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Frustrating debate with GreenLancer for permit plans - sanity check

A

alcoolaid

New Member
Joined
Mar 15, 2021
Messages
10
Location
Boston, Massachusetts
Update: With the help here and more discussion with the rep, we figured it out! Thanks for the help everyone!

Below is a snippet of my solar permit plan notes I submitted to GreenLancer.

Solaredge SE-10000H-US

Solaredge S440 Optimizers

34x 410w panels. 18 over the house (house array), 16 over the garage (garage array).


Array Layout Readme2x9 portrait array on West facing house roof
4x4 landscape array on South facing garage roof
Three Line Diagram ReadmeGarage array:
Soladeck with fused combiner combining two strings of 8 panels. 10/2 FMC coming out from bottom of soladeck into attic space, come down wall of interior garage space (NW corner), enter PVC JB (covert to 10 awg THHN), go through PVC conduit underground to house basement. Inside basement will have PVC JB and convert back to 10/2 FMC to inverter. Might need a DC disconnect by garage? Not sure if that is necessary.

House array:
Soladeck with fused combiner combining two strings of 9 panels. 10 awg THHN in EMT across roof to edge and down along the side of the house. Enter house near meter and into inverter. Or can run two pairs of 12 awg wire and forego a combiner on the house roof (probably the cheaper option).

This is where I get very confused. Read from the bottom up. (Names have been partially redacted). Why the heck is he saying I need 8 awg cable? Is my description of how I want to do the system not clear? I'm ready to submit an email to ask for a refund so I can go with a local route. I had a friend who works for a local solar company read the information below and he doesn't understand it either?

Alexander T · 12-14-2022 3:37:52am​

You will use optimizers in this system. Max output ampacity (with 125%) is 15A*1.25=18.75A If we combite two strings into one (by parallel connection) we will have 18.75*2=37.5.

Arthur (me) · 12-13-2022 9:24:09pm​

Garage Home Run 1
String A: 8 panels x 410w = 3,280w / 400v = 8.2A
String B: 8 panels x 410w = 3,280w / 400v = 8.2A
String A + B combined in fused combiner box = 6,560w / 400v = 16.4A
Output is 10 awg wire to inverter

House Home Run 2
String C: 9 panels x 410w = 3,690w / 400v = 9.2A
String D: 9 panels x 410w = 3,690w / 400v = 9.2A
String C + D combined in fused combiner box = 7,380w / 400v = 18.45A
Output is 10 awg wire to inverter

Home run 1 and home run 2 meet at the inverter. Home run 1 and home run 2 will each carry a max of 16.4A and 18.45A respectively.

I'm not sure how you're getting 37.5A being carried on 10 awg wire? It's only 16.4A from the garage array and 18.45A from the house array? They both meet at the inverter junction block.

Alexander T · 12-13-2022 12:36:14pm​

You will use optimizers in this system. Max output ampacity (with 125%) is 15A*1.25=18.75A If we combite two strings into one (by parallel connection) we will have 18.75*2=37.5. We can not connect 18 pv panel into one string using cascade connection

Arthur (me) · 12-13-2022 5:39:25am​

Where are you getting the 37.5 amp current figure?

410w panels x 18 = 7.38 kw / 400v = 18.45 amps?

Or am I understanding something wrong.

Alexander T · 12-13-2022 3:30:49am​

If we combine two string we will have max. current 37.5A. Base ampacity for 10 awg cable is 40A and terminal amp is 35A. So we can not use 10awg for string combining. For string combining more better use 8 awg.

Arthur (me) · 12-12-2022 9:01:08pm​

Hi Alexander,

Were you able to see this note as shown below?

Garage array:
Soladeck with fused combiner combining two strings of 8 panels. 10/2 FMC coming out from bottom of soladeck into attic space, come down wall of interior garage space (NW corner), enter PVC JB (covert to 10 awg THHN), go through PVC conduit underground to house basement. Inside basement will have PVC JB and convert back to 10/2 FMC to inverter. Might need a DC disconnect by garage? Not sure if that is necessary.

House array:
Soladeck with fused combiner combining two strings of 9 panels. 10 awg THHN in EMT across roof to edge and down along the side of the house. Enter house near meter and into inverter. Or can run two pairs of 12 awg wire and forego a combiner on the house roof (probably the cheaper option?).

