pv string

[the dosser]

i have 6pv panels in 2 SP strings going to combiner box, voc 27.28 imp 10.51 200w pv
can i add two more panels in series and plug into combiner box , or do i need to add these panels to the 2 SP strings
my cc is victron 150 70
i am a rookie , thanks for the help

 

[42OhmsPA]

Please provide more details and clarity.
I'm not understanding your current strings.

Assuming Victron uses a normal naming convention and your max voc is 150v I'd rewire so you have a 4s2p setup. This would give you ~110 voc, ~ 21a; keeping the victron happy.
I'm also assuming all panels will be aimed the same direction and partial shading isn't an issue.

 

[the dosser]

they will be in the same direction, charging a 24v 660ah battery bank , i currently have 6 panels 3inS and 3in P
the panels i want to add will have partial shading in the morning for 2to 3 hours

 

[MichaelK]

they will be in the same direction, charging a 24v 660ah battery bank , i currently have 6 panels 3inS and 3in P

You need to express things more clearly. This statement is clearly incorrect. I think what you actually mean is that you have two parallel strings of 3 panels in series. You would properly write that as 3S2P.

If the original question is can you add two additional panels to each series string, then the answer is no. With a Voc of 27.28, five in series would be 27.28Voc X 5 panels = 136.4V. That looks OK, but in California, you need to expect at least freezing weather, once or twice a year. That would bump up the Voc to >152.7Voc, which is dangerous for your controller.

If the original question is can you add one panel each to the individual strings (4S2P) then the Voc at freezing would be 27.28V X 4 X 1.12x = 122.2Voc, which would be within the limits of your controller.

BTW, what kind of battery do you have? Traditional lead-acid likes charging at ~1/8th of C, so if your bank is 660Ah, then it wants 660Ah/8 = 82.5 charging amps. With only six 200W panels, while charging at ~25V, that bank is only seeing (200W X 6 panels)/25V = 48A. If you de-rate your output like I do to 85%, that is really only 40-41A.

Since your controller has the capability to handle 70A, then what you actually need is (70A X 25Vcharging)/85% = 2058W. Possibly get an additional six panels instead of just two, and wire them 3S4P. What might work well for you is virtual tracking. Keep two arrays pointed South, and the other two pointed either East/Southeast and West/Southwest.