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Connecting panels

David Botha

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Hi. I have an Axpert 5kwa inverter with 1 pylontech 3.5kw battery and 4 canadian 320w panels. The 4 panels are in 2 strings of 2 each combined on the roof with 2 y-shaped MC4 connectors. I have bought 2 more panels (330w) with a combiner box with place for 6 strings of panels. Should I separate the 4 existing panels into 2 strings or can I keep them combined? 

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I am assuming you want to add the 2 new panels as a string. Strings are series and when you join them that join is parallel. When you join batteries or panels in parallel the volts(V) stay the same while the current(A) double. 

So if each string of 2 panels are 80V and give 10A, the current 2 strings combined will give you still 80V, but 20A. If you add a 3rd string you still get 80V, but now with 30A.

Now for parallel connection it does not matter if you combine them all in the same place, or if 2 are on the roof and the new one a bit later, as long as it is still connected in parallel (All the positive cables from each string connected on the same cable and all the negative cables connected on the same cable). So you don't need to split those.

However just make sure your cable can handle the current (Amps) for all those strings. 4mm2 for instance can handle 48A while 2.5mm2 only 36A and you want some margin to that.

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Yes you can. 

You have something like this on the left and you want to add the set on the right. If all the red cables is connected somewhere and all the black cables connected, it is still in parallel. The connection does not need to be at the same spot.


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Just to make sure I understand you correctly: what I currently have is four panels that are connected in serie 2X2 strings and then joined with y-connectors. Does that make it a parallel connection? How do you choose between parallel or serie connections? What are the pros and cons?



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David, a string is panels that are connected in series. So if you have 2 panels in a string it means that the first panel's negative is plugged into the second panel's positive. The string then has a positive connector (the one from the first panel) and a negative connector (the one from the second panel)

Now is you have a second set like that, then you have 2 strings of 2 panels each. 

To connect these 2 strings to each other in parallel you need to connect the positive connections of both strings together and the same with the negative connectors.
A Y connector is used for this, or just joining them by other means. This is also notated as 2s2p (2x series, 2x parallel), or in some cases 2x2.

So I assumed you were talking about 2s2p because you said:

5 hours ago, David Botha said:

2 strings of 2 each

But that might not have been what you meant?

The easy way to know is to count the amount of Y connectors in use. If you count 2 Y connectors that would be 2s2p. If you count 4 Y connectors that would be 4 in parallel (4p)

If you do have 2s2p you can add 2 more panels to make it 2s3p by joining these 2 new panels in series as described above and then using 2 more Y connectors to the existing set.
NB! You just need to make sure the cable that is in use will handle the extra current. Also your PV fuses will need to be able this new current.

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