Need help with solar panel array design for apartment building

[mikael6]

I am in process of designing a solar panel array for a flat roof apartment building in New Britain, CT. This is my first solar panel array install. I based my design partially on another design that a friend of mine had installed. I already have my inverter, wiring, dc disconnect, ac disconnect, conduit, combiner box. I haven't purchased the panels or mounting system yet as I don't want to purchase until I have gotten some feedback on my design. I used the sunnyboy design tool to help me figure out # of panels, strings, etc. I want my design to be able to accomodate future expansion without having to change out combiner box, disconnects, etc. I might be ok with swapping out my inverter in future if I need a larger one.


Anyway, could you all take a look at the attached design and let me know of any feedback you have.

Specific questions are:

1. is the 15 amp fuse in combiner box sufficient
2. is my 8 gauge wiring sufficient
3. are my ac and dc disconnects appropriate for the system
4. what size fuse should I use in my ac disconnect
5. what size breaker should I use in my electric service panel
6. Is there anything missing from my system
7. are there any mistakes in my design

[green]

One question first. Are you renting this appartment or do you own the complex. I worked for a property management company for years and this would have never been approved for a tennant. I was the head of maintenance and without an agreement me or one of my guys would have gone up, snipped the wire and took your panels, evict you, and then sued you for the damage to the roof.

Just wondering,
Green

[mikael6]

I own the complex.

[green]

I own the complex.

Ok so you know exactly what I'm talking about.

I just wanted to be sure, you'd be suprized at the crazy stuff people come on here wanting to do.

Green

[Naptown]

I am in process of designing a solar panel array for a flat roof apartment building in New Britain, CT. This is my first solar panel array install. I based my design partially on another design that a friend of mine had installed. I already have my inverter, wiring, dc disconnect, ac disconnect, conduit, combiner box. I haven't purchased the panels or mounting system yet as I don't want to purchase until I have gotten some feedback on my design. I used the sunnyboy design tool to help me figure out # of panels, strings, etc. I want my design to be able to accomodate future expansion without having to change out combiner box, disconnects, etc. I might be ok with swapping out my inverter in future if I need a larger one.


Anyway, could you all take a look at the attached design and let me know of any feedback you have.

Specific questions are:

1. is the 15 amp fuse in combiner box sufficient
I would use a 10A fuse but none is required at this time as there is only one string. Once you get to more than 2 strings only then are fuses on each string reuired
2. is my 8 gauge wiring sufficient
More than enough for now and you could add 2 more strings on to it
3. are my ac and dc disconnects appropriate for the system
The DC disconnect comes with the inverter (It is that box mounted below) The AC is only required if the utility requires it or the local AHJ.
4. what size fuse should I use in my ac disconnect
With #8 wire 40A maximum
5. what size breaker should I use in my electric service panel
No larger than 120% of the bus bar ratings (Example a 200A panel with a 200A main you could use a 40A breaker On a 100 A box with a 100A main you could use a 20A If the panel you have has bus bars rated at 125A and a 100A main breaker than you could use a 45A breaker.
6. Is there anything missing from my system
7. are there any mistakes in my design

You seem to be going inside and out a lot on this. Is theft of the inverter a problem potentially. if not I would just mount that near the meter and you have your DC disconnect and Utility disconnect all in the same location and box. In this case no AC disconnect would be required the breaker in the panel would suffice.

[mikael6]

Thanks for response. This is really helpful. Some notes below:

3: My inverter didn't come with a dc disconnect (I got it used). I purchased a dc disconnect separately. My utility requires an AC disconnect and it must be mounted outside, not inside

I am mounting my inverter and dc disconnect inside as I am worried about vandalism as there are a lot of college kids in the area and I think there would be issues with having this stuff outside. I am locating the AC disconnet outside only because the utility company requires that.

[Naptown]

Thanks for response. This is really helpful. Some notes below:

3: My inverter didn't come with a dc disconnect (I got it used). I purchased a dc disconnect separately. My utility requires an AC disconnect and it must be mounted outside, not inside

I am mounting my inverter and dc disconnect inside as I am worried about vandalism as there are a lot of college kids in the area and I think there would be issues with having this stuff outside. I am locating the AC disconnet outside only because the utility company requires that.

then please check the model number again on the inverter. There is typically a US after the model number . If not it may not be approved for use here.

