Solar System and Backup Generator at Detached Garage

[TracerRound]

I am in the planning stages for a detached garage/woodshop and going through all of the future proofing steps regarding the electrical. My questions and scenario are for my knowledge and an electrician will be used but I like to know what I am getting myself into before hand.

The detached garage will be about 60ft from the closest point of the existing house built in 2018. The power meter is on the opposite side of the house on a walkout basement that wheels off about 230ft from where the garage's subpanel will be (includes 10ft on each side for vertical travel). This would be all trench with no obstructions besides the house and in conduit. I could shorten the distance by traversing the basement but I am not fond of putting another hole in the basement wall. I would like put a 100amp or less subpanel in the garage/woodshop as well as have the ability to tie in future solar panels mounted on the garage roof as well as a future backup generator. I would like to locate the generator there purely due to less noise for my ears as well as the neighbors (walk out is uphill and on front corner of house, detached garage would have it on the rear facing the rear five-ish acres).

My initial questions are:
1. It is feasible/realistic to have the generator and solar panel that far away given it will be fed using the proper gauge for the power and distance?

2. I am assuming I would need to run two different feeds the 230ft, one for the subpanel feeding the garage and one feeding the solar or generator to a future transfer switch/critical circuit panel located at my power main and house panels. Is two runs correct or can it be done with one feed between buildings?

In case it matters I am in NC about 60 miles north of Charlotte and in Duke Energy territory. I also have two 200amp Siemens P3040 panels directly inside from the power meter that are balanced to feed the house. I am not sure if they are both considered main panels or if one is a sub but there is no disconnect in either one for the other. Thanks for any input!

 

[wyliesdiesels]

I am in the planning stages for a detached garage/woodshop and going through all of the future proofing steps regarding the electrical. My questions and scenario are for my knowledge and an electrician will be used but I like to know what I am getting myself into before hand.

The detached garage will be about 60ft from the closest point of the existing house built in 2018. The power meter is on the opposite side of the house on a walkout basement that wheels off about 230ft from where the garage's subpanel will be (includes 10ft on each side for vertical travel). This would be all trench with no obstructions besides the house and in conduit. I could shorten the distance by traversing the basement but I am not fond of putting another hole in the basement wall. I would like put a 100amp or less subpanel in the garage/woodshop as well as have the ability to tie in future solar panels mounted on the garage roof as well as a future backup generator. I would like to locate the generator there purely due to less noise for my ears as well as the neighbors (walk out is uphill and on front corner of house, detached garage would have it on the rear facing the rear five-ish acres).

My initial questions are:
1. It is feasible/realistic to have the generator and solar panel that far away given it will be fed using the proper gauge for the power and distance?

2. I am assuming I would need to run two different feeds the 230ft, one for the subpanel feeding the garage and one feeding the solar or generator to a future transfer switch/critical circuit panel located at my power main and house panels. Is two runs correct or can it be done with one feed between buildings?

In case it matters I am in NC about 60 miles north of Charlotte and in Duke Energy territory. I also have two 200amp Siemens P3040 panels directly inside from the power meter that are balanced to feed the house. I am not sure if they are both considered main panels or if one is a sub but there is no disconnect in either one for the other. Thanks for any input!

What you propose is a complicated setup


You cannot do this with one feed to the shop. no way to isolate the generator power from the grid at the house and still power the house with just one feed. The transfer switch needs to be where the grid power comes in at.

If you have 2 panels in the house with no disconnect ahead of them between the meter, then they are both main panels. you would need to put the transfer switch in between the meter and both panels. This means the panels would then need to be changed to subpanels- 4th wire added and the neutral bars isolated. this also potentially means adding ground bars and moving grounds over to the new bars.

Ok, so do you want an automatic transfer switch? If so, the gen would need to be sized to handle the entire load or you would need load shedding modules.

Also, the solar would need to disconnect from the service if the generator kicks on. If youre running an ATS, then you would need an automated disconnect on the circuit connecting the solar inverter to the service as I'm not aware of a solar inverter that will sync and play nice with a generator.

