Commericial Solar Interconnection

[andrew.tkelly]

Hi everyone,

I'm PV systems designer. I've designed hundreds of small and large residential arrays, as well as some small commercial arrays, but I want to grow my knowledge in interconnecting large commercial arrays. My academic background is in electronic materials engineering, so in the past year and a half I've had to learn all my residential interconnection knowledge from our company's electrical journeymen. Most of the electricians we have working for us are skilled in residential, but not as much in commercial. Things like switchgears are intimidating to even look at, but I'd like to become more familiar with the components, and especially the design parameters involved with them. Does anyone have any good websites or books to recommend?

Thank you.

Kind Regards,
Andy

 

[ggunn]

Hi everyone,

I'm PV systems designer. I've designed hundreds of small and large residential arrays, as well as some small commercial arrays, but I want to grow my knowledge in interconnecting large commercial arrays. My academic background is in electronic materials engineering, so in the past year and a half I've had to learn all my residential interconnection knowledge from our company's electrical journeymen. Most of the electricians we have working for us are skilled in residential, but not as much in commercial. Things like switchgears are intimidating to even look at, but I'd like to become more familiar with the components, and especially the design parameters involved with them. Does anyone have any good websites or books to recommend?

Thank you.

Kind Regards,
Andy

Good luck in your quest. I asked the same question when I began delving into commercial PV design, but I really didn't find many useful answers. My best resource has been the experienced master electricians I have worked with. I still don't know much about medium voltage interconnection, although I have worked with some pretty big 480V MDP's now.

 

[AaronWood2008]

Google anything related to NABCEP training and that will put you in the right direction.

 

[electrofelon]

Hi everyone,

I'm PV systems designer. I've designed hundreds of small and large residential arrays, as well as some small commercial arrays, but I want to grow my knowledge in interconnecting large commercial arrays. My academic background is in electronic materials engineering, so in the past year and a half I've had to learn all my residential interconnection knowledge from our company's electrical journeymen. Most of the electricians we have working for us are skilled in residential, but not as much in commercial. Things like switchgears are intimidating to even look at, but I'd like to become more familiar with the components, and especially the design parameters involved with them. Does anyone have any good websites or books to recommend?

Thank you.

Kind Regards,
Andy

Hi Andy. IMO there isnt really much difference between a large solar system or electrical service, and small ones. I will give the disclaimer that I have been an electrical contractor for quite a while now so maybe I am "over easying it." I do remember in my earlier days being really intimidated by big stuff and thinking "there is now way I could do that"., however in hindsight, there isnt really anything different, just typically more sets of conductors and larger breakers - more inverters. Above 1000-1200 Amps you will typically be dealing with switchboards and not panelboards, but there is very little practical difference. IMO the thing I constantly find lacking in solar designers is they dont have much of an idea about installing this stuff and make it hard to install, use inefficient wiring methods, scatter equipment throughout the array, etc. It sure looks all neat and tidy on paper......Maybe you could arrange to get a tour of a large array or two? I think you would not find anything earth shatteringly different going on. Good luck!

 

[pv_n00b]

Making the transition from doing simple 240/120V interconnections to larger systems takes careful study. Pretty much all 240/120V services look the same. Larger systems, 3 phase, over 400A, no longer look the same. Large switchboards are commonly customized for each job so the box may look the same on the outside but what's inside is pretty variable. To learn how to do the interconnections you have to learn from someone who knows how to do it. It's really hard to pick up on your own unless you already have experience with commercial electrical system design.

Most AHJs require an electrical engineer to design and seal the electrical drawings for larger projects. Take that as an opportunity to work with an engineer and learn from them about interconnecting larger systems. Most engineers are more than happy to discuss what to look for, what the traps are, and how to design these interconnections. Take advantage of the opportunity to learn from others. Learning from electricians who are familiar with commercial system installation is also very useful. Engineers and electricians have experience in different areas that when brought together make a better system design.

Good luck.

 

[jaggedben]

I am about to deal with my first project (53kW) that fits the question, having done hundreds of residential but never having worked on a system this size except as an underling.

I figure I'll have to involve an electrician who is not on our regular staff. So that's definitely one difference.

Otherwise, the biggest difference I'm preparing for is in the longer lead times and extra steps I expect will required everywhere along the way. I mayneed multiple visits to determine the electrical configuration; an initial visit to find out what's involved, perhaps followed by another visit when a shutoff will not be too inconvenient for the customer. Whatever the electrician needs to do, breakers and components are likely to be special order and require that extra lead time.

