5KW System Design Help Requested - Array Disconnect location

Status
Not open for further replies.
S

Scratchbuilt

Member
Location
Denver, CO
Hello all,

I would like to get some input here as to a Utility Interactive system I am installing for a client of ours. I am fairly new to the PV realm so I have some questions regarding the disconnect locations and other things that I would like to clear up. This system is BIPV (shingles) and consists of the following:

- 12 strings (paralleled) of 10 modules (series)
- Isc for each string is 5.5A
- Inverter is rated at 5KW continuos, 100A DC max. input current, 108A max input SC current
- Inverter will be located remote from the PV array (approx 100' conduit run length) and is located inside on the opposite end of the building, where the main electrical service is located.

My questions are:

1) Isc @ STC for array is 66 amps (5.5A x 12). 66A x 1.25 x 1.25(690.8 (B)(2) = 103A. My conductors will be # 2 THHN for the output circuit. I will only have one output circuit (from combiner) to the inverter. I will need to install a disconnect for the PV output circuit on the outside of the building per 690.14 (c)(1). I plan to install a 200A 2P non-fused disconnect. Does this disconnect need to be fused with a 110A DC fuse? I dont think it does since there is only one output circuit that will be connected to the inverter, right?

2) I think I know the answer to this one but I will ask it anyway. Would it be acceptable to install a 100A disconnect instead of the 200A disconnect since Imp is 97A and max input current for the inverter is 100A (max. input short circuit current is 108A)?

3) I would like to not install the 200A array disconnect on the outside of the building (aesthetic reasons). I know that as long as the output conductors are in conduit once they enter the building, and ran in conduit to the inverter, then the array disconnect can be located remote. 690.14 (C)1 Exception and 690.14 (C)5. My question is how remote can the disconnect be located once the PV Output conductors enter the building in conduit? 5', 10', 100'? I cant find anywhere in the Code that mentions distance so I am assuming that I can put the array disconnect in the Basement along with the inverter as long as the output conductors are in conduit, right?
 
S

SolarPro

Senior Member
Location
Austin, TX
Those are pretty atypical design numbers. Most PV arrays these days operate between 300 and 400 Vdc, with a max open circuit voltage of 600 Vdc. That being the case, a typical 5 kW PV system might have 2 to 4 PV source circuits.

What is the make and model of the inverter you are using? Also, what are the other module specifications (besides Isc = 5.5A)?
 
S

Scratchbuilt

Member
Location
Denver, CO
Here are the specs:

Manufacturer - Atlantis Energy Systems
Model - Tall Slate TS125GM
Power - 46W
Isc - 5.5A DC
Voc - 11.3V DC
Impp - 5.11A DC
Vmpp - 9.0V DC

Voc is calculated at 113V DC for each string (10 modules per string).

This system was designed by Atlantis Energy Systems and we are installing it for our client.
 
B

BillK-AZ

Senior Member
Location
Mesa Arizona
Please post the inverter specifications. This inverter does not show up in the California approved list (a good source of info) nor on a Google search. Are you sure it is UL Listed to UL1741? It may be a private branding of a more common inverter.
 
J

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
Yikes. Yet another reason to stay away from 'solar shingles', in my opinion.

Bill's question is also my first question.

Also, if the shingles are only 11.3VDC each, why not string together, say, 40?
 
S

Scratchbuilt

Member
Location
Denver, CO
Strange. It doesn't really come up does it? Try searching for Sunergy ELV 240. That is what came up when I searched for it and that is the one that was supplied to us. It is a Canadian company it appears. I would assume it is listed for use in U.S. I better check!

Our client just kind of bought everything from them (Atlantic Energy Systems) and it all just showed up one day and he said " OK. Lets install this. They said all this will work". We consulted some on the initial design but then didn't hear anything for about 3 months. Then all of a sudden all this shows up. It's been an interesting (read: frustrating)project to say the least.
 
J

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
Scratchbuilt said:
... My question is how remote can the disconnect be located once the PV Output conductors enter the building in conduit? 5', 10', 100'? I cant find anywhere in the Code that mentions distance so I am assuming that I can put the array disconnect in the Basement along with the inverter as long as the output conductors are in conduit, right?
Click to expand...

The 'remote' disco must be outside the building or "inside nearest the point of entrance of the system conductors" 690.14(C) 2011.
"Exception: Installations that comply with 690.31(E)" ...

690.31(E) has a few additional requirements besides simply being in conduit. It must be marked, not installed directly under the roof, etc.

Basically, you can put the disco anywhere inside as along as the wiring method complies with 690.31(E) from the point of entrance to the point of the disco.
 
J

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
Scratchbuilt said:
.... It's been an interesting (read: frustrating)project to say the least.
Click to expand...

No offense, but I would have refused the job from the outset. Hopefully your agreement with the client includes that he will pay whatever it costs and you not be responsible if it cannot pass inspection. :D
 
S

SolarPro

Senior Member
Location
Austin, TX
The inverter must be something like this:

http://www.gosolarcalifornia.ca.gov...ies/Sustain NRG Techs Sunergy 5000-70-240.pdf

It looks like it operates between roughly 70 and 100 Vdc. Since the voltage is so low, you wind up with relatively high currents on the dc side of the system.

As far as the dc disconnect is concerned, I'd look at using a 3-pole device that lets you dedicate one-third of the PV array capacity to each of the three poles. Something like this:

http://w3.usa.siemens.com/us/intern...hes/docs_Literature/SSFL-BLADE-1110_FINAL.pdf

It will be a special order part, but it will get you away from requiring a 200 A disco.

You will need two or three combiners to aggregate the PV source circuits into three PV output circuits. You might be able to use Midnite solar combiners with circuit breakers (rather than fuses) since this is a relatively low voltage application. They should have listed combiners that will accommodate two separate output circuits. I don't think I've ever seen a single listed combiner that provided three separate output circuits.
 
S

Scratchbuilt

Member
Location
Denver, CO
jaggedben said:
Yikes. Yet another reason to stay away from 'solar shingles', in my opinion.

Bill's question is also my first question.

Also, if the shingles are only 11.3VDC each, why not string together, say, 40?
Click to expand...


The design and one-line was already completed and submitted to the City so we just went with it. Regardless it will work either way.
 
S

SolarPro

Senior Member
Location
Austin, TX
This system was designed by Atlantis Energy Systems and we are installing it for our client.
Click to expand...

Simply matching the array to the inverter isn't the same as designing the systems, especially in this case. It sounds like to need to fill in a some gaps in the system design. Unfortunately, this application is so atypical that even veteran system designers would have a difficult time with it. Since this isn't your area of expertise, you might want to lean on the vendor to provide a more detailed design and parts list.
 
S

Scratchbuilt

Member
Location
Denver, CO
And this is why I am here asking people with more experience. I thought all of this was strange from the get go but i am glad to get some other opinions that back up my original thinking.
 
S

SolarPro

Senior Member
Location
Austin, TX
You have an interesting decision to make. You can reduce the costs associated with the installation by getting a refund for the Sunergy inverter and replacing it with one that will accommodate a higher voltage dc input. For example, you could design around 30 or 40 modules in series, which would reduce the number of source circuits to 4 or 3. Most 5 kW string inverters likely accommodate one of these options.

Unless something about the roof layout makes this option virtually impossible, I'm not sure why the system designer would have specified the Sunergy inverter. The dc voltage isn't really low enough to qualify as "safe." But it is low enough to significantly drive up conduit, conductor, combiner, fuse and disconnect costs.
 
Status
Not open for further replies.
Top