Anyone else finding their Victron MPPT undersized after adding more panels?

So I started the season with a 100/30 Victron SmartSolar on my van and it's been brilliant — no complaints. But I've just bolted on a third 200W panel (two Renogy 200W flexi panels already on the roof, now a rigid 200W on a tiltable mount at the rear) giving me 600W total. The 100/30 is rated to handle up to 1000W on a 24V system but I'm only running 12V, so realistically it's capped at around 360W useful output. I'm leaving watts on the table every sunny afternoon.

I'm torn between upgrading to a 100/50 (which would push me to about 600W capacity at 12V) or just rewiring the three panels into a 2S+1P or full series config to bump the array voltage up and stick with the 30A controller. Problem is two of the panels are flexi with a Voc of 24.3V each — putting two in series gives me 48.6V Voc which should still be within the 100V input limit, but it feels tight once you factor in cold morning temperatures.

Has anyone done the sums on cold-weather Voc correction for flexi panels specifically? I'm in the north of England so we do get proper cold snaps. Not sure if the temperature coefficients on cheaper flexi panels are reliable enough to trust for this calculation.

@DuctTapeDave94 worth checking your actual array Voc against the 100V input ceiling before you connect that third panel — three 200W Renogy flexi panels in series will almost certainly blow past the 100V limit and fry the MPPT, especially on a cold morning when Voc climbs.

If they're wired in parallel instead, you're probably fine on voltage but your combined Isc will likely exceed the 30A charge current limit, so you're leaving harvest on the table.

Realistically you're looking at stepping up to a 150/45 or 150/70 SmartSolar. The 150V input headroom is the real win — gives you proper series wiring options and much better efficiency at lower light. Victron's MPPT sizing calculator on their website will confirm your specific numbers. It's a genuine upgrade rather than a workaround.

@QMC_Camper has already flagged the critical bit — Voc headroom — so I won't repeat that.

What I will add: three 200W panels in parallel keeps your Voc identical to a single panel, so if you're wiring them that way you're fine on the 100V ceiling. Your actual bottleneck becomes the 30A charge current limit. At 12V nominal, 600W theoretical maximum is 50A — you're potentially clipping heavily in peak sun.

On my system I hit exactly this ceiling and upgraded to the 150/45 SmartSolar, which gave me breathing room without the cost jump of the 150/70. Worth costing up — usually around £160–180 from Bimble Solar or VoltaicSystems.

Also worth noting: flexi panels routinely underperform their rated wattage, so real-world losses might mean clipping is less severe than the maths suggests. Run a few days of data through VictronConnect's history tab before spending anything.

Great points already made by @QMC_Camper and @BarryWood. One thing worth adding — even if your Voc stays safely under 100V, your 100/30 is capped at 30A output to the battery. With 600W of panels, on a good day you could theoretically be pushing towards 40A+ depending on your battery voltage, so you'd be leaving real charging capacity on the table. Whether that actually matters depends on your usage patterns — if your battery's usually topped up by midday anyway, the 30A ceiling might never bite you in practice. But if you're running heavy loads or have a larger battery bank, it might be worth considering stepping up to a 100/50 at some point. They're not hugely expensive secondhand on eBay. Worth doing the sums on your actual daily consumption first before spending anything though.

Been down this exact rabbit hole on my narrowboat last spring — started with a tidy little array and then "just one more panel" turned into a whole afternoon of head-scratching.

What nobody's mentioned yet: string configuration matters as much as the controller rating itself. If those three Renogy panels are wired in parallel, your Voc stays manageable but your current shoots up — potentially past the 30A ceiling on that 100/30. At 600W theoretical peak you're already nudging it hard before efficiency losses are even considered.

Ran the same maths before I upgraded to a 150/35 and honestly the jump wasn't as expensive as I feared. Victron's sizing tool on their website is worth five minutes of your time before you commit either way.

@DuctTapeDave94 one thing nobody's touched on yet — check your actual clipping losses before assuming you need to upsize.

With three 200W panels you're nominally at 600W but your 100/30 caps output at roughly 430W (30A × ~14.4V absorption). That gap sounds painful but in UK conditions your panels will rarely hit STC anyway — cloud, angle, temperature all knock real-world output down significantly.

Run a week's worth of data through VRM if you've got the dongle; look for sustained periods where charge current is pinned solid at 30A. If that's only happening for 45 mins either side of solar noon on clear days, your losses are minimal and upgrading the MPPT is hard to justify financially.

If you are clipping for hours daily, a 150/45 or 150/60 SmartSolar is the logical step — keeps your existing cable runs and battery bank wiring intact.

@Taffy29 makes a fair point actually — clipping on a van is often less dramatic than you'd think cos you're rarely sat in perfect south-facing sun all day anyway.

That said, 600W into a 30A controller is pushing it. At 12V system you're theoretically pulling 50A peak — controller will just clip hard and you'll lose a fair chunk on good days.

Personally went through this last summer, ended up swapping to a 100/50 and it's been worth every penny. Kept all my existing wiring too which was the main win.

If budget's tight, the 75/15 range won't cut it obviously, but Victron's 100/50 is solid and second hand ones pop up on eBay regularly for decent money.

@DuctTapeDave94 worth double-checking your panel VOC figures before anything else — three 200W flexi panels in series could push you dangerously close to or over the 100V input limit on that controller, especially on a cold morning. That's the bit that worries me more than the current side of things. If they're wired parallel you're probably fine on voltage but you'll definitely be saturating the 30A limit. @Taffy29 and @BatterySam are right that clipping isn't always catastrophic in practice, but a van moving around changes the calculation quite a bit compared to a static install.

@DuctTapeDave94 went through almost exactly this when I expanded the cabin array — had a 100/30 sweating away and kept convincing myself I'd "sort it later." Eventually swapped to a 150/45 and the difference was immediately obvious, particularly on those overcast autumn mornings when the panels are doing 70% and every watt genuinely matters for topping the batteries before dark.

One thing worth factoring in given your EV charging ambitions — if you're ever planning to scale up properly, buying the right controller once is considerably cheaper than two purchases eighteen months apart. Ask me how I know.