36 panel array stringing question with Sol-Ark 15K

[ollemar]

Hi, my second post here. I will include pictures and hopefully can explain what I'm trying to do. Inverter is located 120 ft. from array. My plan is to make strings of 6 panels in series and then parallel with branch connectors 1 and 2, 3 and 4, 5 and 6. In the manual I guess it's called "Y" connection.

Or is it possible or reasonable to run 6 individual strings to inverter?

I used Sol-Ark sizing tool and these are the exact panels.



Thank You.

 

[BentleyJ]

Forget the "Y connectors and do a proper, code compliant job. Use a combiner box for the PV strings. Midnight Solar is a good source for quality boxes and breakers.

 

[DougfromdaUP]

Four groups of 9 would also work, and give you a higher voltage for lower losses. You could certainly run each sting to the inverter and not need any combiner.
You can parallel two strings without a combiner, just join them in a box if you only want to pull four wires.

 

[ollemar]

Four groups of 9 would also work, and give you a higher voltage for lower losses. You could certainly run each sting to the inverter and not need any combiner.
You can parallel two strings without a combiner, just join them in a box if you only want to pull four wires.

Thank You, I like the idea of 4 groups of 9. Do you have any box recommendation ?

 

[prometheanfire]

4 groups of 9 would be nice but it goes over sol-arks wattage limit per mppt. 8 works though then you couldn't use the final 4 panels (Voc too low for the mppt). In this case I'd go with, in each of the three mppts, 6s2p and home run each string to the sol ark, but that's just me.

120ft away is at least 240ft round trip, the voltage loss in sol ark's calculator is 5.5% for 10ga wire if using the "Y" connector method. Their calculator is happy if you do home runs for each string (2.7% loss).

 

[Cmy]

Ask S-A the impact of nine. They allow 5% over the published 3250/string limit or 3412W. I don't know if the 9 string's extra 143W will be clipped or if it can cause future damage. Agree with higher voltage for the long run but would add four more panels so the third MPPT has a full string and an unused string for future use.

Not sure how wide your roof is, mine is wider, but I am planning landscape 4-5 panels from the ridge down, plus side up. Adjacent, minimal gap, the same number of panels plus side down. Connect the minus bottom of the left stack with the plus bottom of the right stack. You end up with that pod in series with both plus and minus inverter connections at the top. In your case, it may be better with the stack connection at the top and inverter connections at the bottom, nearer the roof's lower edge.

Approximately 11.5 ft width for the double stack, I am leaving a foot or so wide access path before the next double stack.

 

[DougfromdaUP]

I apologize- I completely missed that you have 3 mppts.

The spec sheet says "26 amp, self limiting" per MPPT, so I don't think you would do any damage, but with that many panels I think you should use all three MPPTs.

I don't think you could improve on 2 parallel strings of 6 panels each for each MPPT. You don't need fuses or a combiner to parallel two strings, so you can join them with a wire nut in the box where your conduit ends.

 

[prometheanfire]

If using 10ga wire I would avoid combining on the roof and running it, that 5+% loss is high for that length of a run.

 

[ollemar]

I emailed to Sol-Ark asking for the best solution and here's they answer:

Looks like you're already using the Solar Panel Sizing tool.
As long as there are no errors on the bottom of the results page, this should work for you.
I did notice you don't have your max ambient and min ambient temps set. Please be sure to adjust this.

I adjusted temps and it didn't change much. I'm still confused what would be the best solution. Should I just leave out 4 panels and run groups of 8 panels in series ?

 

[wdwtx2.0]

I am OCD.
I would run 6S2P per MPPT.
It divides out evenly.

 

[ollemar]

I am OCD.
I would run 6S2P per MPPT.
It divides out evenly.

So looks like this was my original plan. Just to make sure this way I run total 6 lines (plus ground) to the inverter and all 3 MPPT-s will be used.

 

[wdwtx2.0]

So looks like this was my original plan. Just to make sure this way I run total 6 lines (plus ground) to the inverter and all 3 MPPT-s will be used.

Option 1) run positive and negative from strings 1 & 2 to MPPT 1, positive and negative from strings 3 & 4 to MPPT 2, positive and negative from strings 5 & 6 to MPPT 3. This makes 6 positive, and 6 negative conductors.

Option 2) parallel strings 1-2 (array 1), 3-4 (array 2), 5-6 (array 3) at, or near the panels, and run 1 ea. positive and negative from the three arrays to the three MPPTs, for a total of 3 positive and 3 negative conductors.

As you mentioned, a properly sized ground conductor needs to accompany the PV conductors.

***My PV arrays are ground mount, so I do NOT know the rules for roof mount panels.***
I am not required to fuse my panels, but I have each string fused before my outdoor disconnect. Just in case.

 

[prometheanfire]

Option 1) run positive and negative from strings 1 & 2 to MPPT 1, positive and negative from strings 3 & 4 to MPPT 2, positive and negative from strings 5 & 6 to MPPT 3. This makes 6 positive, and 6 negative conductors.

Option 2) parallel strings 1-2 (array 1), 3-4 (array 2), 5-6 (array 3) at, or near the panels, and run 1 ea. positive and negative from the three arrays to the three MPPTs, for a total of 3 positive and 3 negative conductors.

As you mentioned, a properly sized ground conductor needs to accompany the PV conductors.

***My PV arrays are ground mount, so I do NOT know the rules for roof mount panels.***
I am not required to fuse my panels, but I have each string fused before my outdoor disconnect. Just in case.

Option 1 is the only one that he can do unless he runs something thicker than 10ga wire since the runs are so long. But this is also what I'd do.

 

[ollemar]

Option 1 is the only one that he can do unless he runs something thicker than 10ga wire since the runs are so long. But this is also what I'd do.

option 1 it is then. I really appreciate you taking your time and helping me figure this out. Do you know if i can fit 13, 10ga wires into 1 1/2 conduit ? Do you have recommendation for a combiner box for this setup?

 

[DougfromdaUP]

You can fit 37 #10 THHN in 1 1/2 IMC or EMT.

I recommend no combiner box. What would you combine in it?

 

[ollemar]

You can fit 37 #10 THHN in 1 1/2 IMC or EMT.

I recommend no combiner box. What would you combine in it?

Connection from PV wire to THHN ?

 

[DougfromdaUP]

You can make the connection in any box.

You must think about other equipment you may need- disconnect, rapid shut down, etc.

 

[kscessnadriver]

You can fit 37 #10 THHN in 1 1/2 IMC or EMT.

I recommend no combiner box. What would you combine in it?

Sure he can run that much, but with that many in a single conduit, are they going to carry the current he needs once they're de-rated properly?

 

[DougfromdaUP]

Sure he can run that much, but with that many in a single conduit, are they going to carry the current he needs once they're de-rated properly?

He’s only running twelve. I just wanted to show that he’s not exactly pushing the limits.