What size PVC conduit would you use for this 300' run?

[difranco999]

Thanks everyone for the insightful input. I will take the suggestion of being generous with size and number of conduits for future expansion and potential AC and/or low voltage runs.

I like the suggestion of eliminating the combiner box and running 5 x 10# instead of 3 x 6#.

I've updated my diagram accordingly. Full size PDF link here...

Question about this though...

Each string has a VoC of 194.5 V with 13.66 A. According to solarwiresizecalculator.com at 5% voltage drop, it suggests 8 AWG for these numbers.

Is 10 AWG sufficient because we're less concerned about voltage drop with DC runs?

But I know of no hybrid inverter or MPPT charge controller that is now high voltage (500 V DC or more) that will accept that gauge wire. Most all only accept 10-12 AWG and limit amps in to 20-30.

I double checked this on our inverter (EG4 1200XP) and see it will accept 10 AWG - 6AWG
EG4 1200xp manual p.15

 

[timselectric]

Personally I would run two #8 (+ & -) and one #10 green (EGC).
You don't need a combiner box, just a junction box.
Or disconnect, if you prefer.

 

[DougfromdaUP]

Personally I would run two #8 (+ & -) and one #10 green (EGC).
You don't need a combiner box, just a junction box.
Or disconnect, if you prefer.

Wouldn't you run two strings to take advantage of the two MPPTS he has?

Or, If only using 1 MPPT he could run one string of of all 10 panels.
VOC @-30 is 451. vmp of the string is 311, well within the inverter's requirements.

 

[timselectric]

Wouldn't you run two strings to take advantage of the two MPPTS he has?

No, I would use the full potential of one MPPT, before using another.

Or, If only using 1 MPPT he could run one string of of all 10 panels.
VOC @-30 is 451. vmp of the string is 311, well within the inverter's requirements.

This would be better, actually.
As long as temperature isn't an issue.

 

[glandpuck]

From my experience I agree with Timselectric last post above. and if you have the bucks, a larger conduit or even a second conduit. If running a second empty conduit, at least run the electrician's pull lines through it to use to pull wire in the future. And carefully mark if you can with a weather resistant cord/string on top of the conduit before you bury it so in the future you just pull up the string to know where exactly in the ground that conduit is located.

Finally, and this is just my own little Pearl, if you can manage to do it, run a 30 amp 240 AC out to near the arrays from your inverter load panel. You will be surprised how happy you will be if you ever want to add micro inverters in the future, a pump, a shed, any other structure, a pond with filters and pumps or even a heat pump hot water heater for something!

Last and not least, if you can, run a 3/4" schedule 40 water pipe and put some hose bibs along the way, say every 100 feet and with shutoff valves too. You may well want to wash off the arrays in the future or do some gardening and you are adding value to the property for a very low cost of the conduit and some glue and depth of bury not important here for water line.

 

[difranco999]

Or, If only using 1 MPPT he could run one string of of all 10 panels.
VOC @-30 is 451. vmp of the string is 311, well within the inverter's requirements.

No, I would use the full potential of one MPPT, before using another.
This would be better, actually.
As long as temperature isn't an issue.

My hesitation with running one string is future upgrade for more panels. Adding just 1 panel would put us at the DC input max (480VDC) for our inverter. (If I'm understanding things correctly.)

10 panels:


11 panels:

 

[difranco999]

deleting this post. I was misthinking things

 

[DougfromdaUP]

It wouldn’t make much sense to add one panel anyway.

I think it would make a lot of sense to add ten more now.

While you’re trenching and building a support structure, the additional costs will never be better than now. I encourage you to do some modeling with PVWatts to see if your expected solar generation fits your needs with only ten panels.

 

[timselectric]

My hesitation with running one string is future upgrade for more panels. Adding just 1 panel would put us at the DC input max (480VDC) for our inverter. (If I'm understanding things correctly.)

Pull an extra pair of conductors for the future.