To summarize:
Garage - 10 awg run for 16 panels (8 series, 2 parallel)
House - 10 awg run for 18 panels (9 series, 2 parallel)

Thanks,
Arthur

Alexander T · 12-12-2022 3:09:40pm​

Hi Arthur,

we need clarify with you cable size issue. We can connect into the inverter only three strings. According to your design PS system will have 4 PV strings. It's mean we should combine two strings into one before connection into the inverter. If we combine two string we will have max. current 37.5A. Base ampacity for 10 awg cable is 40A and terminal amp is 35A. So we can not use 10awg for string combining. For string combining more better use 8 awg.

Please inform us how we should proceed.

Thank you
 
Last edited:
You're arguing array current. He's arguing potential equipment supply current and wiring requirements. If the optimizers can supply X current, they require a certain wire for that rating. If the units specify a certain minimum wire and/or fuse/breaker size for the installation, you must install them in compliance with the manufacturer's recommendations, or you violate code.

The optimizers are also likely acting as module level cut-off per NEC2017 and newer. These or similar devices are required to meet code.
 
Let's start with where the 125% of max 15 amps spec of optimizer output current comes from. I cannot find where that comes from. I highly doubt the optimizer will allow 125% of its maximum design output. If so, their spec would be 18.75 amps, not 15 amps.

Basic premise of two stage Solar Edge system is to maximize the optimizers output voltage and lower its output current (same output watts) based on the lowest illuminated unit's maximum achievable output current.

The S440 and S500 optimizers are boost only MPPT DC-DC converters. (S500B is buck-boost). Any S440 optimizer output current can never exceed PV input current because they are boost only converters. Their output can boost to higher output voltage than panel, up to max of 60vdc, but the result will always be at a lower current than lowest illuminated panel current to optimizer.

Output of boost optimizers cannot exceed PV current so if PV panel is 8.2 amps, there is no way boost only optimizer can have 18.75 amps output. Maybe on best day a little over 8.2 amps but never 18.75 amps without mirrors.
 
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Yes, where I am it's either a Solaredge system or Enphase. We require module level rapid shutdown.

My friend showed me a couple of previous plans that he recently installed. Same inverter, same optimizers. 15 365w panels per string.

That system was:
String A: 15 panels = 5,475w
String B: 15 panels = 5,475w
String C: 10 panels = 3,650w

All were wired with 10/2 FMC cable with home runs to the inverter.

Even the Solaredge design assistant tells me to run 2 strings of 8 panels and 2 strings of 9 panels. It's the best way to meet the minimum 8 panel requirement and not go over the power limit of a single string.
 
In my experience Greenlancer is really on their game. We do a few dozen systems a year and often use them to put together our SLD's. Every once in a while, they stray from what I think is right but then I dig into they are correct.

Remember they sizing to meet NEC code which results in wire much larger than we think we might need.
 
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I still have no idea how this guy is coming up with 37.5A array amperage @ 400v. All four strings combined for the whole house is only 13.9kw. And that is split up over two home runs....

I honestly think its a language barrier based on his typing skills and he doesn't understand what I want to do.
 
sunshine_eggo said:
You're arguing array current. He's arguing potential equipment supply current and wiring requirements. If the optimizers can supply X current, they require a certain wire for that rating. If the units specify a certain minimum wire and/or fuse/breaker size for the installation, you must install them in compliance with the manufacturer's recommendations, or you violate code.

The optimizers are also likely acting as module level cut-off per NEC2017 and newer. These or similar devices are required to meet code.
Click to expand...

Even if I went through his "potential" equipment supply current, it still wouldn't make sense. Solaredge says you can have up to 25 power optimizers on a single string for a single phase system. If each opto can do 440w watts, thats 11kw. Way more than what Solaredge allows per string, which is 5700w.

Solaredge says theres a minimum of 8 panels and a max of 25. It is up to the designer to read panel specs and figure out the max potential of the array not the equipment being installed. The whole reason we have fused combiner boxes is so I don't have to do multiple runs of 12/2 or 10/2 for each string. I combine them into a box with a fuse that protects each string and then the current from both is fed through a larger conductor back to the inverter.
 
I think you either need to research more, take the expert you are paying at their word, or get a refund and ask another expert for a different opinion.

Or redesign?

I just looked at my permit package. They also used the required max optimizers output of 15 amps.
If I read correctly, you requested having your two arrays broken up into two strings each.
So 15 amp "max" output x 2 parallel strings = 30 amps. NEC requires oversizing by 25% for continuous (over 3 hours?) So 30 + 25% = 37.5 amps used for calculations. Not actual current.

