Does having a East & South array affect my Grid Inverters efficiency?

[KenInNC]

Hi, First time post and I am struggling with who to believe on the internet about some of the solar facts I come across for my current 8.1kW roof panel install. I have 24 panels but my South roof can only hold 15- SunPower (SPR-P17-340-COM) 340w panels and the West roof will hold 9 panels of the same type. These are commercial panels that are placed in landscape mode and have parallel circuitry which limits shading loss to the shaded part only. This will be going to a RePlus (Renesola) 8000kW grid tie power inverter which between the 24 panels and the inverter so far have cost only $3,000. I thought everything was going well in my plans then I saw a uTube video where the India sounding girl mentioned that sending power from two different direction arrays could cause issues or less energy production due to the different voltages coming into the inverter. I am not using any Micro Inverters or Optimizers. My South facing roof does not get any shading and the East one would only in early winter sunlight and that wouldn't be for very long. I guess I am a bit confused with the whole voltage in series to the inverter because if I did the 15 South panels that would be VMP 42.5v x 15 = 637.5v @ Imp 8.00A x 15 = 120A and the East 9 Panels (if lucky) could produce VMP 42.5v x 9 = 382v @ Imp 8.00A x 9 = 72A.

So help me please ... what is the theory for incoming power to the inverter? Where is this going to go wrong for the panels or the inverter? Recommendations? I don't have a combiner box as of yet or the quick disconnect for DC and AC as I am trying to buy once and not have to do this by trial and error. I hope I didn't leave too much out and that this is understandable.

Maybe I have my math wrong but looking at that doesn't make sense if the wires with the MC4 connectors are say 12-10awg then how could I even connect 15 panels together if they have 120 amps of power at peak production going through them? Shaking my head here ... I plan on using a combiner box with a heavy 8awg or what ever the books say I need for safety.
Thank you

[Mike90250]

You can chose to listen to the do-dahs on fool-tube, or get advice here, from real world folks. Maybe Butch can chime in with his split array results.

[KenInNC]

Thank you Mike. Thats why I turned to this forum ... I hope I can learn and grow my solar knowledge here. I did read the stickies and I have gone through a bit of the forum looking for a similar question but I didn't find any answers yet. Personally I would think that the Grid Tie Inverters were designed for variable DC input as that is how the solar panels work but I just want to do it the right way the first time. I have lots of questions but I figured one per topic is best. Thank you again

[ButchDeal]

I am not sure which inverter you are using? Does it have one mppt or more? Is it rated for over 600v input? Seems strange.
i would think yiu would need to have three strings of equal size so 15 on one and 9 on the other will not work well , unless inverter has multiple inputs.
You are going to need a combiner for a string system.

[bcroe]

What is going on, you have already built a system before resolving these problems? If you
want to parallel strings, each string must have the same MPPT voltage. Here that means
the same number of panels. Here you might have 3 strings of 7 panels each, and the panels
in each string are exposed to the same sun or shading. 8 per string, if you can manage 16
on one side.

The current from a series string is NOT multiplied by the number of panels (the voltage is).

And the open circuit voltage must never exceed the inverter input voltage limit. Typical
open circuit voltage is 25% higher than MPPT voltage, and increases with cold. Bruce Roe

[ButchDeal]

It looks like the RePlus is a micro inverter which doesn't fit with the rest of the question.
I don't see an 8kW inverter by Renesola but they do have a GW8000-DT which is 8.3kW and dual MPPT. Is this the one one you have?
It does have an MPPT voltage range of 200-850V but not a US version (not sure where you hare though).

If this is the inverter then it will work fine (someplace were that voltage is ok by permit on residential). and you would use both MPPTs, one per azimuth.

http://www.renesola.com/file/Global/product/pdf/Inverter%20and%20Accessory.pdf

[KenInNC]

Thank you Butch and Bruce. I am on the iPad and will put better details tomorrow as I have the Replus 8000 TLB-US which is the USA name from Renesola. I got a guy in CA who bought all of the Replus stock before they left to go back to China due to the Trump tariffs. He is selling very reasonable. Anyways... Yes this is fly by the seat to a point. The info is on Renesola website for this model but the link is on the computer. Specs:


