DIY 11.7kw ground based grid tied system questions?

SteinVT

New Member
Hello, first time poster here.
I am in the early stages of my ground based build. The system will consist of 32 Adani Bifacial 365w panels, Enphase micro converters and Enphase combiner box with IQ envoy. I am working with a local distributer who has limited knowledge of the Enphase units. I am located in Vermont where there are minimal hoops that need to be jumped through regarding permitting.

No problems with the mechanical racking, but I am starting to realize how little I know about the actual interconnection of the Enphase inverters. After spending a number of hours watching Enphase training videos, here is what I have come up with.

I will need at least three branch circuits to handle the 32 inverters. Each of these branches can be feed into the Combiner/Envoy. Using center taps in the branches it should look something like this. The array is 2x16P.
PanelBranchLayout.JPG
The combiner box is weatherproof and so initial thought was to hang it off the superstructure. But the array is maybe 150 feet from my house and doubt it will have sufficient WIFI to connect to the internet.

Options that I can find;
1) Use a Q Aggregator to combine the branches and then run a homerun to the Combiner which I would locate in the garage.
2) Run three 20A Homerun branch circuits all the way to the garage.
3) Leave the combiner/envoy on the array and add an Enphase power line carrier pair to get the data to the router

Any and all comments welcome. I am enjoying getting a peak into this world and I am so happy I came across this forum. It's great to find so much knowledge and experience in one place. -Thanks Mark
 

MPRanger

Beefield, GA 30461
Your initial gut feeling to hang the combiner off the superstructure is a good one. Too bad you didn’t pull a cat6 line too. It’s never too late to wire networking, but there are directional antenna as long as you have 120V at both sides.
 

SteinVT

New Member
Thanks for the reply. It's not too late as I haven't laid the conduit yet.

So no problem running a data line along with the power conductors? - Mark
 

MPRanger

Beefield, GA 30461
Use Cat 6 shielded. If you can put it in a separate conduit. Same hole (ditch).you won’t be sorry. I recommend a 15A power one too. You’ll find use in monitoring equipment, data or camera sometimes.
 

SteinVT

New Member
Doing more reading, I think I want to add usage monitoring coils to the Envoy system which will necessitate it living in the garage. I think the easiest way to do this is using the Q Aggregator, basically a junction box, and then a home run. Then communications is not a problem. Thanks for the reply - Mark
 

newbostonconst

Solar Addict
I have a similar system and used a outdoor rated circuit breaker box (~$30) as a combiner box. Ran each enphase branch circuit to its own breaker and trenched a main home run to my main panel. Using a circuit breaker box and can add outlets and lights out of the box later if needed. Also put in a ground rod for the panel and a separate ground rod to ground the panel frames. Very simple and cheap. This would be harder to do on a roof but mine was a pergola.

My utility provides monitoring of live readings and historical from my smart meter so I never added enphase monitoring. Good luck.
 
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ret60sp

Solar Enthusiast
I wanted to mount a security camera out on the PV array and make it wired with PTZ functions, so we ran a fiber optic alongside the HVDC cabling in one conduit and ran a separate conduit to bring AC power back to the array for AC power at the PV array. Fiber optic is impervious to everything electrical and magnetic so all you need is a FO to Ethernet converter on each end to outfit your array with whatever networking gadget comes to mind.
 

SteinVT

New Member
Thanks for the posts, some things are starting to make sense. Probably should have spent more time on this forum before dropping the cash.
Ready-Fire-Aim, it wouldn't be the first time.;)

Next question, what do you suggest to use to move the AC power from the array to the garage? It's probably close to 175'. Using the tables in the Enphase manual, it looks like 4 gauge copper will have too much voltage drop. Is big Aluminum an option? Or multiple homeruns? Or just go larger copper?

And finally, where do you source the wire? Thanks-Mark
 

MarkSolar

Solar Enthusiast
Thanks for the posts, some things are starting to make sense. Probably should have spent more time on this forum before dropping the cash.
Ready-Fire-Aim, it wouldn't be the first time.;)

Next question, what do you suggest to use to move the AC power from the array to the garage? It's probably close to 175'. Using the tables in the Enphase manual, it looks like 4 gauge copper will have too much voltage drop. Is big Aluminum an option? Or multiple homeruns? Or just go larger copper?

And finally, where do you source the wire? Thanks-Mark
I wouldn't run multiple homeruns unless each is individually protected for overcurrent. I'm guessing that combiner is expensive, I don't see why you couldn't use a small subpanel as a combiner. You could get two subpanels and run separately protected lines back to the garage. 2 gauge copper really isn't that much worse to work with than 4 gauge, both are a pain if you have any tight spots and both weigh a lot to pull that far. I'd avoid aluminum unless you have someone really experienced with it do the install. The terminations have to be done correctly. I never thought about this as a side effect of microinverters, it gets really expensive to ship that much AC over a long distance.
 

SteinVT

New Member
Spent some time with the Enphase document "Calculating AC Line Voltage Rise for IQ-Series Micros with Q Cable". Finally feel comfortable with electrical design. Besides current carrying capacity, one must also limit voltage rise to less than 2% to the last inverter in the string.

The three parts of the voltage rise are the Q-cable, any extensions to a Q-cable and the home run. Using the layout from the first post my V rise from the cable is 0.18%. I will need an extension cable from the 10 panel subarray of about 20' which translates into 0.40%. The final home run is the driver in my system as I will need about 200' of cable. To keep total rise below 2% will require 2 gauge wire. The wire is capable of carrying 135a and my max generation will be less than 50a so it will be over designed regarding capacity.