[mikael6]

then please check the model number again on the inverter. There is typically a US after the model number . If not it may not be approved for use here.

Sorry about that. It does have that in the model but I didn't write that in.

[mikael6]

Another question related to electric service panel.

The service panel itself is rated at 125 amps max. It has two hot 3 gauge copper wires that terminate at a 60 amp breaker shut off. There is also a 3 gauge copper . There are 6 slots for breakers that are all taken up currently. See attached photo. Currently there two single pole 15 amp breakers, a 30 amp double pole breaker, and two single pole breakers that have two 15 amp switches on each. So, I'm not sure how to size the breaker. Would the max breaker size with the 120% rule be 85 amp? What would you recommend in terms of sizing the breaker. Also, any recommendations on opening up a slot for the new breaker?

[Naptown]

The bus bars are OK you just dont seem to have room.
Panel replacement seems the best option that I can see.
Also is this a sub panel meaning there is another disconnect or shut off somewhere else or another panel this is fed from?

[mikael6]

Where the service comes into the building it hits a disconnect box that disconnects power for all of the electric service panels. There are 7 panels. One for each of the six apartments and an owners panel (which I will be connecting array to). From this main disconnect, 3 wires go out to the seven electric service panels. The wires are labeled 600 V MTW 4/0 AL, type THW, heat and moisture resistant, kaiser aluminum symru 75090. The owner panel isn't really a subpanel of the others. Each of the seven panels has its own electric meter.

I have done a decent amount of electrical work before but have never replaced a panel. However, it doesn't look that complicated, particularly in light of the fact that there is a main shut off for the whole building. So, I am thinking I could turn off power to the building (of course notify tenants in advance, that will be fun) install a new panel with more slots and then turn power back on. I should be able to do this without having to disconnect the power meter (which would of course involve arranging with the utility company).

What would you recommend in terms of a panel to buy (brand, how many slots, max amp rating) Would I keep the same 60 amp main shutoff for the panel? Also, with a new panel situation, what would you recommend for breaker size for the solar array?

Many thanks as I am really excited about installing my array and greatly appreciate your help. It means a lot to me

[Naptown]

I would recommend you hire a licensed electrician to do that work.

[russ]

There is a lot of legal liability involved in the event of a fire due to an incorrect installation.

[inetdog]

Another question related to electric service panel.

The service panel itself is rated at 125 amps max. It has two hot 3 gauge copper wires that terminate at a 60 amp breaker shut off. There is also a 3 gauge copper . There are 6 slots for breakers that are all taken up currently. See attached photo. Currently there two single pole 15 amp breakers, a 30 amp double pole breaker, and two single pole breakers that have two 15 amp switches on each. So, I'm not sure how to size the breaker. Would the max breaker size with the 120% rule be 85 amp? What would you recommend in terms of sizing the breaker. Also, any recommendations on opening up a slot for the new breaker?

Not that it make a lot of difference since you have no slots in the panel, but 120% of 125 is 150. (150 - 60) is 90, not 85. It should not be any larger amperage than you need for the backfeed based on the maximum inverter output. It also have to be low enough amperage to serve as protection for whatever gauge wire you run between the inverter and the breaker.
Your two 5 amp breakers with two handles on each are actually pairs of breakers which fit in to the same space as one full sized one. If there were a way to replace some of the other breakers with twin units, you would get more bus space.
If your GTI output will be 240 volts, you need a space for a double breaker though, and getting back that much space would be a problem.
A licensed electrician will be able to tell you whether a line-side tap would be allowed by your AHJ and would be less expensive than replacing your panel. Or moving some of the circuits from your owner's panel to a new sub-panel.
The clean solution is to install a new service panel as everybody else is recommending.

[mikael6]

Ok, this is great info. I agree with you all that at this point it is over my head. I will contact some electricians to get their suggestions and quotes. Thank you all for your time. Your help is truly appreciated.