Mixing panel wattages on a single MPPT — is it actually worth it?

So I've got two 200W panels already mounted on my tiny house roof (Renogy mono, bought last year) and I've just come across a decent deal on a single 320W panel. My Victron SmartSolar 100/30 has the headroom for the extra input, and I'm wondering whether it makes sense to string them all together or if I'm just asking for trouble.

From what I've read, the MPPT will track down to the lowest-performing panel's characteristics, which worries me a bit. Would the 320W essentially be "held back" by the two 200W panels, or does the controller handle that more intelligently than I'm giving it credit for?

Has anyone actually done this in practice rather than just theory? Curious whether the real-world output figures end up being disappointing compared to running them as separate arrays on separate controllers. I know Victron kit is generally solid but I don't want to waste the potential of that 320W panel if stringing them together kills the efficiency.

Also worth noting — my roof orientation isn't perfect, slight east-west bias, so the panels aren't always hitting peak simultaneously anyway. Does that change the calculus at all?

@PaddyGibson ran almost exactly this experiment on my narrowboat last summer. Had two mismatched Renogy panels feeding my SmartSolar 100/20 and the short answer is — it works, but the MPPT will only pull to the lowest common denominator panel's characteristics if they're wired in parallel.

What actually saved me was wiring the odd panel on a separate string input. Your 100/30 only has one pair of PV terminals though, so you'd need a combiner with bypass diodes, or honestly just consider a second small MPPT for the 320W alone.

The maths rarely lies: three panels theoretically giving you 720W but actually delivering 580W because of mismatch losses isn't the bargain it looks on paper.

What's your roof orientation — all panels facing the same direction? That changes the equation considerably.

The critical thing people overlook here is that the MPPT will pull everything down to the lowest-performing string's characteristics under partial mismatch conditions. With your 320W panel having a different Vmp than those 200W Renogys, you're essentially handicapping the larger panel constantly.

What I'd actually suggest — check the Vmp figures on the datasheets carefully. If that 320W panel runs significantly higher Vmp (often 32-36V range versus the 200W panels), you might be better off running the 320W solo on your 100/30 and finding a separate cheap PWM controller for the two 200W panels in parallel.

@DaiHenderson's narrowboat experience is worth heeding here. The Victron SmartSolar app will show you harvesting losses if you monitor it properly over a few weeks — the data doesn't lie.

@PanelEwan makes a fair point but worth adding — it's not just about wattage mismatch, it's about Vmp differences too. If those Renogy 200W panels and the 320W have similar voltage characteristics you'll lose less than you think.

Done something similar on my narrowboat — ran a mismatched pair through my SmartSolar for about a season. Wasn't catastrophic, just not optimal. Ended up putting the odd panel on a separate cheap MPPT and honestly the improvement was noticeable.

For a tiny house where space and budget matter, two separate controllers might be the cleaner solution. A basic 20A unit for the 320W doesn't have to cost much. Keeps each string operating at its own sweet spot rather than compromising both.

Check the Vmp specs before deciding — if they're close, mixing might be fine short-term.

@DaiBennett makes a good point about Vmp — that's really the crux of it. I'd add from a practical standpoint: check whether those 200W Renogy panels are wired in series or parallel before you do anything else, @PaddyGibson.

In my experience (ran a mixed setup for about eighteen months on our smallholding), parallel wiring with mismatched panels tends to behave more predictably day-to-day, especially on cloudy mornings which is rather a lot of our weather here! Series can amplify the mismatch problems @PanelEwan mentioned quite significantly.

Your 100/30 Victron will cope, but I'd honestly spend ten minutes with the Victron MPPT calculator first to check your combined string voltages don't creep too high in cold weather. Easy to overlook that in the excitement of a bargain panel! 😄

@PaddyGibson one thing worth considering that hasn't been mentioned yet — have a look at whether your 100/30's 30A output limit becomes the bottleneck before your panel mismatch does. Three panels totalling 720W into a 12V battery bank would theoretically demand around 60A, so you'd be leaving a fair chunk of potential harvest on the table regardless of the mixing issue. If you're on 24V it's more manageable at ~30A. Check your actual bank voltage first.

Also, have you considered simply putting the 320W on a separate cheap PWM or second MPPT controller? A basic 20A unit costs very little and you'd get cleaner performance from both setups rather than compromising everything into one controller. Sometimes the tidy single-controller solution isn't actually the most efficient one in practice.