Anyone else noticed MPPT efficiency drops on cold mornings before the panels warm up?

Been running a Victron SmartSolar 100/30 paired with two 200W panels (wired in series, so about 44Voc each = ~88V combined) feeding into a 100Ah lithium on my van. Generally love the setup, does exactly what it says on the tin.

Thing is, on cold mornings — we're talking 2–5°C here in South Wales lately — I'm seeing the controller take ages to properly "wake up" and start pulling decent amps. Panel voltage looks fine on the VictronConnect app, sometimes sitting at 91–93V open circuit which makes sense for the cold, but the actual charging current stays weirdly low (like 2–3A) for the first 20–30 minutes even when there's decent sun. After that it ramps up normally and hits 15–16A no problem.

Not sure if this is just normal MPPT behaviour at low temps, a BMS issue on the battery side throttling things initially, or something else entirely. The battery was at about 60% SOC those mornings so it's not like it was nearly full. Anyone else seen this with Victron kit specifically, or had similar with other MPPT controllers? Curious whether tweaking any settings in the app might help.

@GaryLewis87 yes, absolutely see this on my shepherd's hut setup. Cold panels actually push higher Voc than rated — worth double-checking your combined open circuit doesn't creep too close to the 100V input limit on that controller when it's genuinely cold. At -10°C you can see Voc rise 10-15% above the datasheet figure.

The efficiency dip itself is partly the MPPT algorithm hunting for the true power peak — lithium's acceptance behaviour at low state of charge in cold temperatures makes that harder.

Are you using the VictronConnect app to log the yield data? Worth pulling up the History tab and comparing morning harvest curves against midday. Mine showed a clear 20-30 minute settling period before tracking stabilised properly.

@GaryLewis87 worth noting this isn't really an efficiency drop — the MPPT is actually working harder to find the true MPP when the IV curve is shifting around as panels warm up. What you might be seeing is the controller briefly hunting.

On my narrowboat I've got panels in series too and on frosty mornings the Voc can spike noticeably above the rated figure — cold temps push voltage up, which is why you always derate your string voltage calculations for UK winter conditions. The 100/30 handles it fine but the SmartSolar app will show you exactly what's happening if you check the live data during that morning warm-up period.

If you're seeing actual power loss rather than just the controller taking a moment to lock on, it might be worth checking your cable runs for any resistance issues.

@BoatEwan makes a fair point on the terminology. What I actually notice on cold mornings is the MPPT spending a few minutes "hunting" — you can see it in the Victron app, the power graph looks a bit jagged before it settles.

On my ground mount setup I've got a Victron SmartSolar 150/35 and it's most pronounced when the battery is already fairly full. The controller's sweep algorithm seems to struggle slightly when both the panel curve and the battery acceptance are changing simultaneously.

Worth checking your absorption voltage too — if it's set a touch low for cold conditions the whole morning can feel sluggish. Fogstar cells in particular seem to respond well once everything warms up and proper bulk charging kicks in.

Not really a fault, just how MPPT works in real-world conditions rather than the spec sheet.

@RetiredEngineer86 on my narrowboat the Victron spends those few minutes "finding itself" like a teenager on a gap year, meanwhile I'm sat there with cold hands waiting for the kettle to boil — the irony of off-grid life is real.

Ha, @MariaJones that description is absolutely spot on 😄

Worth adding for @GaryLewis87 — with panels in series at those voltages, you might actually notice this effect more pronounced than folks running parallel setups. Cold temperatures push Voc higher (roughly -0.3% per °C on most silicon panels), so on a crisp winter morning your combined open-circuit could be nudging 95-96V before things settle. The SmartSolar 100/30 handles it fine since you've got headroom, but that wider voltage sweep gives the algorithm more ground to cover during its initial hunt.

Worth a glance at your VictronConnect history — the "yield" graph on cold clear mornings often shows that characteristic shallow ramp before it locks in properly. Completely normal behaviour, not a fault. If it's taking longer than 5-10 minutes though, might be worth checking your battery absorption voltage settings.

@MariaJones that gap year analogy is genuinely perfect.

One thing nobody's mentioned yet: cold panels produce higher Voc, sometimes significantly so. With @GaryLewis87's series string that's potentially pushing 95-96V on a crisp Welsh morning — still within the 100V input ceiling of the SmartSolar 100/30, but worth monitoring via the VictronConnect app rather than just assuming your summer calculations hold year-round.

The temperature coefficient on most poly/mono panels runs around -0.3% to -0.35% per °C for Voc. Drop 20°C below STC test conditions and you're adding several volts to your string. I nearly caught myself out with exactly this on a similar series configuration before I started logging properly through VRM portal.

Short version: the MPPT efficiency is fine — the voltage headroom is what deserves your attention in winter.

@Taffy29 is right about the higher Voc in cold temps — worth flagging that with 88V combined at STC, you could briefly spike closer to 95-96V on a frosty morning. SmartSolar 100/30 cuts off at 100V so you're fine, but it's tighter than people realise. Had a similar setup on my static and actually measured 94.2V one January morning with a multimeter. Not dangerous but worth knowing before anyone thinks "I'll just add another panel."

Good point from @Pylontech_Wizard there — worth actually checking your cold morning Voc with a multimeter before assuming the MPPT is misbehaving. If those panels are creeping toward or past 100V on a frosty morning, your controller's input ceiling becomes the real story, not efficiency drift. The SmartSolar 100/30 will clip or shut down rather than damage itself, which can look exactly like poor efficiency from the outside. A cheap temperature logger overnight might tell you more than the Victron app alone, @GaryLewis87.