PV Grounding Question for Multiple Arrays

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IslanderVT

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I'm working on a grid-tied ground mount solar project that has three separate arrays of 12 modules each, which are somewhat spread out on the property. The system uses microinverters (APSystems DS3-L) so two solar modules plug into each microinverter, and from there its AC all the way back to the utility.

All three ground mount arrays have 4-space loadcenters that act as combiners with 2 breakers protecting three microinverters each using 12AWG trunk cables. From each array loadcenter, 6AWG runs in buried conduit back to a central load center that combines all three arrays into a single home run feed, and also houses the PV disconnect breaker and solar generation meter.

Each array has its own 10AWG EGC, and all three tie together in the central PV load center. This central PV load enter is fed from the residence using a 4-wire MHF in conduit with a 4AWG ground that ties back to the single neutral-ground bond in the home's main load center.

My question is about ground rods. We plan to install the standard two 8' ground rods at the central PV load center, which is mounted to the first array. This first array is about 100' from the residence. This takes care of re-establishing the GEC away from the residence.

For the other two arrays, which are about 70' and 100' from the first, should I place ground rods at each of these arrays also? Or maybe one on each? Or should I just consider the EGC's from the central PV loadcenter to be a sufficient ground? Doing this would make it a single-point ground back at the central PV loadcenter.

My initial thought is that at least one ground rod at each array would provide the best protection.

But I'm also concerned about creating ground loops by tying together multiple ground rods and array frames...so that's why I'm asking.

I'd appreciate your thoughts on this....Thanks!
 
The NEC since 2017 simply requires a grounding electrode system at each array. If your ground mounts are using steel supports in the ground then the arrays are effectively grounded anyway, but the NEC wants at least one such such support to be 10ft into the ground. Otherwise, drive two ground rods at each array.

I don't see any ground loops in your description, nor do I see why you should worry much about that.

As far as what 'protection' the ground rods provide, basically nothing if the ground mounts already have a bunch of steel in the ground. If you happen to be using some non-earth-penetrating support method, then the ground rods may provide a modicum of protection against shock in the case the racking somehow becomes energized without tripping a breaker. If you're concerned about protecting the equipment from lightning, consult an LPS expert because the NEC does not have you covered there.
 
Thank you jaggedben for the insight!

We're using the Nuance Osprey platform, so it does not have ground penetrating ground screws...but it does have 6 galvanized plates about 12" square that sit on the soil. To stay compliant, we will drive double ground rods at each array.

We'll plan to tie these in at each array with the EGC's that come from the central PV loadcenter. This will complete what seems to be very solid grounding plan for the whole system.

What would you recommend for a surge protector strategy?

The loadcenters are all SquareD, so we are currently planning to put in a Whole Home SPD in the central loadcenter. https://www.se.com/us/en/product-ra...ter=business-5-residential-and-small-business

Should we also place SPD's at each array? Location is moderately prone to lightning, but not severe. What would be best practice? These would be easy to add: https://www.se.com/us/en/product/HE...rotective-device&selected-node-id=12368269215

Thanks again....I really appreciate the support!
 
If your POCO is supplying 3 wire service to your main disconnect then why would your mini-POCO micro-inverter service use four wire service to your main disconnect?

Seems to me you are inviting a lightning strike at the array into your main disconnect at the house/business. They are both separately derived power sources. That 4th 4AWG ground wire will carry a significant high voltage event right into the house/business. Not only not needed but probably dangerous.
 
DanS26 said:
If your POCO is supplying 3 wire service to your main disconnect then why would your mini-POCO micro-inverter service use four wire service to your main disconnect?
Click to expand...

Perhaps because code requires it.

Seems to me you are inviting a lightning strike at the array into your main disconnect at the house/business. They are both separately derived power sources. That 4th 4AWG ground wire will carry a significant high voltage event right into the house/business. Not only not needed but probably dangerous.
Click to expand...

I don't see how the 4th wire makes any serious difference. Also it looks to me like those inverters don't require a neutral so it could still be 3-wire. Regardless, you'll have a grounded wire between structures either way, and lightning doesn't care if the wire is white or green. Also there's nothing separately derived here, nor do I think that having power sources at the arrays instead of some other kind if structures with loads makes any real difference (other than the PV equipment might be more valuable to protect from damage).

I'm not saying that your comment is completely offbase. I'm sure there is indeed a danger of a lightning discharge traveling along the connections between arrays. I imagine that the right combination and arrangement of surge protectors and perhaps ground rings or something would provide some worthwhile protection. But I declined to answer the question about that above because I lack the credentials or experience to offer strong opinions on the details. All I can say is I think that surge protectors like the one he posted can't hurt, and I'd put one to both neutral and ground at each array if the neutral is actually present there.
 
I wonder what Mr. Holt would say about this matter? Since this is his forum and he has expressed much advice on ground systems and the dangers lurking, I would much appreciate his comments.
 
Thanks everyone for the helpful replies.

In addition to feeding the solar arrays, the feed from the residence also feeds two outbuildings (sorry for not mentioning this before...I was trying to keep it simple). The system does have a neutral, which is not used for the microinverters, but is needed for the outbuildings. The feed from the residence first goes to a load center with feed-thru lugs for general loads needing a neutral, then feeds the solar generation meter and the central PV loadcenter without a neutral.

We are certainly concerned about the solar equipment inviting a lightning strike that impacts the residence, but as jaggedben points out, code requires a 4-wire feeder for outbuildings. My understanding is that solar arrays are included in this. This is why I've been asking about grounding and surge protection strategies to mitigate that risk.

We appreciate the feedback on surge protection. We'll likely go ahead and install one on each array...it seems like a prudent addition considering the cost of the equipment involved.

It seems like a lot of solar installers like to use the Midnight Solar lightning arrestor:

MidNite Solar Inc. Renewable Energy System Electrical Components and E-Panels

MidNite Solar is the industry leader and manufacture of quality Renewable Energy System electrical components and E-Panels.
www.midnitesolar.com www.midnitesolar.com

Does anyone know if the Midnight unit has advantages over the standard Square D units for a solar array application? Cost and hookup are about the same...wondering if there is a performance difference?
 
Where in the code does a solar array structure with it own contained inverter power source to be deemed an outbuilding?

I'm not challenging your reference to code, I just can't find it.
 
Yes...we're considering each solar array to be a separate structure on the basis that each one has its own set of dedicated buried conductors.

Each has its own disconnect in the form of two breakers per array, which protect the 12AWG microinverter cables before they are combined into a 6AWG buried feeder.

We're happy to add ground rods to each one as this is the best protection for the system. These will be tied to the ECG's for each array which are run with the buried conductors, and originate in the central PV loadcenter. This loadcenter is tied directly to the residence GEC with the 4AWG ground in the MHF home run. The only Neutral-Ground bond exists in the main panel of the residence.

Currently we're leaning toward the Midnight Solar SPD devices at each array....they have a better warranty, and are Made in USA by a company of solar geeks.
 
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