The good news is that the fundamentals remain the same as you scale up. I would think that the biggest concern would be interconnecting at medium voltage; MV is a whole new ball game.Does anyone have recommendations for books or other resources for gaining more knowledge in the areas of transformer design, protection, duct banks, and switchgear as it pertains to designing large solar PV systems, like in the 1MW to 10MW range? I have a lot of experience with smaller systems, but not large systems like this. Thank you in advance for any guidance.
There are quite a few inverters now that have 600VAC or 800VAC output. To use one of these for a behind the meter application that has 480V service, would require a 800:480V transformer. Even this is a different ballgame, let alone MV. The higher voltage would enable smaller conductors, smaller duct bank, and/or have less voltage drop, but would the cost of the transformer make it cost prohibitive? Also, things like combiners and switches would need to be rated for 800V. I am trying to understand better the tradeoffs and design details and practical challenges in these larger systems, that really don't come up in the commercial or residential systems.The good news is that the fundamentals remain the same as you scale up. I would think that the biggest concern would be interconnecting at medium voltage; MV is a whole new ball game.
Thanks for the info, I will check out Maddox. I can't jump into the pool and get hired by someone. I have my own company and work for myself, and don't want to go back to working for others. Also, I have been studying off and on to get my PE, and need to just knuckle down for a few months and get to a point where I can take the test. That helps a bit. I found a course on Heatspring that might be worth taking, not sure if that was what you are referring to. The course is https://www.heatspring.com/courses/interconnection-of-utility-scale-solar-pv-to-distribution. I think I am going to buy ampcalc finally. Also, I need to renew my NABCEP PVIP before the end of the year, so hopefully I can find some courses that will apply to both needs. Large scale to me is around 1MW and up.I do not know of any resource like this. Large scale PV, BESS, and wind design are a lot like HV substation design. People learn how to do these by joining a firm that does it and get trained on the job. There are training programs advertized to train people to do large PV design but after looking over the course material they are really teaching how to do larger commercial PV.
What you can do to learn more about the components is to go to manufacturer websites and look for training material there. Many manufacturers have guides that teach about designing with MV Xfmrs and SWBDs for instance. It's not PV specific but gives a general background. Maddox Transformer for instance has great videos on how MV xfmers work and how to design with them. Eaton, Square D, and others have training material.
But to learn large scale design specific to PV you just have to jump into the pool by getting hired by a company that does this work and learning on the job. Also the size that is considered "large scale" has continued to increase over the years. When I started a large scale PV system was 500kW. Today anything below 50MW is not really considered large scale.
I don't think many (any?) utility scale PV systems interconnect at 480V; such a system's output could be several thousand amps at that voltage. The inverters that have 600V output are intended for MV interconnection through a transformer.There are quite a few inverters now that have 600VAC or 800VAC output. To use one of these for a behind the meter application that has 480V service, would require a 800:480V transformer. Even this is a different ballgame, let alone MV. The higher voltage would enable smaller conductors, smaller duct bank, and/or have less voltage drop, but would the cost of the transformer make it cost prohibitive? Also, things like combiners and switches would need to be rated for 800V. I am trying to understand better the tradeoffs and design details and practical challenges in these larger systems, that really don't come up in the commercial or residential systems.
I agree on the voltage. It is not ideal. However in this case we have a large customer on an adjacent property that will be the off-taker for the first phase of this project. The system will be behind their meter. And as of right now it is metered after the 480V transformer. I am comfortable with scaling up all the fundamentals, the gap/questions I have is being confident in the details of designing the interconnection path after the inverter, understanding better what to look for in and talk to in the utility equipment in the service feeder, etc. I am getting involved more with larger projects like this. I just want to up my game in this knowledge. I plan to sit for my PE exam soon as well.I don't think many (any?) utility scale PV systems interconnect at 480V; such a system's output could be several thousand amps at that voltage. The inverters that have 600V output are intended for MV interconnection through a transformer.
Design on the DC side of utility scale PV is pretty much the same as it is at any other scale; the fundamentals (wire sizing, OCPD, etc.) scale up well. Even with 600V inverter output on the AC side, individual inverter to AC combiner design is pretty much the same as it ever was. Beyond that, however, is where things get very different.
How many kW AC is the system? It might be cheaper to use 480V native inverters than to design it with 600V inverter(s) and a transformer.I agree on the voltage. It is not ideal. However in this case we have a large customer on an adjacent property that will be the off-taker for the first phase of this project. The system will be behind their meter. And as of right now it is metered after the 480V transformer. I am comfortable with scaling up all the fundamentals, the gap/questions I have is being confident in the details of designing the interconnection path after the inverter, understanding better what to look for in and talk to in the utility equipment in the service feeder, etc. I am getting involved more with larger projects like this. I just want to up my game in this knowledge. I plan to sit for my PE exam soon as well.
Most likely 1.5MW, to keep it under the size needed to safe harbor using the old 5% purchased equipment rule. I think your suggestion and the question about what the POCO may want is all good and relevant to my initial ask about how best to become more knowledgeable in these details, so I can better understand the tradeoffs. Like at what point does the cost and efficiency of transformers look better than many parallel long paths of conductors in duct banks. And what are the likely extra details a POCO might want included, what are the cost and lead times? I think I am going to take that Heatspring course, look at some distribution equipment manufacturers and what videos and training materials they have, and refocus on finishing my study for the PE, which touched on a lot of this stuff. But any additional suggestions are welcomed. Thank you for your input.How many kW AC is the system? It might be cheaper to use 480V native inverters than to design it with 600V inverter(s) and a transformer.
The POCO might want you to install gear that would give them access to and control of the system. I ran into that a couple of times and I had to get help with it.
My project was over a MW, but unfortunately I do not have it on my computer any more. I used a bank of 480V inverters on the roof (it was a huge building) with the combiner inside right below them, and the MDP for the facility was right next to it, so the AC conductors were not all that long. The system was supply side interconnected, and the POCO required an SEL unit with a cell connection and a shunt trip disconnect so they could control and monitor the system; that's the part I needed help with.Most likely 1.5MW, to keep it under the size needed to safe harbor using the old 5% purchased equipment rule. I think your suggestion and the question about what the POCO may want is all good and relevant to my initial ask about how best to become more knowledgeable in these details, so I can better understand the tradeoffs. Like at what point does the cost and efficiency of transformers look better than many parallel long paths of conductors in duct banks. And what are the likely extra details a POCO might want included, what are the cost and lead times? I think I am going to take that Heatspring course, look at some distribution equipment manufacturers and what videos and training materials they have, and refocus on finishing my study for the PE, which touched on a lot of this stuff. But any additional suggestions are welcomed. Thank you for your input.
Lol, you just taught me something. I looked up what an SEL unit is.My project was over a MW, but unfortunately I do not have it on my computer any more. I used a bank of 480V inverters on the roof (it was a huge building) with the combiner inside right below them, and the MDP for the facility was right next to it, so the AC conductors were not all that long. The system was supply side interconnected, and the POCO required an SEL unit with a cell connection and a shunt trip disconnect so they could control and monitor the system; that's the part I needed help with.
Programming an SEL is a non-trivial exercise.Lol, you just taught me something. I looked up what an SEL unit is.
