Mix and match Solar Sells

This makes sense, thanks!

But would you agreed that, if all panels are orientated the same direction, the Vmp will likely sit close to the Vmp of the lowest Voc?

What you said above is indeed why I like Victron’s higher amps based MPPTs more than those forcing you to put all your panels in series. You have more options. Especially when you want to combine different orientations on one MPPT.

Maybe, maybe not, it depends on the relative wattage of the strings, not the voltages.

There are many applications, some suit one thing, some suit another.
A square peg in a round hole, or a round peg in a square hole, one tries to get the best fit for the application.

Indeed. I assumed in all my argumentation that both strings are facing the same way :slight_smile:

When you are also dealing with different directions, or shading, then it could be any voltage between the two. If for example the string with the lower Vmp is entirely shaded, the MPPT will most likely pick a higher voltage (since that is an advantage to the string that’s in the sun, and no disadvantage to the side that’s shaded).

More specifically, I think people ask this question because they want to know what the performance penalty is. Well, the worst case scenario is that everything runs at the lower Vmp. So the maximum performance penalty is roughly the lower Vmp divided by the higher one.

Thank to all who contribute to this answer!
My takeaway:
worst cast, the new string will preform at the specs of the lower string.
No more 405w, i can now only get 420w.

Genade, but the solar panels are flying at the moment! Little to no stock of the popular sizes!!!


Yes, that is a good rule of thumb to use. Unless you give much more detail with regards to orientation, strings, etc. and some of the smart guys here can do some calculations. But I think if you don’t want to go that route based on the rule of thumb, you probably shouldn’t regardless of what more accurate calcs tell you.

I love to make my MPPT’s to the ceiling of their current capability.
I also try and keep them at a high current for as long as possible during the day.
I can use all the power I can get, even if the batteries are fully charged.
To this end, I began experimenting with mixing and matching arrays at different tilts and directions.
I didn’t use fancy brackets, I just worked with the roof surfaces I had.
I have four MPPT’s and 2 PV inverters ( with another 3 MPPTs in them).
I did some combining on the roof, but brought string down on separate cables. I realized very quickly that working with what an on-line solar calculator was hopeless.
Make equivalent voltage strings and actual measurements.
I reckon most people will get 60%-100% more panels on their roof without maxing out their MPPT’s
Obviously the more strings, the more MPPT’s, the more diversity of tilts and directions creates more opportunity to fine tune things.

There is a guy (I think it was in the Northen Cape) that took the East/West and all side panels to the extreme. He has panels mounted on the walls that get the very early/late sun, and then all angles in between. They were all on just a few MPPTs and he got still decent power even in heavy rain just from ambient light on the amount of extra panels. Most MPPTs will limit the current when the panels produce too much power to what they can handle. (Got to love those blue products :smiley: )

Calculator never give you all the results. They just indicate the most efficient most of the time.

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Artsolar (ZA) has just teamed up with PV giant Longi. Longi are the world leaders in bifacial PV. Apparently bifacial manufacturing is coming to South Africa soon.
I am seriously thinking of bifacial E-W PV fencing, for the very early/late sun.

That would be cool. I’m already running Artsolar arrays. I’m sure matching fencing would look great.

Just not so sure if that fence will keep the thieves from stealing your solar panels ! :thinking:

Sorry to resurrect this thread but I have a question in the same vein - as far as I can tell this would also apply to mixing Mono and Poly Panels in the same string?

Currently have 6x340W Poly Panels - VMP=37.74V and IMP=9.01A
Want to add 3x370W Mono Panels - VMP=39.6V and IMP=9.35A

Estimating the output of the 340W panels stays the same and the 370W Mono will produce 39.6Vx9.01A=356W.

The Poly panels are like hen’s teeth, very hard to find! And the Mono Panels are almost the exact same size as the old Poly and at a reasonable price. Artsolar say they are producing more 340W poly panels but haven’t given me an exact date yet or a price. And I wouldn’t mind a few extra Watts of power as these are the last three panels I can fit on my roof!

Hi JaseZA,

You are both correct and wrong on the Watt out. You have to take the MPPT into account, once you start putting different panel together the MPPT might even end up being less optimal on the original panels! But ultimately, you will not have less power that original installation!.

On that note, I am installing Module Level Optimisers on my system, this would effectively eliminate the mismatch. Will most likely post my findings on this forum a bit later (once they are in and tests have been run).

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They sometimes interfere with an MPPTs ability to find a good power point, because they tend to flatten things. I’ll wait for your results… :slight_smile:

Thanks @Rautenk - plans have actually since changed and I’m hopefully receiving Canadian Solar 365W Poly Panels at the end of the week. These are 39.8V @ 9.18A Poly panels so a little bit closer to my original spec. Will definitely post some results of how it all performs together once they’re installed - hopefully the MPPT behaves! I’m hoping for 39.8V x 9.01A = 358W output, or an relative increase of 52.5% for my string. Time will tell…

The not so long wait is over!

My first draft analysis on module optimisers for residential can be found on this link:

Module level optimisers

Last 7 days of solar - you can see where I added the new panels! They’re performing great, max in clear weather is up 1.65x (Calculated should have been 1.525 times more!)

Noticed an interesting glitch in the MPPT of my Voltronic VMiii MPPT - seems now with the mixed panels it figures out a better voltage point a bit later in the morning and suddenly produces a bit more power. Example below of my original panels being quite consistent and then the new mixed panels. Might just be the higher voltage as apposed to the mix.

Don’t think there is much I can do but thought it was interesting enough to report.

Is the MPPT’s volts sitting at 350V!? Did you put the new panels in series with the old ones or in parallel? Are you running a Victron MPPT or something else? Victron’s MPPTs are designed only to run up to 100/150/250 (or the new one 450) volts. If you don’t have the new one, I’m not sure how it is getting up to 350V… without blowing up.

New Voltronic VMiii - 500V max Voc so no issues running in series. My theoretical Voc is 420V.

Indeed. Depending on shading and other factors, the P/V curve could have multiple peaks, and if the MPPT does a rescan (which most periodically do), it may find the other peak. The change from the one to the other may also be a clearly visible event, since it is triggered by a rescan.

In applied math we called this a “local maximum”. It’s like when you climb a mountain, and you finally get over the edge just to see that there is more mountain to climb. Now imagine you couldn’t see very far, and then you know what an MPPT has to do. Sometimes it gets stuck on a small hill for half an hour, then it stops, takes a sip of water, puts on its glasses… and then it moves higher up :slight_smile:

Thanks plonkster, makes sense. I imagine it must be fun trying to figure out the best optimization in terms of how often to scan, how far to scan and not losing too much output while scanning!

Interestingly, I measure at 5 second intervals and I see no drop in PV power during the change or before it - not sure how the MPPT manages to test the best V/I position without dropping any power? Unless it’s quick enough that I don’t measure it in between the 5 seconds.