EMT conduit question for multiple strings

[Jdcarrol]

Is it ok to run the wires of multiple PV strings in the same EMT conduit to the inverter? trying to think if I need 3 sets of conduit for 3 PV strings or if I can try to have them all in one conduit.

Also, for the EG418KPV, PV input 1 can take 2 series but I hear they have to be identical. My system will be roof mounted with all the same type/brand/model of PV module. Both the east and west facing sides of the roof with have 10 panels in a series. Can I bring these two series into the PV1 input because they are identical in quantity and type or not so because they are facing different directions?

 

[DIYrich]

There is a limit on how many wires you can put in a conduit. Based on size of wire and size of conduit.

 

[Hedges]

Yes.

There are conduit fill tables, but physically getting wires in can be difficult, especially around bends, so you will probably fit fewer.

There is derating for more than 3 current carrying conductors. For 3 strings, 6 conductors (not counting ground), 80% of wire ampacity. But you won't be near that anyway.

Yes, you can parallel two identical strings of different orientation. It should work great unless one gets heavy partial shading, like 5 shaded and 5 getting sun on west side, all 10 getting sun on the east.

What is Isc and Imp of the panel? What are the current ratings of PV1 input? Likely the two strings will produce about 1.6x as much current as a singe string, give or take depending on angle between them. Try a little trig.

 

[zanydroid]

I think you can fit 6 conductors plus one EGC in 3/4” EMT. And #10 should be fine after derating with a 1P config. 2P would be marginal / illegal IMO and require #8 if paralleling at the roof..

Yes you can 2P into the first MPPT but why not split it across all three MPPTs or try it both ways?

 

[Jdcarrol]

I think you can fit 6 conductors plus one EGC in 3/4” EMT. And #10 should be fine after derating with a 1P config. 2P would be marginal / illegal IMO and require #8 if paralleling at the roof..

Yes you can 2P into the first MPPT but why not split it across all three MPPTs or try it both ways?

the 18PVK has 3 inputs (2 can parallel in the 1st input), I will have a total of 3 strings and planning for a 4th one in the near future, so I'd like to use the 1st PV input as parallel if possible.

 

[Hedges]

(2 can parallel in the 1st input)

Two strings can be paralleled to the first input? Or the first two inputs can be connected in parallel to handle higher PV current?

One could always parallel strings externally, then feed one pair of wires to the hybrid.

How many MPPT does the 18kPV have? How many PV inputs does it have?

What are the voltage, current, wattage ratings of the MPPT inputs? Of your panels?

 

[zanydroid]

The first input is specc'd for 2x of the other two. I don't remember if it's exactly 2x but it has higher max current it can draw, and higher Isc.

 

[zanydroid]

the 18PVK has 3 inputs (2 can parallel in the 1st input), I will have a total of 3 strings and planning for a 4th one in the near future, so I'd like to use the 1st PV input as parallel if possible.

OK if you plan to reuse the conduit for 4th string make sure to check if wires need to be oversized. Since going from 6 to 8 CCC triggers the next stage of derate. 80% -> 70% IIRC.

Probably there is enough margin in #10 but do the math.

 

[Hedges]

Or, parallel the strings before conduit, only 6 current carrying conductors. Just need to size the wire correctly, not derate further.

 

[zanydroid]

Parallel before will definitely require upsizing the parallel conductor.

#10 calculations:

40A *.8 / 1.56 = 20.5A

So you need panels of 10.25A Isc which is not common these days

 

[Hedges]

Different orientations would reduce peak current.
Even if NEC doesn't approve of engineering calculations.

If derated ampacity exceeded, choice is 8 awg for this circuit, or just use 4 pairs of 10 awg which have plenty of ampacity despite derating.

Using separate wires for each string leaves flexibility for inverter changes.

 

[Jdcarrol]

Thanks y’all for the information.

 

[jjww]

Warning!! i used the PV cable from Signature Solar and it was larger in diameter than standard PV wire (if there is such a thing!) and 6 plus ground would not physically fit let alone pull into a 1"EMT. luckily my 1st pull box in attic was only 6" into attic which allowed me to drop back to #10 THHN for the 6 wire pull back to the inverter.

 

[Jdcarrol]

Warning!! i used the PV cable from Signature Solar and it was larger in diameter than standard PV wire (if there is such a thing!) and 6 plus ground would not physically fit let alone pull into a 1"EMT. luckily my 1st pull box in attic was only 6" into attic which allowed me to drop back to #10 THHN for the 6 wire pull back to the inverter.

Thanks, my PV wire is from Santan Solar, it's all good stuff, but much more robust/big than THHN and I plan to transition to THHN to save myself a lot of headache

 

[Jdcarrol]

Yes.

There are conduit fill tables, but physically getting wires in can be difficult, especially around bends, so you will probably fit fewer.

There is derating for more than 3 current carrying conductors. For 3 strings, 6 conductors (not counting ground), 80% of wire ampacity. But you won't be near that anyway.

Yes, you can parallel two identical strings of different orientation. It should work great unless one gets heavy partial shading, like 5 shaded and 5 getting sun on west side, all 10 getting sun on the east.

What is Isc and Imp of the panel? What are the current ratings of PV1 input? Likely the two strings will produce about 1.6x as much current as a singe string, give or take depending on angle between them. Try a little trig.

This is what I just got back from signature solar on the question, “Panels on MPPT 1 (input 1 and 2) must be equal in module count, type, orientation, and shading. If they unequal, you will see a drastic decrease in power output as the entire array will drop to produce the same as the lowest producing panel.” Thoughts on that? They make it sound like 10 panels facing east on one string and 10 panels facing west in a string should not be put in parallel in PV input 1

 

[Hedges]

No problem at all having one string of 10 panels facing East and one string of 10 panels facing West, connected in parallel and fed to single MPPT.
So long as Voc is within limits, and current is within limits.

SMA and other manufacturers had also said "same orientation". Later, they ran a field test because installers wanted to do otherwise (and maybe had.) Those of us who think, and looked at PV panel I/V curves, already knew it was OK. SMA found 2% lower power production than with separate MPPT.

Unfortunately, they took down their white paper and I hadn't downloaded a copy.

In series, yes, current is limited to lowest producing panel. So all need to be same orientation.
In parallel, voltages are pulled to the same. Which is not far from Vmp.

Now if 5 panels of one string are shaded, then performance would be dragged down.