It's been a while since I designed my system. Why do you have 4 strings?
I thought the max string length was 25 optimizers?
Why not one string for each array?
One string of 18 and the second string of 16.
That would keep you well within the current limits you are running into.
 
400bird said:
I think you either need to research more, take the expert you are paying at their word, or get a refund and ask another expert for a different opinion.

Or redesign?

I just looked at my permit package. They also used the required max optimizers output of 15 amps.
If I read correctly, you requested having your two arrays broken up into two strings each.
So 15 amp "max" output x 2 parallel strings = 30 amps. NEC requires oversizing by 25% for continuous (over 3 hours?) So 30 + 25% = 37.5 amps used for calculations. Not actual current.

It's been a while since I designed my system. Why do you have 4 strings?
I thought the max string length was 25 optimizers?
Why not one string for each array?
One string of 18 and the second string of 16.
That would keep you well within the current limits you are running into.
Click to expand...

Thanks for the insightful response! I am doing more research here, I don't trust the expert because it is going against what Solaredge says to do and it doesn't make sense to my electrician friend who works for a solar company that does 15m in sales a year.

The max string length can be up to 25 optimizers if you have lower wattage panels, like 200w each.

The max power per string is actually 6,000w.

If I did a string of 18 panels x 410w = 7,380w. This is over 6,000w so I have to break up the string. There is a minimum of 8 panels per string so the logical thing to do is 8, 8, 9 and 9.

If I did 18 panels on one string, that is 18.45A at 400v. Too much current for the pv wire going from optimizer to optimizer.
 
400bird said:
That doesn't sound right.

What are your panels? I think I still have access to the solar edge site design tools, I'll punch it up for you if I can.
Click to expand...

Pmax 410w
Vmp 31.35
Imp 13.08
Voc 37.12
Isc 13.96

Edit: Forgot to mention I have access to the Solaredge design assistant as well. It gives me a warning that string power is exceeding max limit once I add the 16th panel on. 15 panels is fine though.
 
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Here's what the auto string came up with:
2 strings of 11
1 string of 12
1671075043085.png

You are correct, there is a max string length with those panels. It is ok at 14, when I try to add the 15th, I get this warning:
1671075112005.png

So, you are correct, there is a 6,000 watt per string limit.
Seems like you are stuck with splitting one string between each array.


I had to manually enter the specs as they don't list any panels by Solarever.
I don't think I made any typos, but let me know if you see any pertinent errors.
Those are odd panel specs. they are 54 half cut cells. They must be larger cells or somthing.
The voltage is pretty low and the current is higher than I've ever seen. Higher than my 480 watt panels, even if you add in the back side gain!
1671075298441.png
 
My garage array is about 75 feet away from the house array so when I do the auto string, it splits it into 4 strings. 2 strings of 8 panels each on the garage and 2 strings of 9 panels each on the house.

So brings me back to the original question, would you run 10 awg or 8 awg from the combiner boxes?
 

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alcoolaid said:
My garage array is about 75 feet away from the house array so when I do the auto string, it splits it into 4 strings. 2 strings of 8 panels each on the garage and 2 strings of 9 panels each on the house.

So brings me back to the original question, would you run 10 awg or 8 awg from the combiner boxes?
Click to expand...
8awg of those are the only choices.

I was looking at your layout:
It might just be my personal preference, but I really preferred wiring the arrays straight down the row/rails. Running wire up and down between rows caused extra work and time to ensure the wiring didn't hang down onto the roof surface.

alcoolaid said:

I found this reference where they talk about the 15 amp max and the 1.25 safety factor.

Although I may never see even close to 15 amp per string, they want me to have the wiring post combiner to insure it will handle 37.5 amps I guess.
Click to expand...
By they you need to point the finger at the NEC, not the one writing permits.
 
400bird said:
8awg of those are the only choices.

I was looking at your layout:
It might just be my personal preference, but I really preferred wiring the arrays straight down the row/rails. Running wire up and down between rows caused extra work and time to ensure the wiring didn't hang down onto the roof surface.


By they you need to point the finger at the NEC, not the one writing permits.
Click to expand...
Yes, the auto string made it zig zag like that but I plan on going down a row along the rail for wire management.

Glad we were able to figure out why he kept saying 15a without referencing anything clearly.

He also got back to me with a clearer explanation finally after I asked for his reference.

With this new information it will make more sense for me not to combine on the roof and run 8 awg back but instead to just run two pairs of 10/2 FMC wire since I have a bunch of that.

Thanks for the help everybody!
 
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I am looking at using GreenLancer or Santan Solar. Any input on Experiences?
 
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