As suggested by NewBostonConst and MarkSolar, I will use a small sub panel as a combiner. Looking at a Siemens 8 space, 16 circuit outdoor box. If I understand correctly, I will add (3) double 20a pole breakers which I will attach to each of the sub arrays. My home run then attaches to the panel lugs. There is no neutral bar in this panel, but I don't need one unless I wanted to add a 120v plug. But then I would need to run a neutral line ($400). My home run will be red, black (loads) and green (ground). I will return the Enphase Combiner and purchase the Enphase Envoy which will be mounted in the garage to monitor the panels.

What do you guys think? Seem about right? Thanks all for comments. - Mark

Here is what the array looks like after about 2 1/2 days of effort by myself and my wife.
Solar Array.jpg
 

MarkSolar

Solar Enthusiast
As suggested by NewBostonConst and MarkSolar, I will use a small sub panel as a combiner. Looking at a Siemens 8 space, 16 circuit outdoor box. If I understand correctly, I will add (3) double 20a pole breakers which I will attach to each of the sub arrays. My home run then attaches to the panel lugs. There is no neutral bar in this panel, but I don't need one unless I wanted to add a 120v plug. But then I would need to run a neutral line ($400). My home run will be red, black (loads) and green (ground). I will return the Enphase Combiner and purchase the Enphase Envoy which will be mounted in the garage to monitor the panels.
The 20A breakers need to be sized for 125% of expected current flow. Not sure what current you have in each subarray.

You're correct you don't need a neutral line, but make sure you're not connecting the ground wire to what is designed as the neutral bar. That is a code violation, and would cause your ground wire to become a current carrier if the two legs are out of balance.

It's hard to tell from photo but it looks like the top and bottom edge of your panels are touching. The datasheet on my panels called out a minimum spacing between edges, which was different for long and short edges.
 

SteinVT

New Member
My sub arrays put out at most 16 amps. Just lucky I guess.

The panels are separated by about 1/4”. Thanks for pointing that out, I didn’t know there was a spec. For my panels it is 10.5mm or 0.41”. I’ll make it 1/2”. I appreciate you guys keeping me straight.

Regarding grounding, I have a grounding clamp which I planned to attach to a rail and then into the combiner box and the earth wire. Anything more than that? -Mark
 

MarkSolar

Solar Enthusiast
Regarding grounding, I have a grounding clamp which I planned to attach to a rail and then into the combiner box and the earth wire. Anything more than that? -Mark
As long as there's a ground bar in the combiner box and it's not a neutral bar, that's it. Many subpanels don't come with a ground bar, you buy it separately and install it. When you say "earth wire" what do you mean? All ground conductors should lead back to the service panel where they are connected to the neutral bus. The service panel will have a ground conductor leading to a set of ground rods.
 

SteinVT

New Member
What I meant by earth wire was ground wire. Does the ground wire have to be the same size as the load wires? I have an inexpensive source for bare 6 gauge copper. Since there will be no current seems it should be fine unless there is a code requirement. - Mark
 

MarkSolar

Solar Enthusiast
What I meant by earth wire was ground wire. Does the ground wire have to be the same size as the load wires? I have an inexpensive source for bare 6 gauge copper. Since there will be no current seems it should be fine unless there is a code requirement. - Mark

Code will tell you what size ground wires need to be, the logic is the ground needs to be big enough to carry enough current for a short time to trip a breaker so the fault is isolated. You're carrying 48A at 240v, normally 10ga ground is adequate for 50A and you'd use 8ga wire. But since you have to upsize the load carriers for voltage drop,code says you have to upgrade ground proportionately. Not sure if that means by cross sectional area or what, but I think 6ga is more than adequate. If you want a definitive answer, I'd go on an electricians forum and ask the question.
 

SteinVT

New Member
According to the link provided by newbostonconst 8 gauge Cu is suggested for #2 and higher. Works for me. MarkSolar thanks for the explanation. Helps me understand.

Thanks guys. You just saved me a couple hundred dollars. - Mark
 

12kw_2021

New Member
SteinVT

I am doing a very similar ground mount install of 30 405W Trina panels with Enphase micro inverters. I plan on using a outdoor rated fuse box to combine the 310 panel strings, and the calculations say I need 3 20amp breakers one for each string. The homerun will be around 200 feet and I will be using 2 AWG copper and a 4 AWG copper ground that meet spec.

My question is have you confirmed that a single ground point on the array, with a ground wire into the combiner box meets your local code? I understand that this ground will then be continued into the home run 200 foot feed, and ultimately grounded in the home feed panel.

My local inspector is a PIA, and I want to avoid going round in circles with the guy over ground mount grounding attachments.

Thanks in advance.
 

newbostonconst

Solar Addict
I grounded the panel frames on their own ground rod....I didn't want to chance a lightening strike going through my house wiring if at all possible. This added the little cost of a ground rod.

I put a second ground rod at the breaker panel per code. @12kw_2021 mine is wired very similar to what you describe.
 

12kw_2021

New Member
Ok.. thanks for the quick reply, last question with the price of copper wire what size wires did you install for the long home run? When I run simulations I get the following:

1 AWG 200 foot run 1.65% AC Loss
2 AWG 200 foot run 1.98% AC loss
4 AWG 200 foot run 2.98% AC loss

Current guesstimate plan is to go with 2AWG at around $2.00 per foot and 4AWG for the single ground wire.

Will the code inspector care if I use less expensive wire, as long as it meets the current carry spec for the distance.

For the ground wire to your ground mount located ground rod, how many attachment points did you use on the array, one, or many?
 
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