Running a Victron SmartSolar 100/30 with a 400W array (2x 200W Renogy panels in series, Voc ~45V each so ~90V combined) feeding a 200Ah Fogstar Drift LiFePO4 in my garden office. Summer was flawless — pulling 25-28A on a good day, bulk/absorb/float cycling perfectly. Now we're into proper grey UK winter and something odd is happening.
On overcast days the controller seems to be outputting almost nothing despite the panel voltage sitting at a reasonable 60-70V (measured via the VictronConnect app). Current out is dropping to 1-3A when I'd expect maybe 8-10A given the irradiance. The MPPT tracking algorithm should be hunting for the maximum power point regardless of conditions — that's the whole point of MPPT over PWM. Battery is at 80% SOC so it's not a case of absorption/float throttling the charge.
Wondering if this is a temperature compensation issue, a firmware quirk, or something about low-irradiance MPPT tracking that I'm missing. I've read vague references to some MPPT controllers struggling to track efficiently when the power curve is very flat (which it apparently is in diffuse light) but I've never seen it properly explained. Has anyone actually measured their harvest in winter and compared it against what the irradiance should theoretically be giving them?
