Struggling to get my MPPT to play nicely with partial shade — anyone else had this bother?

So I've got two 200W panels wired in series on my shed roof (Renogy mono, bought last spring), feeding into a Victron SmartSolar 100/30. Works a cracker in full sun — hitting around 22–24A charge current no problem. But the minute that big oak at the bottom of the garden throws shade across even one corner of a panel, the whole system seems to just... give up. Drops to almost nothing rather than finding a sensible working point.

I've been reading a bit about this and I think it might be a case of the MPPT's tracking algorithm getting confused by multiple power peaks in the IV curve — apparently that's a known thing with series strings and partial shade. Some folks seem to suggest rewiring to parallel would help, though I know that changes the voltage profile significantly and I'm not sure the controller would be as happy. I'm running a 12V leisure battery bank (two 100Ah AGMs), so the panel Voc in series is around 44V open circuit.

Has anyone actually rewired from series to parallel on a similar setup and seen a real-world improvement? Or is it more a case of adding bypass diodes, looking at micro-inverters, or just accepting the loss and trimming that oak back a bit? Would love to hear from anyone who's dealt with this practically rather than just in theory — the Victron forum is a bit overwhelming if you're not an electrician.

Hey @FormerTeacher50! Classic partial shade headache, this one. Worth knowing that with panels in series, one shaded panel drags the whole string down disproportionately — it's not just half the power, it can be much worse due to how MPP tracking works across mismatched voltages.

Have you tried switching them to parallel instead? You'd halve the voltage going into the Victron but your 100/30 should handle it fine, and shading on one panel won't hammer the other nearly as badly.

Also, dig into the VictronConnect app and check your absorption/float logs — sometimes you can spot exactly when the shade hits and how badly it's affecting yield.

What direction's your shed roof facing, and roughly what time of day does the shading kick in? Might help narrow down whether repositioning one panel is even feasible. 🙂

Rewired mine to parallel after my neighbour's new shed started casting a shadow over one panel every afternoon — night and day difference, pun absolutely intended 🌑

Worth noting the Victron 100/30 handles parallel fine on that wattage, just double-check your string current doesn't exceed the 30A input limit (two 200W Renogys in parallel should be comfortably under).

Also, if rewiring feels like faff, Trina and a few others do panels with built-in bypass diodes per cell string rather than just one per panel — reduces shade impact dramatically without touching your wiring.