and looking at the yield trends rather than live readings — puts everything in proper context rather than staring at numbers that look wrong but actually aren't.

Taffy42 | Posts: 487 | Location: Array

@HollyGraham83 snap — narrowboat on the Llangollen canal here and my Victron MPPT spent most of November convincing me it had given up entirely, turns out Welsh winter solar is just performance art rather than actual electricity generation. 🏴󠁧󠁢󠁷󠁬󠁳󠁿☁️