Is this the best way to add more PV to my system?

[pvdude]

Wife & I finished placing the 12 PV panels today!


Next week I’ll go pick up the batteries, and we can turn this thing on for the first time.

There is room for 4 more panels on the frame, so we could do 16.
Is the following the correct way to proceed to add 4 more REC 365AA?

Currently have 12 panels in series, about 524vdc @ 9.5A
The charge controller is a Schneider Conext MPPT 100A 600VDC.
It operates from 230 to 550vdc.

So I can’t put any more in series, or voltage will be too high for the CC.

Adding 4 panels, I could split into two strings of 8 series.
That would provide two series strings of 352vdc, 19A, connected in parallel.
5840 watts.

Is this the best way to use 16 of these panels?
Thanks,
pvdude

 

[Alphacarina]

I don't see any other way - But your 200 feet of #10 feed wire would probably need to be upgraded to #8 or maybe even larger wire

Don

 

[pvdude]

Thanks, good point about the cable.
I ran 4 #10 in the conduit, onlu used two for the existing connection.
Could double up w/ the spares.
Not sure what AWG number two #10 connected together would yield.

 

[Alphacarina]

Sure - #10 seems to be adequate for 9.5 amps with your string of 12 panels, so adding four more and doubling the current would also be fine with another pair of #10 feed wires - Just paralleling a pair of #10's effectively equals a #7 wire

Don

 

[Forbisher]

Thanks, good point about the cable.
I ran 4 #10 in the conduit, onlu used two for the existing connection.
Could double up w/ the spares.
Not sure what AWG number two #10 connected together would yield.

352Voc
19A
200 feet one way
Is 2.16% voltage drop on 10AWG

Click on link to see results and change inputs.

Voltage Drop Calculator

This free voltage drop calculator estimates the voltage drop of an electrical circuit based on the wire size, distance, and anticipated load current.

www.calculator.net

 

[Alphacarina]

That drops to about 1% with a #7 cable

Don

 

[Forbisher]

That drops to about 1% with a #7 cable

Calculator has a double cable input.

Using two 10 AWG is 1.08% voltage drop.
352Voc
19A
200 feet one way.

Voltage Drop Calculator

This free voltage drop calculator estimates the voltage drop of an electrical circuit based on the wire size, distance, and anticipated load current.

www.calculator.net

 

[Alphacarina]

1.08% is exactly the same number it gives for a #7 wire - Which I guess confirms that a pair of #10's paralleled does equal a single #7

Don

 

[Forbisher]

There is room for 4 more panels on the frame, so we could do 16.
Is the following the correct way to proceed to add 4 more REC 365AA?
View attachment 48303
Currently have 12 panels in series, about 524vdc @ 9.5A
The charge controller is a Schneider Conext MPPT 100A 600VDC.
It operates from 230 to 550vdc.

So I can’t put any more in series, or voltage will be too high for the CC.

Adding 4 panels, I could split into two strings of 8 series.
That would provide two series strings of 352vdc, 19A, connected in parallel.
5840 watts.

Is this the best way to use 16 of these panels?
Thanks,
pvdude

How cold does it get at your location?
Temps lower than 77°F raise the Voc.
528V x 1.1 temp compensation for about 32°F is 580V which is well over the 550V limit.

 

[svetz]

You might find this thread of interest too: Figuring out how many panels in series and parallel based on your MPPT

 

[pvdude]

Thanks for all the tips, links and comments!
Yes, it does get to 32 degrees here once or twice a year, just before sunrise.
I had thought to simply disconnect the PV array on those nights.
But at my age, I have about 3 functioning brain cells remaining, and two of them are always
looking for where I left my glasses.
So I would forget to disconnect and the CC would not like it.

Seems like the most simple and expedient solution is to add 4 panels, configure two series strings of 8, and parallel those.

It occurred to me that I can just treat each string as an independent 8S, thus only putting about 350vdc @ 9A on each pair of #10 wires.

I can combine them at the charge controller, instead of the Midnite solar, to obtain parallel.

Just have to split the connections in the midnite solar combiner (un-combiner, in this case), add another SPD 600, done.

 

[schmism]

1.08% is exactly the same number it gives for a #7 wire - Which I guess confirms that a pair of #10's paralleled does equal a single #7

Don

You can mostly consider the calculation between single wires and multiple as a function of their total cross sectional area.

so a single #10awg = 5.26mm^2 *2 = 10.5 which happens to be almost the same as the 10.6 of a #7 awg.

AWG - American Wire Gauge Converting Chart

American Wire Gauge (AWG) vs. cross sectional area converter.

www.engineeringtoolbox.com