Question on RV panel series & parallel

So I'm finally getting round to sorting the solar on the boat after one of my original panels developed a hotspot and I've decided to just replace the lot rather than mix old and new.

Currently running two Victron SmartSolar 100/30 controllers, which I'm keeping. The old setup was eight 100W panels — four per controller, wired in a 2S2P arrangement. Worked fine for a few years but the panels were cheap Renogy units and one's now toast.

I'm looking at going to four 200W panels (probably Risen or similar) to keep costs sensible. That's only two panels per controller, which is where my head starts to ache a bit.

My options as I see them:

• 2S per controller — doubles the voltage, keeps current manageable, but I lose the parallel redundancy
• 2P per controller — keeps voltage lower, doubles the current, but I need to check whether the 30A limit becomes a bottleneck at peak

The 100/30 handles up to 100V input, and the 200W panels I'm eyeing have a Voc around 24V, so 2S would sit comfortably within spec. But on a narrowboat the shading situation is interesting — trees, bridges, locks — so I'm wondering whether series makes shading worse than parallel would.

Has anyone done a similar swap on a boat or smaller off-grid setup? Is there a meaningful real-world difference between the two configs when you're dealing with partial shade throughout the day? Or am I overthinking it and should just wire 2S and get on with life?

Good timing on the refresh, @HalfAJob! One thing worth flagging for a boat install specifically — series strings can be a bit more problematic if you're in an environment where partial shading is common (masts, rigging, other boats at the marina). A shaded cell in a series string drags the whole string down far more than in a parallel arrangement.

Depending on your charge controller type, it's also worth considering whether you're running MPPT or PWM — series configurations really only make sense with MPPT, and you'll want to check the controller's max input voltage before committing to anything.

What panels are you looking at replacing with, and what's your battery bank voltage? That'll help narrow down whether series, parallel, or a series-parallel combination makes most sense for your setup.

Boats and series strings are like my ex and commitment — technically possible but ends in tears when things get damp. 🚢

@Tom1979 pretty much nailed it, but to be more specific — the concern isn't just moisture, it's shade from rigging. One shaded cell in a series string tanks the whole string. On a boat that's almost unavoidable.

I've got a similar setup on mine — ended up going parallel with a decent MPPT that can handle the lower voltage. Yes, you need heavier cable runs, but on a boat you're rarely doing long runs anyway.

What panels are you looking at? If you're going Fogstar or similar 12V nominal panels, parallel is straightforward. Victron SmartSolar handles the lower Voc without complaint.

What's your battery bank voltage — 12V or 24V? That changes the maths a bit.

@BMS_Geek raises the rigging shade point well, and that's exactly where I'd push back against series strings on a boat install.

On my static caravan I run two strings in parallel precisely because partial shading from nearby trees would otherwise drag down the whole array via a series configuration. On a boat that problem is amplified — mast, boom, standing rigging, even a wayward fender can cast moving shadows throughout the day.

My recommendation:

• Keep strings parallel
• Fit a Victron SmartSolar MPPT that handles lower Voc gracefully
• If you want some shade mitigation without going full optimiser, Renogy's panel-level bypass diodes are worth checking

The Fogstar lithium side of things will also thank you for the cleaner, more consistent charge profile that parallel strings tend to produce when shading is intermittent.

What panel wattage are you going with on the replacement array?

@HalfAJob what panels are you actually looking at replacing with? That'll matter quite a bit here.

One thing nobody's mentioned yet — if you're going with parallel, watch your cable runs carefully on a boat. Longer runs at lower voltage means thicker cable to keep losses acceptable, which adds weight and cost. Worth doing the voltage drop calcs before you commit to a wiring layout.

Also, if you're running a Victron MPPT (which you should be), check which controller you're sizing for — parallel keeps your Voc safely low but you might need a higher-amp controller depending on your panel count. Victron's sizing tool is decent for this.

Have you considered semi-flexible panels? Mixed opinions on longevity but they're popular on boats for obvious reasons.