Mixing panels and tying in accessory line to same mppt

[MM2306]

I have 2 gopower brand 100w panels wired in series to my mppt. Specs are not easily found and I am not the one who bought them, but I think I found correct numbers online. Specs: VOC 21.0V, Vmp 17.5, Imp 5.68, Inc 6.28. Typical readings on my solar output are 130w output (29-31v at 4.2-4.5a). I have seen as high as 180w output but not typical.



So the rest is a 2 part question. I want to add permanent panels similar in specs to roof (gopower panels are $5xx per panel, I'm not spending that) and have landed on Renogy 100w. Specs on that are: VOC 22.5, Vmp 18.9, Imp 5.29, and Isc 5.75. I will wire 2 of these panels in series and then connect them in parallel to my existing two. So these feed into the input on my MPPT as parallel series. (First question, are these panels compatible enough with each other? I'm ok with losing some efficiency for the sake of saving $700)

2nd question. The exterior panel is a Zamp (reverse polarity SAE) plug that the previous owner wired into the same input slot of the MPPT as the main panels. Is it OK to wire another 2 Renogy 100w panels in series that plug into that accessory plug that go the same input as the main parallel/series I have permanently attached? Is it essentially the same as adding another parallel panel at the same junction as the other 2 series?

[bcroe]

I make sure each string I plan to parallel has the same cell count,
close enough. I have 12 panels @ 60 cells strings in parallel with
10 panels of 72 cells. Save a fortune by going to 250W to 400W
panels. good luck, Bruce Roe

[JonKeevil]

It sounds like this should work OK.

When you wire the pairs of panels in parallel, that forces the output voltage of the panels to be the same. The specs on your gopower set suggest the Voc in series should be 42V and Vmp should be 35V. They are running at 29-31 so probably not direct sun, general inefficiencies. 2 of the new panels in series have a similar output voltage range (Voc 45V, Vmp 37.8) and so when put in parallel with the gopower, the MPPT controller will hunt to find the best single voltage for the combined set.
You will probably see a bit higher voltage than you see now and it wont be ideal for either pair, but "pretty close" and will probably meet your goals.

I am not quite following the 2nd question about the exterior Zamp panels, but I think you are asking about adding panels #5 and 6 (Renogy) using an existing external Zamp plug? Assuming this plug also is wired in parallel to the MPPT giving you 3 parallel strings, that should also work with a couple caveats. 1) Whenever you combine more than 2 strings in parallel, each string should have its own fuse to keep any 2 strings from damaging a 3rd 2) check the max amperage out from the MPPT. If the actual max of a pair is 180W then 3 pair might be 540W or 45A fed into a 12V battery. If this is higher than the MPPT is rated then you wont get the full power from the 3rd set of panels when the sun is bright.
Jon Keevil

[sdold]

Hi Jon, nice first post, welcome to the forum.

[MM2306]

Thank you for the replies. Yes the 5th and 6th renogy panels will be wired as series and plug into the exterior zamp plug, however that was also rewired to go directly to the mppt where the other roof panels are being ran to. Does that make sense? Essentially the 4 panels up top are series parallel that come into the mppt as one wire, and then the exterior zamp plug is another separate wore that runs to the same mppt input.

And yes I will be sure to add a fuse to each string as you suggested. Should i use a regular fuse or a blocking diode?

[JonKeevil]

That does make sense. When all is plugged in, you have 3 pairs of series panels that are in parallel with each other.
There are a couple issues regarding breakers and fuses. Because during the day, panels are always creating power, it can be nice to be able to "turn off" the panels if you want to work with the MPPT controller for example. A dual pole DC breaker can work well for the rooftop panels and would be wired before the MPPT. Something like this. The portable panels don't need a switch because you can just unplug them.

To get to your FU question, the idea of fusing the positive lines in each string gets at the rare scenario that a panel shorted out in a way that the other 2 strings could dump power into the shorted string which could be a heating/fire risk. I would pick a fuse size like 10A which is high enough to allow one string to flow, but would blow if the amps from 2 string tried to flow backwards. There are fuse carriers in MC4 connectors like this that could work for the roof panels. You could splice in a regular 10A automotive fuse for the Zamp plug wires.

I have not used blocking diodes in this situation. I expect it could work in theory, but I think most diodes create some resistance for forward flow and drop voltage at least a little. So that would introduce some heat waste from your solar production.