 

[tyme2par4]

If you put the generator at the garage, it would need it's own dedicated feed, or you would only be able to power the garage with it.
Solar panels can be connected through a sub panel, but there are some extra hoops and calculations that have to be done. It's not super common, so I would have to look up exactly how to do it.
Or you could run the DC wiring all the way to the house and mount the inverter near the main panel. This would require smaller wire, because you'll likely be operating at 500 volts as opposed to 240.

 

[TractorJeff]

I think he said there is no disconnect in either of the 2 Panels.
This leads me to believe He states the Main Disconnect is closer to the Meter?

 

[TracerRound]

Thanks for the replies. I figureded two feeds would be required. I am pretty sure I would be putting in an ATS but not sure if I would add a subpanel for critical circuits to be rewired to or size the generator to cover the whole house. No LP/NG and we have two A/C units with heat pumps.

From researching solar inverters there are ones that have a backup generator connection but I am not sure that would work in this scenario. I know both the solar and generator power will need to be interconnected via a transfer switch between the meter and house panels so the solar and generator are isolated from each other.

I am not sure if this would require transfer switches at both behind the meter as well as at the garage or if its possible to put the solar inverter at the house. I think that would lead to needing three runs between the buildings (subpanel, solar, generator).

I am wondering if after figuring a theoretical working layout that the requires wire size and distance would make it financially impractical. The solar panels would have to be on the garage due to facing south but the generator could be located at either building, just preferred at the garage.

Thanks again for going down the rabbit hole on this scenario.

 

[wyliesdiesels]

Can you post pics of your meter and panels

 

[TracerRound]

I have lurked for about a year but have not reached my five post minimum for photos.

 

[TracerRound]

Regarding the panel, are you just wanting to know available space or a photo with the cover removed?

 

[Noltz]

I like the idea of what you're saying, but it's financially impractical. I'm picturing something like this?



I've actually been pondering this question for like 45 minutes now LOL.

The generator idea is pretty much a no-go, especially roof mounted. You'd need certified plans that would support a running engine on the roof. A generator that can run a house with a 400A input. That's a big genset. Standby gensets run once a week for 20-30 minutes. You said you don't have LP or NG at the property, so you need to consider fueling it. How much fuel will you store and where? How will you get it up to the generator? Are you willing to shut it down to refuel it in an extended power-out situation?

Solar panels can be located on the shop roof and your house too if you want. I'd install the battery bank & inverters in the house with a grid tie system. Depending on how many panels you install it might save you money long-term. But can it run your AC and heat pumps? I suspect it would quickly deplete the battery bank. They're just not power efficient. Can you be reasonably comfortable without them? Or do you have some other source of heat like a wood fireplace. Would you be willing to forgo air conditioning in those cases? Or maybe put just those circuits onto a conventional Generator backup with an ATS and a nice big propane tank?

I like rabbit hole scenarios so I'm gonna dive into it a bit. I'm not an electrician and would defer to Wylie if he said I used the wrong cap on my toothpaste here, so this is just a brain teaser to me. Technically it's possible to re-route the shop feed line to feed main panels, but not legally& it's entirely impractical.

You have two main panels now. We will call them Panel A and Panel B. We'll say Panel B feeds the garage through a 100A breaker.

First an ATS that breaks the connection of Panel A from the Utility power. Second is an ATS that flips Panel B from Utility power to a 100A breaker in the bottom of Panel A. Maybe need a load-shed module to drop the high-draw heat pump. I'm unfamiliar with grounding requirements, but you'd need at least contactors that would isolate the Neutral bond in the panel and another to connect a ground conductor between Panel A and B. Not doing this might prevent your breakers from functioning. Finally you'd need yet another ATS that would disconnect the Garage Panel feed and connect it to the Generator output. Not sure what requirements would be needed on the ground side there.

I spent way too much time thinking about this and deleted 2 prior posts.

