Is My New System Undersized?

[Eleceng1979]

As a data point this is inverter clipping...

https://pvoutput.org/intraday.jsp?id...&gs=0&da=1&m=0

look at the center of the green line...the flat plateau. And the rise of dc voltage due to maximum inverter output current. This is text book clipping...

[sensij]

As a data point this is inverter clipping...

https://pvoutput.org/intraday.jsp?id...&gs=0&da=1&m=0

look at the center of the green line...the flat plateau. And three rise of dc voltage due to maximum inverter output current. This is text book clipping...

Also a good example of how insignificant most clipping is. I'd ballpark the "loss" from that clipping to be 0.2 kWh, which is 0.24% of the daily total, maybe $0.04 of electricity if the cost is $0.20 / kWh.

[bcroe]

The over voltage problem is best avoided by keeping the inverters close to the meter (where the wire gets bigger).
Usually more efficient running higher voltage DC the distance, but not an option with micro inverters. Next thing
is running massive wire from the inverters to the meter, keep the drop below 1%. And of course get your PoCo to
keep their voltage within legal limits, good luck. Adjusting the inverter trip voltage can work, or use an autotransformer.

I had that problem here, with a 600' loop of AC feed wire + outrageous line voltage. My installer never even tried
to anticipate what the voltage would be; later said not to worry, occasional dropouts would reset automatically. My
view is make hay when the sun shines. Bruce Roe

[Eleceng1979]

QUOTE=sensij;n347242]

This is true if the #3 run is in raceway, cable, or in earth. Admittedly, it is unlikely, but if the run is in free air the ampacity is higher and would be OK for 96 A (notwithstanding problems caused by voltage drop/rise).
[/QUOTE]

Sensij, why do you always pick a fight? You are the reason I left this site for months. I come here to help others not to fight about trivial BS. The installation is plain wrong...no amount of gray area twisting and turning will change that fact nor the requirements of the code. If you spent the time to read the code fully and think about what I said I would leave well enough alone. Instead you find one Internet search of data to pick at me with. If your income does not come from practicing this work legally, with a license in good standing, with frequent inspections of your work maybe you stop engaging in topics like these. The AHJ/Inspector always wins... not me or you. I just prefer to be compliant...the conversation is always easier with all when you are. See you in a few months... keep telling all to lease solar with undersized wiring and crap grounding... I have more installs to quote, later.

You are wrong. Code requires conductor ampacity of the continous 96A load x 125% = 120 amps. #3 quadplex open air is 118 amps, then increase in size for length puts free air sizing closer to underground sizing due to voltage drop. Free air allows greater current flow but this also creates higher voltage loss per a given size of wire. Voltage drop is tolerable in a typical load...like a dryer or a subpanel in a garage. When generating power, voltage drop is lost revenue and the enemy. Nobody with a brain would sign up for 3% voltage drop prior to metering when generating power for a living. Free air, conduit, cable tray, etc... doesn't matter...ohms per foot does in a power gen application.

Factor in the requirement of a 125A subpanel buss, no 120A circuit breaker being available in a local supply house or made for that matter, places the wiring clearly above 125A due to the use of a 125A breaker protecting the subpanel. Factor in local ambient temp derate and distances and I see this even higher.

If you find inspectors or electricians arguing that a 125A requirement over 200' away on 96 or 118A wiring is acceptable they should be smacked.

if the electricians screwed up the wiring due to laziness did they screw up the grounding also? I got a buck that says yes... I predict a subpanel, on a detached building with no EGC and no rod driven. I also predict they drove a rod at the ground mount and didn't tie it into the sub panel or house ground system. While I am spit balling I bet they ran one EGC from the panels to the inverters and daisy chained it to all 3 inverters using seperate pieces of non-continous wire. All with an existing non dedicated solar panel with actual loads powering outlets and lighting. Take photos of all enclosures once de-energizied so we can see...

A wise inspector once told me that he judged entire projects initially from the installation of recptacles. If you don't take the time to do the easy mundane things correctly, you obviously wouldn't take time with the important stuff, then the probing began... moral of the story... I would question everything, call an independent inspector and go top to bottom then have a sit down with your solar installation company. An inspection might cost $150 or a bit more. Well worth the probing at this point.

