Anyone else struggling to get accurate readings from their MPPT controller in cold weather?

I've got a Victron SmartSolar 100/30 running two 200W panels on my static shed setup in the Peak District, and I've noticed over the last few weeks that the readings on the VictronConnect app seem all over the place compared to what I'd expect. Temperatures have been dropping to around -3°C overnight and I'm wondering if that's throwing things off, or whether it's something else entirely.

What's confusing me most is that on a clear, cold morning I'm sometimes seeing voltage spikes up to around 43V on the array before the controller properly wakes up and starts pulling it down. The panels are rated Voc 45V at STC so I know I'm not massively over spec, but it still makes me nervous. Is this normal behaviour for crystalline panels in the cold, or should I be looking at the controller settings?

Has anyone done temperature compensation on their battery charging profiles for winter? I've got a 200Ah lithium (a BudgetLiFePO4 branded one, nothing fancy) and I'm not sure whether the SmartSolar handles that automatically or if I need to tweak the absorption and float voltages manually for the colder months. Would really appreciate any input from people running similar setups in northern climates.

HollyGraham83 | 47 posts

@Megan1960 Yes! Had the exact same issue last winter with my SmartSolar 75/15. Worth checking your battery temperature sensor is properly connected if you've got one fitted - the controller adjusts its charge voltage based on temperature, so without accurate temp data it can look like the readings are going haywire when actually it's just compensating (or failing to compensate) correctly.

Also, cold panels actually produce higher voltage than rated, which can catch people off guard first thing in the morning. Perfectly normal behaviour but looks odd on the app if you're not expecting it.

What readings specifically are looking off to you - voltage, current, or state of charge? Makes a difference to where the problem might be. Peak District winters are brutal so it's worth ruling out the simple stuff first! 🙂

VoltPaddy | 134 posts

@Megan1960 Quick question — are the voltage readings going wonky or is it mainly the wattage/current figures that look off? Asking because cold temps actually affect these differently.

Cold panels can genuinely push open-circuit voltage higher than your STC spec (roughly +0.3-0.4% per °C drop below 25°C), so if your panels are rated 45V Voc and it's -5°C up in the Peak District, you could theoretically be seeing ~50V+ briefly at dawn. That's not a faulty reading — that's physics being awkward.

What's your actual Voc rating on those panels? Worth double-checking you're not accidentally nudging the 100V input limit on that 100/30 before the array warms up. Been caught out myself on the boat with exactly this nonsense in January.

CamperRachel | 89 posts

@Megan1960 Worth bearing in mind that cold temperatures actually boost panel voltage — Voc rises as temps drop, so if your panels are rated at say 24V open circuit at STC (25°C), you could genuinely be seeing higher voltage on a crisp Peak District morning than the spec sheet suggests. That's normal and actually a good thing for charging!

Where things get trickier is the wattage figures — if your battery is already fairly full and the controller is tapering the charge, the power readings will look misleadingly low even with strong irradiance.

What does your battery state of charge look like when you're seeing the odd readings? And are you running lithium or lead-acid? Battery chemistry makes a real difference to how the MPPT behaves in cold conditions. That might help narrow down whether it's genuinely a sensor issue or just the system doing its job.