 

[beelsr]

I have lurked for about a year but have not reached my five post minimum for photos.

almost there....

 

[wyliesdiesels]

I like the idea of what you're saying, but it's financially impractical. I'm picturing something like this?



I've actually been pondering this question for like 45 minutes now LOL.

The generator idea is pretty much a no-go, especially roof mounted. You'd need certified plans that would support a running engine on the roof. A generator that can run a house with a 400A input. That's a big genset. Standby gensets run once a week for 20-30 minutes. You said you don't have LP or NG at the property, so you need to consider fueling it. How much fuel will you store and where? How will you get it up to the generator? Are you willing to shut it down to refuel it in an extended power-out situation?

Solar panels can be located on the shop roof and your house too if you want. I'd install the battery bank & inverters in the house with a grid tie system. Depending on how many panels you install it might save you money long-term. But can it run your AC and heat pumps? I suspect it would quickly deplete the battery bank. They're just not power efficient. Can you be reasonably comfortable without them? Or do you have some other source of heat like a wood fireplace. Would you be willing to forgo air conditioning in those cases? Or maybe put just those circuits onto a conventional Generator backup with an ATS and a nice big propane tank?

I like rabbit hole scenarios so I'm gonna dive into it a bit. I'm not an electrician and would defer to Wylie if he said I used the wrong cap on my toothpaste here, so this is just a brain teaser to me. Technically it's possible to re-route the shop feed line to feed main panels, but not legally& it's entirely impractical.

You have two main panels now. We will call them Panel A and Panel B. We'll say Panel B feeds the garage through a 100A breaker.

First an ATS that breaks the connection of Panel A from the Utility power. Second is an ATS that flips Panel B from Utility power to a 100A breaker in the bottom of Panel A. Maybe need a load-shed module to drop the high-draw heat pump. I'm unfamiliar with grounding requirements, but you'd need at least contactors that would isolate the Neutral bond in the panel and another to connect a ground conductor between Panel A and B. Not doing this might prevent your breakers from functioning. Finally you'd need yet another ATS that would disconnect the Garage Panel feed and connect it to the Generator output. Not sure what requirements would be needed on the ground side there.

I spent way too much time thinking about this and deleted 2 prior posts.

yeah what he wants "could be" accomplished with some modifications and a whole lot of engineering and money.

as you said, its not practical financially and i doubt the OP has money for such a thing.

 

[wyliesdiesels]

I have lurked for about a year but have not reached my five post minimum for photos.

post a few more comments then... whatchya waitin for?

Regarding the panel, are you just wanting to know available space or a photo with the cover removed?

pics of meter pan and any panel(s) next to it, pics of panels with deadfronts on and off....

without seeing what you have, its a WAG as to what needs to be done...

 

[TracerRound]

Not sure where the roof mounted generator part came from but it would be on the ground.

 

[TracerRound]

Thanks again for the replies. I was able to take photos and should have them attached now. I guess my real question is how many conduits for power and what size to put in the ground to be able to accomplish this if its even possible. I may never add either a generator or a solar panel system to my not event built garage/workshop.

Sent from my SM-N960U using The Garage Journal mobile app

 

[wyliesdiesels]

Not sure why youre thinking the panels dont have main disconnects. They both have 200a mains just above the branch breakers.

 

[TracerRound]

Sorry for the confusion. I meant that one panel didn't have a disconnect for the other making one a subpanel. I had not seen two main panels before we built this house.

Sent from my SM-N960U using The Garage Journal mobile app

 

[Noltz]

Not sure where the roof mounted generator part came from but it would be on the ground.

the ability to tie in future solar panels mounted on the garage roof as well as a future backup generator.

*emphasis is mine.

My mistake. I have seen rooftop generators before but never on residential and certainly never when the owner has 5 acres behind them. My mistake.

 

[pr3dict]

I'm kinda doing something like this right now...

I have solar already on the house that net meters to the grid which is great. This is actually connected BEFORE my main breaker.