Input Data
Max DC 8300w
Mac DC voltage 360v
Start voltage 360v
DC rated voltage 379v@240Vac
PV voltage range 345-600v @ 240Vac
MPP voltage range 345-480v @ 240Vac
Max input current 30A
Max input current per string 16A

Output Data
Nominal AC output power 8000w
Max. Output current 38A@240v
AC nominal voltage/range 240V / 211~264V
Power Factor 1
THDI <3%
AC connection two phase

Efficiency
Max Efficiency 97.8%
CEC Efficiency 97%
MPPT Efficiency 99.5%

Protection
DC - reverse polarity yes
DC insulation measure yes
AC short circuit protection yes
Output over protection-varistor yes

i did get a WebBox communication data logger and a wifi interface as well

4 PV+ and 4 PV-
DC switch is 50A/600v
AFCI module is 50A
AC outputs L1/L2/N/PE. #8-#4AWG

[KenInNC]

Forgot DC input wires 12-8AWG. There were 208V specs but I am 240V. I have the open circuit voltage and will post that in the morning. Thank you gentlemen!

[Mike90250]

Your input data looks odd. Could you recheck and look for typos ?

Input Data
Max DC 8300w
> Mac DC voltage 360v
> Start voltage 360v
DC rated voltage 379v@240Vac
PV voltage range 345-600v @ 240Vac
MPP voltage range 345-480v @ 240Vac
Max input current 30A
Max input current per string 16A

[KenInNC]

You are correct Mike. Good eye ... I couldn't copy and paste so I keyed it incorrectly with the iPad.

Max DC voltage 600v
Start Voltage 360v

I can't seem to find the catalog of the US items since they are shutting that side down. I only have the unit, manual and whats on the box label for specs.

[KenInNC]

Inverter spec sheet

[KenInNC]

The original panel layout plan. Big array is South facing and smaller array is East facing.

[KenInNC]

Overall property layout. Showing garage to the West of the house. I am open for suggestions for roof mounted PV. Thank you.

[ButchDeal]

Your MPPT range is 345V to 480V. Not sure of your temperature variance but your PV modules have a VMP of 42.5 so you are going to want much shorter strings than you suggested.
It would have to be modeled but somewhere around strings of 9.
The problem is that you have 24 modules which is NOT divisible by 9. You could do 3 strings of 8 but the problem there is that you have 9 pv modules on one roof facing East.
The whole setup would be better with an inverter that has two MPPTs and down right trivial with optimizers. If you can fit one more PV module south facing to have two strings south and one east it could work (marginally).

[KenInNC]

Thank you Butch and sorry for not responding fast but my iPhone wouldn't let me chime in while I was a bit down in the weather for the weekend.

So I guess the thing that screws this up even with three strings of 8 where 16 (string A & B) are on the South and 8 (string C) on the East (hypothetical) ... due to the variance of the voltage of A + B coming in as a parallel set normally being higher producing through out the day when compared to C which could have the same voltage but would produce less voltage as it gets shaded from the sun going to the west a hour or so after the noon sun, this would make my single MPPT Inverter suffer once the C string started to drop in voltage? Is this similar to when a panel in a string gets shaded and the others don't the power of the string gets reduced to the weakest link?

This may sound silly, but if I were to design a Arduino board that could turn off the C string's connection to the MPPT at the point when it will hurt the voltage going to the MPPT from all three strings would that do better? My original goal was a 10kW system (that is the limit the power company will allow here per meter box). I purchased 30 panels because with shipping it was better to do it now than later (also if I broke one or one went bad I had a replacement if not all were used).

So in a perfect world ... all strings go to the MPPT Inverter with the same incoming voltage produced from the PV cell strings?

I am attaching the PV data sheets as there are several specs and I am not positive which one is temperature variance. I see Power Temp Coef, Voltage Temp. Coef, Current Temp Coef and Temperature for operating conditions.

I really do not want to do a ground mount due to my backyard's limited space. But I may rethink this for a possible new C string location. Did I mention I live in Wilmington NC where Florence smacked us directly? This is why I prefer roof mounts. My garage to the left of the house in the backyard photos has a 60' long roof which could act as a C sting but it is steeper than the house (6/12+).

I have heard others mentions somewhere in the forum of the Solar for Dummy's kind of book but I didn't think it would get that deep to the point of the questions I may ask. I have tried to learn as much as I could over the past three months and yes I have bought items before knowing what was the best but it was because of the deals I got.