Where to connect grid tied solar - Generator, 2 ATS, and 2 Inverters

[Mr. Inquisitive]

I have been diving into solar as of late. I did my first owner build solar system 1.5 years ago with an 11.4 kW system (qCell/SolarEdge) and it is working great. I did my own design, component selection, etc.

Now I am working on a system for my daughter, but her situation is much more complicated. While her electrical is grid tied, she is in a forest area and has frequent power outages. This necessitates a 11kW Generac generator (model 0064391) which is connected to two ATS' (model RTSW200A3). The power is distributed to the house and a 1k sq' garage (two buildings approx. 350' apart). The generator, ATS' and grid connection are in between the two buildings. The solar panels will be located on the garage roof. There is a 200A sub panel on the garage, a 200A sub panel on the house, and a free standing main panel in between the two buildings.

To this existing setup, I will be connecting 2 SolarEdge Inverters (SE7600H-USSNBBL14) each having 13 Qcell G10+ panels connected. (I will eventually expand to more panels).
Freestanding panels (front).jpgFreestanding Panels(back).jpgATS#1.jpgATS#2.jpgATS Wiring Diagram.jpg

So now for the question ....
I have read everything I can find on this forum and in the Generac install guides/owners manuals. I know in another thread it was mentioned that the solar should be connected to the grid side of the ATS. Would that be where I am seeing the 0/1 gage wires in ATS1 (N1/N2)? If so I am assuming I can't connect the inverters to the subpanel at the garage but will need to trench a second run from the garage to the ATS? Or can I tie into the subpanel (fed by T1/T2)?

As with other posts I have read, my primary concern is back-feeding the generator and blowing it up. I did read some discussion about the output frequency of the generator being tweaked as to not fool the inverters into thinking the grid is up, however I am not seeing how to do this in the manuals. In my attempt to contact Generac to get more info, I sat on hold for 2 hours before I finally hung up. I am hoping one of you incredibly bright minds will share your thoughts.

[oregon_phil]

I have a Kohler generator and solar.

If you have access to your meter base panel, please get the part number and take pictures of what's inside. I am assuming this is a meter base with breakers in it but meter base part number and pictures would help. Please be careful.

Your schematic doesn't show how everything is connected.

[Mr. Inquisitive]

The main panel is a Square D SU3040D400CB 400A panel. I will have to post the wiring behind the cover later but here is the breaker layout.
Main Panel 1.jpg

The schematic I previously provided is just the generic schematic from Generac for the ATS. The wires entering the first ATS on the top are from the main panel. Unfortunately, the equipment was all installed before my daughter bought the home and no documentation is on file with the county (according to the county, which is hard to believe) and we don't know who installed it. All I have is what is shown. I will likely have to tone out lines to verify connections since the sub panels are 100+ feet from the main.

[DanS26]

Does the garage have to have backup power? If not, eliminate the second ATS and repurpose the garage wiring to connect to the utility supply side. Then attach the inverters to the garage subpanel. No digging and no extra wire.

[Mr. Inquisitive]

Hi Dan. Yes the garage does need backup power as it is used as a living space occasionally (full bathroom, etc.).

[DanS26]

Well then I would suggest to run high voltage DC to string inverter mounted next to the main panel. Less wire cost for the 300' run.

Good luck!

[oregon_phil]

The main panel is a Square D SU3040D400CB 400A panel. I will have to post the wiring behind the cover later but here is the breaker layout.
Main Panel 1.jpg

The schematic I previously provided is just the generic schematic from Generac for the ATS. The wires entering the first ATS on the top are from the main panel. Unfortunately, the equipment was all installed before my daughter bought the home and no documentation is on file with the county (according to the county, which is hard to believe) and we don't know who installed it. All I have is what is shown. I will likely have to tone out lines to verify connections since the sub panels are 100+ feet from the main.

I am not an electrician nor a EE so take anything I say with a grain of salt. I am a retired ME with design and process experience.

