I have six panels facing south in 2S3P. I have three more identical panels but I only have room to put them north facing. I would like to expand to 3S3P, however I already ran the two cables to my MPPT and I don't have it in the budget to run another two cables at this point, so I can't use a separate charge controller. Would adding the new series string of 3 panels in parallel to the two south-facing series strings cause an overall drop in production or an overall increase? Would I need to get some kind of diodes to prevent backfeed into the two south facing strings?
Adding North-Facing Panels to Existing Array
- Thread starter speculant
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hwy17
Anti-Solar Enthusiast
The theory goes that it should beneficial. Diodes are not needed but fusing is needed for three strings. I don't know the details of whether 1 string needs to be fused or all three.
It's ok if 2 come on one pair of wires and the third on another pair. And it doesn't really matter which combo it is, as long as the two string pair can handle the two string amps and/or is fused appropriately.
It's ok if 2 come on one pair of wires and the third on another pair. And it doesn't really matter which combo it is, as long as the two string pair can handle the two string amps and/or is fused appropriately.
I am planning on fusing all three strings separately. When you say "it's ok if 2 come on one pair of wires and the third on another pair", are you referring to fuses or the leads to the single MPPT? Since I already ran the single pair of cables to my MPPT, all nine panels would be going to the MPPT on the same pair of cables.
hwy17
Anti-Solar Enthusiast
Oh I see I misread that part. Then you just need to ensure the single pair can handle the cumulative ISC of all the panels, OR, fuse the input appropriately if ISC exceeds it but regular currents wont.
hwy17
Anti-Solar Enthusiast
I recommend either name brand Staubli MC4 fuseholders, or a Midnite or other legit combiner.
signaturesolar.com
Just saying watch out for using generic Amazon MC4 parts.
Staubli | 20A | 1000V | In-line Fuse with MC4 Connectors
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signaturesolar.com
Just saying watch out for using generic Amazon MC4 parts.
Ok great. I already sized the pair going to the MPPT for 9 panels, as I had purchased 10 panels originally and was planning on doing 3S3P from the get-go with one panel as a spare. I just didn't check the size of my yard and the ground mounts before hand. So I'll go ahead and set up the 3 north facing panels and I'll monitor the output to make sure it's not lower than normal for a day of full sun with the six south facing panels (once we actually get a day of full sun again, may be a week or two). If it is lower, I'll diagnose from there. I just wanted to make sure as long as the north-facing panels are on a separate string, going to the same MPPT, it won't reduce the total average output vs. just the six south-facing panels.
hwy17
Anti-Solar Enthusiast
Yeah the theory goes that as long as the north facing panels can at least see the sky, that will easily bring them up to the same voltage as the other panels, so they shouldn't suck power and can only contribute anything they can get above and beyond that.
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