Best way to wire from array to inverter

[dnbuggy]

rooftop array running about 50' into basement. 2 -12 panel arrays wired in series. Each array is 396v and 9.3amps. I am wondering the best way to run wire to the dc disconnect and inverter.

Run each string with a separate set of wires individually or combine each string together at the array and run a single set of wires down?

[ButchDeal]

what inverter are you connecting to? are you using dual MPPTs on said inverter or single MPPT?

[dnbuggy]

grid tied system. Sunny Boy 7.7

[ButchDeal]

grid tied system. Sunny Boy 7.7

That inverter has 3 MPPT inputs. Are you planning to use 2 of them?
Since each MPPT has a max current of 10 amps and your two strings have a current of 9.3 you will not be able to combine them at the roof. You will have to wire them both independently to the inverter.

[dnbuggy]

Thank you ButchDeal! I appreciate the help!

[NEOH]

Another option, if arrays are identical ...
Both strings can be connected in parallel at the roof into appropriately large wire
This allows for one pair of wires to be brought down to the Sunny Boy inverter
Connect PV wires to the MPPT Input A and parallel to MPPT Input B in parallel.
The Sunny Boy will detect this mode on power-up

[dnbuggy]

NEOH, will this parallel install be ok with the AMP rating of 10 on the Sunny Boy? I planned to use 12ga wire, would stepping up to 10ga work in this scenario?

[nwdiver]

Another option, if arrays are identical ...
Both strings can be connected in parallel at the roof into appropriately large wire
This allows for one pair of wires to be brought down to the Sunny Boy inverter
Connect PV wires to the MPPT Input A and parallel to MPPT Input B in parallel.
The Sunny Boy will detect this mode on power-up

With that configuration you lose the independence of 2 MPP channels. The array will operate more efficiently if each string can operate at its 'preferred voltage'. String level MPPT.

[NEOH]

With that configuration you lose the independence of 2 MPP channels. The array will operate more efficiently if each string can operate at its 'preferred voltage'. String level MPPT.

We should not waste our valuable time worrying about such small variances.

[NEOH]

NEOH, will this parallel install be ok with the AMP rating of 10 on the Sunny Boy? I planned to use 12ga wire, would stepping up to 10ga work in this scenario?

When MPPT Input A and MPPT Input B are connected in parallel then 10 amps + 10 amps = 20 amps total Input
Regarding wire size, there are websites that will help you calculate the % Voltage Drop over 100 feet ( = 2 x 50 feet ) with 20 amps.
What is your target % Voltage Drop?

[nwdiver]

We should not waste our valuable time worrying about such small variances.

Depending on shading it can be fairly significant. I probably lose >1kWh/day since I have 3 panels which get shade from a tree in the evening so I end up with a string of 11 in parallel with 2 strings of 14. I've got a old-school SMA inverter with only 1 MPP channel. So all 3 strings have to compromise on a lower voltage...

And if there is ever a fault in one panel like a shorted bypass diode it will lower the efficiency of the entire array. If each string is independent it won't have much of an effect at all. IMO the benefits of string level MPPT is at least worth an extra pair of wires...

[dnbuggy]

Ok, I think I am going to run two separate runs of wire. I calculated that I need 12awg wire and I found some 12/2 stranded thhn. Would it be ok to use the two 12awg green wires as my ground for the array? The main panel on the house is actually closer than my grounding rod outside. Would it be ok to ground all the way back to that panel through my disconnects and through my inverter into the breaker panel instead of to the ground rod outside? From what I read in the NEC, sharing a ground with both DC and AC is ok in this application.

[Billybob9]

As in the video of SMA 5.0 Inverter installation Grounding green wire 6awg was used. I talked to SMA and the tech there used it also. Two strings is best as Rapid shut down box has 2 outputs. I used 10awg from Shut off box to Inverter. I didn't Install the Rapid shutdown box under my last panel on the array because I believe over heating is causing the 12V relays to fail.