Mixing panel wattages on a single MPPT — anyone actually done this?

Planning my tiny house roof layout and I've ended up with a bit of an awkward situation. I've got two 200W Renogy panels left over from my van build, and I'm looking at adding two new 400W panels (probably Victron or similar) to beef up the system. The obvious question is whether I can run all four through one controller or if I'm asking for trouble.

I know the theory — the MPPT will pull everything down to the lowest-performing panel in a string — but I'm less clear on how bad that actually is in practice. Would it make more sense to wire the two 200W panels in series as one "string" and the 400W pair as another, then feed both into a Victron SmartSolar with dual MPPT inputs?

Has anyone actually tested the efficiency loss when mixing wattages like this? I've seen conflicting stuff online and most of it seems to be American forums where the kit and roof sizes are completely different. Wondering if it's just cleaner to sell the 200W panels and start fresh with four matched 400W units.

Done exactly this on my shepherd's hut — two older 175W panels paired with a single 200W on one Victron SmartSolar. Not ideal, I know, but it's what I had.

The main thing I'd flag is that your string voltage and current needs to match up sensibly. The MPPT will track to the lowest common denominator in a parallel string, so mismatched Vmp can cost you efficiency.

What I ended up doing:

• Kept the mismatched panels on separate MPPTs once I realised the losses
• The Victron app made it really obvious something was off

If you're committed to a single controller, wiring them in parallel rather than series tends to handle wattage differences better, as long as Voc stays within limits.

What MPPT are you planning to use? The headroom on the controller spec matters a lot here.

Hey @PaddyGibson, done something similar on my allotment setup — mismatched panels on a single Victron MPPT. The key thing people don't mention enough is to make sure your string Voc doesn't exceed the controller's input limit when it's cold. British winters can push Voc noticeably higher than the panel spec suggests, so factor in a temperature correction.

Also worth checking whether you're planning series or parallel strings — with different wattage panels, parallel often makes more sense to avoid the lower-performing panels dragging down the whole string.

What MPPT are you eyeing up? If it's got decent headroom on the input voltage, you'll likely be fine. The Victron SmartSolars are brilliant for this because you can monitor exactly what's happening via the app and spot any issues early. Don't let the mismatch put you off — plenty of us are running exactly this kind of hodgepodge setup successfully!

Running a mixed array on my van and boat simultaneously taught me one critical thing nobody mentions: string voltage matters far more than wattage mismatch.

Your 200W and 400W panels are almost certainly different Voc/Vmp values. Wire them in parallel (not series) and the MPPT will track the lower-voltage panel's characteristics, which hammers efficiency on your 400W units.

What I'd actually do in your position — put the two 400W panels as one string into your MPPT, then run the 200W pair as a separate string into a second MPPT input if your controller supports dual inputs (Victron SmartSolar 150/35 does this nicely).

Check the datasheets for Vmp on all four panels before committing to any configuration. The wattage difference is almost a red herring — it's the voltage curves that'll bite you.

Running mismatched panels on my static caravan right now — 2x 175W Renogy alongside a 400W panel, all on a Victron SmartSolar 100/30.

The bit nobody mentions: string voltage matters more than wattage. Your 200W and 400W panels almost certainly have different Voc figures. Wire panels in parallel if the voltages don't match closely, not series — otherwise the lower-voltage panel drags everything down to its level like a lazy colleague on a group project.

Check the Isc of each panel too. Your MPPT needs to handle the combined short-circuit current with some headroom.

@PaddyGibson what are the actual spec sheets showing for Voc and Vmp on both panel types? That'll tell you whether series strings are even an option here, or whether you're going parallel-only regardless.

Great thread, @PaddyGibson. One thing worth adding to what's already been said — pay close attention to the Isc (short circuit current) differences between your 200W and 400W panels before wiring anything in parallel. Mismatched currents can mean your smaller panels effectively become a bottleneck, dragging down the output of the larger ones.

Personally I'd lean towards keeping them in separate strings if your MPPT has dual inputs — the Victron SmartSolar 100/30 and above handle this really well and can track each string's MPP independently, which genuinely makes a measurable difference in real-world conditions rather than just on paper.

What MPPT are you actually considering? That'll change the advice quite a bit. Some controllers handle the mismatch far more gracefully than others.