I think this is your setup. You can confirm it when you are on site.

My generator only has one transfer switch and it is wired up exactly like xfer switch 2. My solar is connected to the same breaker panel box as the 125 amp garage breaker. When the power goes out, solar goes off line, then my transfer switch transfer power from the generator to my house panel.

Hooking up one inverter would be pretty easy, but you can't put two inverters on the meter breaker panel because of NEC 120% rules. The other inverter probably needs to go after the house disconnect switch but before the utility connection on transfer switch 1.

But remember I'm an ME and you should talk to an electrician for sure. I just like to untangle seemingly messy issues if I can help.

Good luck!

[Mr. Inquisitive]

Hooking up one inverter would be pretty easy, but you can't put two inverters on the meter breaker panel because of NEC 120% rules.

I am not sure if this is the case. The main panel is a 400A panel. The inverters are 7.6kW inverters. would that really exceed 120%? Or am I misunderstanding what you are saying?

[Mr. Inquisitive]

Well then I would suggest to run high voltage DC to string inverter mounted next to the main panel. Less wire cost for the 300' run.

I will have to give this some thought. It is 2 inverters so I think I would need to run 2 sets of DC vs 1 set of AC if I put the inverters at the garage. I don't intend to go over 14kW total in the long term so this should be doable on a single AC run.

[DanS26]

I will have to give this some thought. It is 2 inverters so I think I would need to run 2 sets of DC vs 1 set of AC if I put the inverters at the garage. I don't intend to go over 14kW total in the long term so this should be doable on a single AC run.

Yes....4 wires of large diameter of aluminum or 4 wires of slightly smaller copper for AC vs 5 wires of smaller diameter copper for DC. Voltage loss caclculation will be very important.

[oregon_phil]

I am not sure if this is the case. The main panel is a 400A panel. The inverters are 7.6kW inverters. would that really exceed 120%? Or am I misunderstanding what you are saying?

To clarify, the meter base is connected to the house 200 amp service disconnect and garage 200 amp service disconnect. The garage 200amp service disconnect is connected to 30 space/40 circuit breaker panel with 200 amp buss bars (assumed, doesn't specifically say). You can connect one inverter to buss bars. But there might be other ways to do what you want. Best talk to an electrician.

[oregon_phil]

I will have to give this some thought. It is 2 inverters so I think I would need to run 2 sets of DC vs 1 set of AC if I put the inverters at the garage. I don't intend to go over 14kW total in the long term so this should be doable on a single AC run.

I read this to say you would run an additional set of AC lines for the inverters.

Questions to help you figure out the details:

1) How do you combine two inverters at the garage?
2) Two 7.7 inverters is 80 amps worth of breakers at the meter breaker panel. You have a 200 amp service disconnect at the meter base for the garage unit. What does the service disconnect need to be decreased to in order to fulfill the 120% rule? Does this set up still work?

[DanS26]

The new and additional garage main breaker will have to be derated to 150 amps. Two 40 amp breakers installed at the bottom of the garage panel accepting load from each inverter. Make sure AHJ is OK with this since some jurisdictions require a blade disconnect instead of breakers. Remember this new garage panel cannot interact with the existing garage panel.

IMO I would not go this route.....instead run 5 wires of high voltage DC to inverters at the 400 amp load center 300ft away.

[Mike 134]

I see Oregon Phil listed his profession so the OP could have an idea about his skill set. How about the rest of you just handymen putzing with electrician stuff?
Myself 38 years feeding my family as a journeyman electrician, you might have noticed I didn't offer advice, to many unknows in a forum post.

[DanS26]

I see Oregon Phil listed his profession so the OP could have an idea about his skill set. How about the rest of you just handymen putzing with electrician stuff?
Myself 38 years feeding my family as a journeyman electrician, you might have noticed I didn't offer advice, to many unknows in a forum post.

Mike, there are parts of the country that the NEC is just a suggestion. No inspections, no nothing.....if your house burns down that is your problem.