Which controller? Can I get away with this situation?

So here's my situation and I've been going back and forth on this for a week now.

I've got five 200W 12V panels sitting on the roof of my static, all wired in series feeding into a Victron SmartSolar 150/45. Works a treat — the calculator said I was fine and it's been running my emergency backup setup without complaint.

The problem is I've just acquired a sixth identical panel for next to nothing from a lad on Facebook Marketplace, and I cannot for the life of me figure out how to sensibly integrate it.

Here's the snag:

• Six panels in a single series string pushes my Voc well beyond what the 150/45 will tolerate safely
• Splitting into two parallel strings of three changes everything about my current/voltage profile

I know the clean answer is probably "just get a 250/60 and be done with it," but before I spend that money I want to understand whether there's a sensible workaround. Could I run the sixth panel on a separate smaller MPPT — something like a Renogy Rover or even a cheap unit — feeding the same battery bank? My bank is a 200Ah 24V Fogstar Drift setup, so there's headroom there.

Or is mixing controllers on the same bank going to cause me grief? I've read conflicting things about this and I genuinely don't know whether the controllers will fight each other or just sort themselves out.

Has anyone actually done this in practice rather than just theoretically? Particularly interested if anyone's running a hybrid controller setup on a similar-sized bank.

@AZY_Marine five 200W panels in series on a 12V system is basically telling your SmartSolar "hold my beer" whilst simultaneously setting it on fire 🔥

Panels in series stacks the voltage, so you're potentially throwing 50V+ open-circuit at a controller rated for your bank — double-check your Voc against the SmartSolar's max input voltage before anything gets toasty.

If your controller is the 100/30 or 100/50, you're flirting with the limits hard. The 100 is the max PV voltage — five 12V panels in series could easily breach that in cold UK mornings (Voc spikes when it's nippy, classic Britain moment).

Consider parallel strings instead, or if you've got the budget, step up to the 150/45 — keeps the voltage safe whilst handling your wattage properly.

@AZY_Marine the crucial thing nobody's mentioned yet — five panels in series on a 12V nominal system means your Voc could easily hit 110–115V in cold morning conditions. You absolutely need to verify your SmartSolar's input voltage ceiling before that becomes a very expensive lesson.

What model SmartSolar do you actually have? The 100/30 tops out at 100V input, which puts you in dangerous territory. Step up to the 150/35 or 150/45 and you've got proper headroom.

Also worth running the numbers through Victron's MPPT calculator (it's free, genuinely useful) — plug in your panel specs and your lowest expected ambient temperature. Here in the UK, a frosty February morning changes the calculation significantly compared to rated conditions.

Done similar on my Vivaro build and the voltage headroom issue caught me off guard initially too.

@VivaroWanderer is absolutely right and that Voc concern is the killer detail here. I went through something similar when I was setting up my garden office — had a 48V Victron SmartSolar and nearly miscalculated my cold-morning Voc by forgetting the temperature coefficient. On a bitter January morning in the UK, those figures climb nastily.

Five 200W 12V panels in series gives you a combined Voc that could genuinely fry your controller's input stage if it's spec'd for anything under ~150V absolute max. Check your panel's datasheet for Voc and apply the cold temp correction — roughly +0.3% per degree below 25°C.

Honestly, before anything else, post your panel's actual datasheet figures here and we can do the proper maths together. Takes five minutes and saves a very expensive mistake.

@AZY_Marine just to add a practical point that builds on what @VivaroWanderer and @ExFarmer90 have raised — even if your controller's absolute maximum input voltage technically covers that cold-morning Voc spike, you're potentially running very close to the limit, and Victron controllers don't respond kindly to being pushed right up to their ceiling repeatedly. Over time that stress shows.

Worth grabbing the actual spec sheet for your specific panels and running the Voc calculation at your lowest expected ambient temperature — Victron's own MPPT calculator tool on their website makes this dead simple. Plug the numbers in before assuming you're safe.

Also, what's the actual model of your SmartSolar? The 100/30, 150/35, 250/60? That matters enormously here because the first number is your hard voltage ceiling.