Close but not exact PV strings...is this close enough ?

[Cannonsville69]

Have 2s2p strings of two 2x410w panels in series (Four 410w panels) . I just got three $50 , 310w panels and three
of them in series voltage would be close but not real close . The existing 2s2p array of 410w panels is on 100 ft
of 8ga copper into a 150/70 Victron into three 48v-100ah eg4 , so alot of CC headroom still. Thinking about adding a
series string of three of these 310w panels in parallel with the 2s2p array of 410w panels. Not sure if the small loss
is worth buying another CC ... I'm not too concerned if i lose some efficiency doing this . I have inline mc4 diodes i
could add at the end of the string . I'm thinking i will lose maybe 10% of the 3x310w/930w but it's still at least another
700w if i do it . Anyone else do something like this or have a similar array set up ? Please share your thoughts.
Another CC is also not out of the question as i already have two extra sets of 8ga in my 4 inch conduit ...
but i'd like to either confirm or invalidate my thinking on adding a series string of 3 310w to my two 410w .
(On a side note, this small 410x2 2s2p array is one of three other, larger independent arrays i have on
different CC's , two on a 48v system and one on my older 12v ) (weekend fishing/hunting off grid cabin)

Please comment only if you have actually tried this or run anything similar ... comments about how the sky
is falling, how my cabin will burn down, all my CC's will fry , NEC or "Dont do it" with no explanation don't help...
I think i know the reasons why i could do this and the reasons against it ...i'd like to confirm both.

Thanks in advance all !

 

[Mattb4]

Unless I am adding wrong it would appear that you have a 22vDC difference from the 2S 410w panels you are intending to parallel the 3s 310w panels with. That is beyond anything I have ever tried. I certainly would be interested in your results if you go ahead with it. My personal feeling is that by doing this your MPPT controller will bridge the gap and raise the Array's Vmp point to somewhere between the mismatched strings. your Arrays Voc will be dragged down to the Voc of the 410w panels. If I am correct you will see a higher than theoretical watt gain than calculated using the Imp of the lowest panel. Panels are a bit of a different thing than standard DC supplies since they are neither battery or AC rectified.

This of course is assuming that you simply don't burn things up.

 

[Cannonsville69]

Unless I am adding wrong it would appear that you have a 22vDC difference from the 2S 410w panels you are intending to parallel the 3s 310w panels with. That is beyond anything I have ever tried. I certainly would be interested in your results if you go ahead with it. My personal feeling is that by doing this your MPPT controller will bridge the gap and raise the Array's Vmp point to somewhere between the mismatched strings. your Arrays Voc will be dragged down to the Voc of the 410w panels. If I am correct you will see a higher than theoretical watt gain than calculated using the Imp of the lowest panel. Panels are a bit of a different thing than standard DC supplies since they are neither battery or AC rectified.

This of course is assuming that you simply don't burn things up.

Thanks for the helpful input . I have these inline diodes that are integrated into an MC4 connector. I was thinking put them at the end of the strings ... I have them on another array which has panels facing southeast and identical panels facing south. They are not fighting or pumping current into each other and i'm getting more than i thought i would from the two arrays ... What im thinking with these 2x410 and 3x310 is similar to what you posted except that i think i will get 10-15% less than the sum wattage of all panels . I don't see it burning things up . I don't see any way it would
do that, especially with the inline diodes ...but, that is why im asking on here . Sometimes you don't know what ya don't know. Tnx Sir appreciate it !

 

[Solar Guppy]

As your diagram indicates having 3 in series parallel with 2 in series will have poor results as you will have close to a 22V difference in VMP between them

Your images of the panel label show 9.93 and 9.96 amps @ vmp for the two panel types, so putting them all in series would be the best solution, but only if you mppt charge controller is ok with 5 panels in series

When running in series, it is the amps that matter, not so much the voltage as in all in series you will have the best harvest as amps match.

 

[Cannonsville69]

As your diagram indicates having 3 in series parallel with 2 in series will have poor results as you will have close to a 22V difference in VMP between them

Your images of the panel label show 9.93 and 9.96 amps @ vmp for the two panel types, so putting them all in series would be the best solution, but only if you mppt charge controller is ok with 5 panels in series

When running in series, it is the amps that matter, not so much the voltage as in all in series you will have the best harvest as amps match.

21v difference in Voc, not necessarily Vmp ...i don't know what the real world Vmp would actually be until i connected each series string in parellel with each other . Not concerned about best harvest/max efficiency as it's just 3 cheap panels. More concerned if it will work as drawn ...even at 25% loss on the three 310w it would still be worth it to me... but much more loss than that and i'd probably just get another CC ...do you see any chance for damage even with inline diodes ? if so, please explain ...again i'd rather just add some watts instead of buy another CC and the work/time reconfiguring things . I'd buy another CC if i had six or 9 of the new panels or if this is really bad . I have this 150/70 sitting here using less than half of it's capacity . Thanks bud, appreciate it !

 

[Solar Guppy]

No harm in just connecting as drawn and then you can see first hand what the mppt charger can do with it ... or not. Blocking diode would be a required ( just on the 2 panel string ) as the voltage of the 3 panel string would be back feeding the 2 panel string otherwise.

 

[Cannonsville69]

No harm in just connecting as drawn and then you can see first hand what the mppt charger can do with it ... or not. Blocking diode would be a required ( just on the 2 panel string ) as the voltage of the 3 panel string would be back feeding the 2 panel string otherwise.

Thanks bud . This is what i was thinking . I appreciate it