 

[zman990]

NABCEP the trick test I am ready for results all ready.
I have found that talking with your local jurisdiction especially if you can talk about your plan with plans reviewer is a huge help.
Also envolving the local distributors and manufacturer of the gear is a huge help.
Local distributors in all my cases remember selling the equipment you will now be backing feeding with the sun.
If I don't feel comfortable touching the gear I won't touch it. Thinking about not feeling comfortable is an accident waiting to happen safety first.
Manufacturer would tell you don't open the gear without shutting the power off in most all cases.
Ask the main person at the distributor to come out and tell you what you are working with and have that person teach you about that specific gear it is just a bus and breakers
The distributor after all wants to make money,they will open it.
Also the equipment like disconnect and combiner panels and transformers are bigger and probably not sitting on the shelf.
So plan on buying some equipment with a new distributor every time you ask gear specific local distributors for help.
All major brands have lots of information on websites and Google is an amazing resource as always it is our new library.
Also finding the best electrician in town is of course very important but always use free resources first and get a plan before paying for a master electrician.
Product takes forever I am currently still waiting for a quote for 800 amp disconnect and 800 amp load center and transformers lead time is scaring me.
It would be a good idea to at least size the amperage of job and get the equipment you absolutely know u will need from to inverter and transformer asap.
Tie in is obviously very important but making sure your volts are in acceptable ranges when you get to the gear is acceptable.
I have not gotten the opportunity to put my skills to the test on large scale project meaning over 100kw but I am very confident I am ready seen a lot of gear in town 2016 is going to be a massive year.
Again I can not stress the transformer lead time enough.....
Have fun powering America one solar panel at a time..




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[electrofelon]

Making the transition from doing simple 240/120V interconnections to larger systems takes careful study. Pretty much all 240/120V services look the same. Larger systems, 3 phase, over 400A, no longer look the same. Large switchboards are commonly customized for each job so the box may look the same on the outside but what's inside is pretty variable. To learn how to do the interconnections you have to learn from someone who knows how to do it. It's really hard to pick up on your own unless you already have experience with commercial electrical system design.

I would disagree a bit There is nothing different going on in a 2000 amp switchboard. Its all the same rules. It can be intimidating at first but just remember, its all the same rules and the same parts - You will have service entrance conductors and/or busing and between 1 and 6 service disconnects. You will be doing a supply side connection or a load side connection. The one thing that can be a bit sticky is landing lugs on the service busing for a supply side connection, but there still isnt any "experience" to it - you are going to have to find lugs/connectors that fit, get the blessing from you inspector or manufacturer to drill the busing, or see if by chance the manufacturer offers another solution. Dont worry about knowing gear in terms of what the max size square D QMB switch that you can fit in a 42" cabinet is or what strap kit you need for a siemens P4 panelboard - that is what the gear guy at the supply house is for. All that said, you would need an electrician with commercial experience to do commercial work of course.

honestly, I have been disappointed after doing many larger systems. My first large system was 1 meg followed by 9-10 350 KW. After the second day on the 1 meg system, I realized
i could have designed that no problem (and better and cheaper than the guy who did design it). I thought it would be cooler, more interesting,challenging but it is just the same thing with more inverters.

 

[shortcircuit2]

Not all switchboards have fully rated bussing throughout the switchboard. Consideration would need to be given to a load-side connection in a switchboard section with reduced rated bus downstream of the main. These connections need to be designed under engineering supervision.

 

[jaggedben]

I would disagree a bit There is nothing different going on in a 2000 amp switchboard. Its all the same rules. It can be intimidating at first but just remember, its all the same rules and the same parts - You will have service entrance conductors and/or busing and between 1 and 6 service disconnects. You will be doing a supply side connection or a load side connection. ....

I think what PV n00b was saying was that if you're only familiar with 100 and 200A panelboards then dealing with the actual parts for larger amp system may be intimidating. You're not going to find that 500A amp breaker at Home Depot, for example. If you're used to blazing through a residential install in 5 hours and you always just show up with your jumbled collection of $5-$20 breakers of multiple brands, and you didn't even know what you needed until you got there but it didn't matter, and this works for you nine times out of ten... Well, you're going to need to be adaptable to a somewhat different mindset to install larger commercial interconnections.

