Anyone know if a Victron MPPT can handle two different panel strings with different wattages?

Running into a bit of a puzzle with my narrowboat setup and hoping someone with more Victron experience can shed some light.

I've currently got a 100/30 SmartSolar feeding from two 175W panels wired in series, which has been solid for the past couple of years. The issue is I've managed to get hold of a decent 260W panel second-hand — Renogy mono, good nick — and I want to add it to the array rather than let it sit unused.

My understanding is that mixing panels with different wattages can work provided the voltage characteristics are compatible, but I'm not entirely sure how the MPPT handles tracking when the panels have mismatched Vmp values. Will it just settle on a compromise tracking point and underperform both strings, or does it cope reasonably well?

A few specific questions:

• Would it be better to run the 260W panel as its own parallel string, or integrate it into the existing series string (accepting that Voc/Vmp figures won't match cleanly)?
• Is there a risk of the higher-wattage panel actually pulling the tracking point away from the optimal for the 175W panels significantly?
• Does the 100/30's charge algorithm handle this gracefully, or am I looking at meaningful efficiency losses?

Worth noting my bank is 200Ah of Fogstar lithium, so I'm reasonably keen to squeeze decent charge performance out of whatever I can manage, particularly through the winter months when I'm relying on it more heavily for emergency backup purposes.

Any real-world experience with mixed-wattage arrays on Victron kit would be genuinely useful here.

@MeadowDweller doing something similar at my cabin actually. The 100/30 will handle mixed wattage strings fine electrically, but the real gotcha is if you wire them in parallel — the lower-performing panel (or the one in partial shade) will drag down the whole string's output.

Worth checking your Voc figures carefully too. The "100" in 100/30 is your max input voltage — mix the wrong panels in series and you could exceed that on a cold morning when Voc spikes.

What are the specs on the second set of panels you're thinking of adding? If the Vmp values are reasonably close, parallel usually works well enough in practice. Victron's MPPT tracking is fairly robust at finding the best operating point even with slight mismatches.

@MeadowDweller worth noting the 100/30 has a 100V Voc limit — that's the thing that'll bite you before mismatched wattages do. Different wattage panels are generally fine if the Voc and Vmp are reasonably close, otherwise the lower-spec string drags performance down.

I ran a mixed setup on my tiny house for about a year — two 200W Renogy alongside a single 160W panel I had spare. Worked, but the 160W was the weak link.

If your panels have significantly different Vmp values you'd honestly be better off splitting them across separate inputs or using a second controller. Fogstar have decent budget options if cost is a concern.

What are the actual Voc/Vmp specs on both sets of panels? That matters more than the wattage difference really.

Hey @MeadowDweller, good question! Just to add to what @LiFePO4Fan mentioned about the Voc limit — make sure you check your combined open circuit voltage of both strings if you're wiring them in series, ideally accounting for cold temperature conditions (Voc rises as temperature drops, which matters on a narrowboat on a frosty morning!).

If you're wiring the different-wattage panels in parallel instead, Voc stays the same as a single string but you'll want matching Vmp values to avoid the higher-voltage string effectively throttling the other. Victron's documentation is actually pretty decent on this — worth a read through their MPPT sizing calculator too. What are the specs on the new panels you're thinking of adding?

Yeah @MeadowDweller mixed wattage strings are fine on a Victron MPPT — it just pulls to the lower string's characteristics effectively. The bigger thing nobody's mentioned yet: mismatched strings in parallel means the higher-wattage panels get dragged down to match the lower ones. You lose some efficiency but it works.

If you're wiring them in series though, mismatched current ratings cause more grief than mismatched wattage — the lower-current panel becomes the bottleneck.

Had a similar bodge on my garden office setup with a Renogy 200W alongside a 160W for a while. Worked, just wasn't optimal.

Honestly Victron's MPPT Connect app will show you exactly what harvest you're getting — easy to spot if you're losing meaningful output vs running dedicated strings.