Mixing panel wattages on the same MPPT — actually fine or am I asking for trouble?

Finally got round to expanding my garden office array. Started with 2x 200W Renogy panels last year, and I've now picked up a couple of second-hand 175W panels (different brand, slightly different Voc) to bolt onto the roof as well. Plan is to run all four into my Victron SmartSolar 100/30.

The Voc on the Renogy 200s is around 24.3V and the 175s are coming in at 23.1V. Series is out because the roof layout won't allow the runs, so I'm looking at wiring them all in parallel. In parallel the Voc mismatch shouldn't be an issue as far as I understand — the MPPT just sees the combined current and a single voltage.

Has anyone actually done this long-term though? My concern is whether the stronger panels end up effectively pulling current backwards through the weaker ones on partial shading days, and whether I should bother with individual bypass/blocking diodes on each string. The Victron app will tell me overall production but I won't have string-level visibility unless I add shunt monitoring separately.

@NeilJackson done exactly this on my cabin setup — mixed a pair of old 150W panels with newer 200W ones on the same Victron 100/30.

The main thing I learnt the hard way: mismatched Voc values matter more than wattage. If they're wired in series the lower Voc panel becomes the limiting factor for the whole string. Worth checking whether parallel wiring makes more sense for your specific voltage figures.

Also worth knowing the MPPT will just find the best compromise across the array — you won't damage anything, you'll just potentially leave some capacity on the table.

What are the actual Voc figures on those second-hand panels? That'd help figure out the best configuration rather than guessing.

@NeilJackson the key thing people miss is that mismatched panels in series is where you get stung — the whole string is limited by the weakest panel's current. If your 175W and 200W panels have different Isc values, you're leaving power on the table.

Safer approach: put the matched pairs in their own parallel strings. Your Victron MPPT handles multiple strings fine as long as you stay within Voc limits (check the combined open-circuit voltage doesn't exceed the controller's max input — critical on cold mornings when Voc spikes).

On my narrowboat I'm running 3 different panel sizes across two strings into a Victron 100/50 — works a treat once you've done the voltage maths properly. Grab the spec sheets for both panels and compare Vmp and Imp before committing to a wiring config.