Or to put it more succinctly, we have residential electricians and commercial electricians and not everyone crosses over easily.

I suppose I'm drifting a bit from the point... For a designer, yes, the concepts are all the same and it makes no real difference. But I have to say that I've seen enough designs on residential systems from designers who clearly had never installed a circuit breaker of any size. I would say that one can be a 'competent' designer at any level in the sense of knowing the code and drafting a code compliant design, but this does not ensure your design will be practical for the person who actually has to obtain the materials and install them. At the commercial level such knowledge gaps are going to be more financially important.

I also have to say that 120/240V services are not pretty much all the same. After 4 years of looking at dozens per month I still get regular surprises.

 

[electrofelon]

Not all switchboards have fully rated bussing throughout the switchboard. Consideration would need to be given to a load-side connection in a switchboard section with reduced rated bus downstream of the main. These connections need to be designed under engineering supervision.

While it is true and a good point you make that a distribution section of a switchboard may have a lower rating than the service section, I dont see needing an engineers involvement in general. Can you point to any NEC rules that would require/allow engineering supervision in these cases? I am not aware of any. Each section should be clearly labeled with the rating of that section

I also have to say that 120/240V services are not pretty much all the same. After 4 years of looking at dozens per month I still get regular surprises.

That is very true. Much higher potential for the brother-in-law factor with resi than with a 2000 amp 277/480

 

[jaggedben]

While it is true and a good point you make that a distribution section of a switchboard may have a lower rating than the service section, I dont see needing an engineers involvement in general. Can you point to any NEC rules that would require/allow engineering supervision in these cases? I am not aware of any. Each section should be clearly labeled with the rating of that section

705.12(D) says something about engineering supervision for multiple ampacity busbars. Same as with centerfed busbars. I guess the question might be what the term 'multiple ampacity' properly applies to.

That is very true. Much higher potential for the brother-in-law factor with resi than with a 2000 amp 277/480

LOL. Exactly.

 

[shortcircuit2]

705.12(D)(2)(3)(d) on the engineering supervision with fault studies and busbar load calculation.

 

[shortcircuit2]

Anyone been involved in a larger commercial loadside connection to a switchboard with multiple amp rated bussing? How did the job work out?

Lets say for example you have a 2000amp 120/208 service which has a 2000amp main horizontal bus and a section with 1200amp vertical bus that has room for a loadside connection. The section with the 1200amp bus has existing load calculated at 800amp and the 125% PV input is 340amps requiring 350 OCP. Is this doable? It would appear to be OK...but requires engineering to support the connection right?

 

[jaggedben]

Lets say for example you have a 2000amp 120/208 service which has a 2000amp main horizontal bus and a section with 1200amp vertical bus that has room for a loadside connection. The section with the 1200amp bus has existing load calculated at 800amp and the 125% PV input is 340amps requiring 350 OCP. Is this doable? It would appear to be OK...but requires engineering to support the connection right?

I think you need to tell us something about how each bussing section is protected on the utility end.

 

[shortcircuit2]

I think you need to tell us something about how each bussing section is protected on the utility end.

By the 2000amp Main...

 

[jaggedben]

I agree that would require engineering supervision. The code is pretty clear on it.

 

[electrofelon]

Anyone been involved in a larger commercial loadside connection to a switchboard with multiple amp rated bussing? How did the job work out?

Lets say for example you have a 2000amp 120/208 service which has a 2000amp main horizontal bus and a section with 1200amp vertical bus that has room for a loadside connection. The section with the 1200amp bus has existing load calculated at 800amp and the 125% PV input is 340amps requiring 350 OCP. Is this doable? It would appear to be OK...but requires engineering to support the connection right?

Yes that is an interesting scenario. You are screwed right out of the gate on the 120% rule, and cant use 705.12(D)(2)(3)(c). I have never done a load side on a switchboard, they have all been an additional "main" or lugging onto the service busbars.

 

[BillK-AZ]

Another item that is different is dealing with ground fault protection and the suitability of breakers for backfeed. This usually requires a professional engineer to seal the plans for the permit.

 

[electrofelon]

Ok all fair points but we can come up with all sorts of scenarios that require engineering support or result in great difficulties for an interconnect. There is and always will be oddball stuff and challenging situations. I hold to my thesis in post #4 that most of the time, there is nothing generally challenging about connecting to large services/switchboards most of the time. Every switchboard connection I have done or been involved with was straightforward.