So the way it works is:

Utility power -><- Solar -> Main breaker -> ATS (Automatic transfer switch)

From the ATS that's at the house it has an input from the generator that is at my detached garage. That's 300ft of 4/0 AL for a 22kw. I have a 500 gallon LPG tank being installed next week at the garage also for this.

ATS then connects to what essentially is now a sub panel aka my main breaker panel for the house.
Thennnnnn I have 100 amp breaker in that panel that runs 300ft of 1/0 AL to the sub panel in the garage.

I fit all this in a 2 1/2" sch 40 conduit. Also shared the ground between the Generator and sub panel because technically you are allowed to if there are irreversible connectors between the feeds. All in all it was 3 4/0, 3 1/0, 1 #2 (for the ground), 6 #12 (control wiring for the generator). I HIGHLY recommend not doing that though. Put 2 or 3 different conduits in the ground it will make your life 10000 times easier.

So what you are asking is essentially possible but you are going to pay a lot of money in cable and conduit to make it happen. It was a PITA. I had to get a big cable puller to pull all the wire and I think I spent like $2500 in cable and conduit. But. The generator is at the garage lol.

 

[wyliesdiesels]

How does your solar inverter tie in before a main breaker?

 

[pr3dict]

How does your solar inverter tie in before a main breaker?

Solar was installed before I bought the house but it seems the lines coming from the inverter are tapped on the "Utility/Source" side of the main breaker.

 

[gpiggaz]

Solar was installed before I bought the house but it seems the lines coming from the inverter are tapped on the "Utility/Source" side of the main breaker.

I think that is called a "line side tap" it is usually used when your main bus bar isn't big enough to meet the 120% rule- At least that is my understanding of how that works. In Tucson, they have a way to actually do that in the Meter Socket.

I'm in the process of installing a ground mount system at my house and I made sure I could backfeed in my main panel, the Line Side tap complicates things in my opinion, and unless you generate a lot of power or have a small main bus, it's much easier (in my opinion) to just do a backfeed breaker

 

[wyliesdiesels]

Solar was installed before I bought the house but it seems the lines coming from the inverter are tapped on the "Utility/Source" side of the main breaker.

is there overcurrent protection between the inverter and the tap?

 

[pr3dict]

is there overcurrent protection between the inverter and the tap?

If it's according to code there better be lol.

 

[wyliesdiesels]

If it's according to code there better be lol.

yup thats why i asked

 

[tyme2par4]

I think that is called a "line side tap" it is usually used when your main bus bar isn't big enough to meet the 120% rule- At least that is my understanding of how that works. In Tucson, they have a way to actually do that in the Meter Socket.

I'm in the process of installing a ground mount system at my house and I made sure I could backfeed in my main panel, the Line Side tap complicates things in my opinion, and unless you generate a lot of power or have a small main bus, it's much easier (in my opinion) to just do a backfeed breaker

Yup, theres actually a company that makes a device that piggybacks on the back of the meter where you can make your connection. It's approved by a handful of PoCos.

 

[Bretny]

What's the cost to make the main pannel your garage pannel and run the house as a sub pannel?

 

[dcg9381]

I have this setup. Sorta.
My utility feed is 320A service, which is split and fed into 2 x 200A main panels.
One of those panels feeds the shop on a 100A breaker. The shop has 20 x 300W solar panels and a single inverter.

The second panel feeds the residence - 200A. The house will likely have solar in the future and currently has a 20KW generator / ATS. You cannot be in a situation where the solar might suppliment (or backfeed) the generator.

In order to accomplish this, the house solar inverter has to be upstream of the generator ATS. That way, if the grid fails, the solar inverter shuts down, and downstream of that the ATS switches over and turns on the generator....

I can do a diagram if necessary.

Downside of this, my shop is not on generator backup power.


If there is a way to do solar in combination with active backup generator power - I don't know what it is. My guess is that you CAN get these solutions from inverter manufacturers, but they need to do power regulation...