Parallel vs series strings on a 24V system — worth the extra complexity?

Currently mid-build on my Ducato and trying to nail down the final panel configuration before the roof brackets go on permanently. Running a Victron SmartSolar MPPT 100/30 and planning four 175W panels (Renogy monos, Voc 24.3V each, Isc 9.47A). The question is whether to wire two 2S strings in parallel (2S2P) or just run all four in series — except obviously four in series would blow past the 100V input limit, so that's out. So realistically I'm looking at 2S2P giving me ~48.6V open circuit and ~19A combined.

The 2S2P setup should sit comfortably within the 100/30's 100V and 30A limits, but I'm a bit wary of mismatched strings causing one to drag the other down if I get partial shading from roof vents or a Webasto fitting. I know the MPPT will just chase one compromise voltage across both strings rather than optimising each independently. A Victron SmartSolar 150/35 would give me the headroom to run a higher-voltage single string, but that's another £60-80 and I'd need different panels.

Has anyone run 2S2P on a 100/30 and actually found shading mismatch to be a meaningful real-world problem, or is it mostly theoretical hand-wringing? Also wondering if bypass diodes in the panels do enough to mitigate it in practice. Concrete data points from actual installs would be far more useful than the usual forum speculation.

@DucatoSolar had almost this exact dilemma when I was sorting the roof layout on my tiny house build last spring. Ended up going 2S2P with my panels feeding a Victron SmartSolar 150/35 and honestly the higher Voc string gave me noticeably better harvest on those gloomy Midlands mornings when voltage matters far more than current.

The thing nobody mentions — series strings handle partial shading from roof vents or aerial mounts much worse than parallel. If your Ducato roof is anything like mine, there's always something casting a shadow somewhere.

Worth checking your 100/30's max input voltage carefully against your 4-panel Voc in series. On a cold January morning those numbers creep up fast.

What's your panel Voc figure?

@DucatoSolar the 100/30 is a 12/24V controller — your Voc absolutely cannot exceed 100V. Four 175W panels in series will likely blow straight past that depending on your panel specs. Check the cold-temperature Voc, not the STC figure, and add about 15-20% for winter mornings.

Two strings of two in series-parallel gives you headroom and better partial-shade handling, which matters on a Ducato roofline with aerial mounts, cab peaks etc getting in the way.

That said, wiring complexity is real. I've got a similar arrangement on mine and the combiner fusing adds faff. If your panels have identical specs (crucial — don't mix batches) it's manageable.

Post your actual panel Voc and we can run the numbers properly rather than guessing.

Good shout from @SOC_Nerd on watching that Voc ceiling. One thing worth adding — don't just check your panel's standard Voc, check the cold weather Voc. On a crisp winter morning those figures can jump considerably, and if you're ever parked somewhere like the Scottish Highlands in January, you'll be glad you accounted for it. Most panel datasheets include a temperature coefficient figure; run the numbers for around -10°C to be safe.

For a 24V system with the 100/30, two parallel strings of two panels in series is usually the sweet spot — keeps you well inside the voltage limits whilst giving you a bit of redundancy if one string has shading issues. What's your typical parking situation like? Heavy tree cover changes the calculus a fair bit.