PV4ME Sorry your install is a problem. It is rare to find quality people who do quality work for a fair price. My apologies for being a dick in this post. There is history previous and it doesn't involve you. Sorry your post is derailed with my ramblings. I hope you sort it all out

[sensij]

Ah, ok. Not sure where all that came from, but since this is an operating system that was presumably inspected by the AHJ and approved, I thought it might be worth considering ways what the OP wrote could be interpreted to be compliant with code. Maybe it was an error, maybe the plans submitted for permit check mis-represented the existing wiring and wasn't caught. Who knows? I'm not defending the installation, and what you spelled out looks like a good starting point for the OP to take back to his installer or an independent electrician or inspector.

J.P.M. I'd agree the stringing is unusual. The inverter has an operating range of 100-550 V, but a rated range of 270-480 V. The 185 Vmp of the 5 panel strings will work, but somewhat less efficiently. The inverter has 3 mppt inputs, seems like strings of 8, 8, and 9 into each inverter would have been more conventional. Hard to argue with the results though if everything is as the OP has written and he is seeing clipping.

[J.P.M.]

Ah, ok. Not sure where all that came from, but since this is an operating system that was presumably inspected by the AHJ and approved, I thought it might be worth considering ways what the OP wrote could be interpreted to be compliant with code. Maybe it was an error, maybe the plans submitted for permit check mis-represented the existing wiring and wasn't caught. Who knows? I'm not defending the installation, and what you spelled out looks like a good starting point for the OP to take back to his installer or an independent electrician or inspector.

J.P.M. I'd agree the stringing is unusual. The inverter has an operating range of 100-550 V, but a rated range of 270-480 V. The 185 Vmp of the 5 panel strings will work, but somewhat less efficiently. The inverter has 3 mppt inputs, seems like strings of 8, 8, and 9 into each inverter would have been more conventional. Hard to argue with the results though if everything is as the OP has written and he is seeing clipping.

The system is what it is, and none of us around here, except for the OP, have access to it, making better guesses as to WTF is going on impossible. We all know the inspector is always right, but that's not to say the inspector catches everything on a job. I've actually seen one/two jobs where the AHJ had his way with the pooch for who knows what reason(s)..

Not knocking the OP either. He came here looking for opinions and I'd guess hopefully some info and experiential insight, but what reads to me like a certain lack of background in electrical work and solar may be causing confusion and less than effective communication. What I read tends to make me wonder if a few corners might have been cut in ways we wouldn't do for our own systems and just maybe the AHJ didn't have his glasses as clean as possible that day.

[PV4Me]

Hello guys, wow this thread has blown up. I wanted to first of all say thank you to everyone who is contributing. I really do appreciate it!

This installer did come recommended from a few contractors in the area but I believe he may be out of his depth with the size of this install. He also was not even closest to the lowest bid, and seemed very confident about what he was doing until we started having issues.

The contract we signed stated that any permits that would be required were included in the final price and that it was the installer's responsibility, however after we signed and he had ordered the materials he stated that there was no need for any permit as we were simply upgrading the panels and inverters that were previously installed and so this would not constitute a new system or require any permits. He insisted that since I am grandfathered in with PG&E NEM 1.0 Solar (my electric company), that there was no need for a new permit.

The old system was comprised of 80x 130w GE panels and was installed in 2006. The #3 copper seemed to be no issue for that, and this installer measured the voltage drop from the array site to the MSP and stated that there was no drop and that his calculations stated that there should be no problem to do 96 amps on it. This is my major point of contention with him because I had done my own math and was not confident that it would work at all. We probably had this discussion 10 separate times and he kept telling me it would.

Well here we are now and hindsight is 20/20 and now he is stating that we definitely need to upgrade the wiring and that everything will work then. I just need to fork over another significant amount of cash to make it happen.

The installer's new proposal for wiring is:

400' 4/0 copper THHN for L1 L2
200' 2/0 copper THHN for N
2" EMT
200a outdoor rated sub panel

At this point I'm not sure what to do. His stance about not needing a permit is worrisome. He says since I already have a solar meter from the pre-existing solar setup, I don't need a permit with my utility company but that if I want to get permits with the county it will result in extra costs and delays. His contract reads: "The total contract amount includes the entire cost of the PV system including: profit, labor, materials, and permit costs." For the permit, he wants an additional $800 and another $300 for "plans and engineering costs".

I want the system working but these extra hurdles are making me wonder if the installer is qualified to do the work or not.

[J.P.M.]

Hello guys, wow this thread has blown up. I wanted to first of all say thank you to everyone who is contributing. I really do appreciate it!

This installer did come recommended from a few contractors in the area but I believe he may be out of his depth with the size of this install. He also was not even closest to the lowest bid, and seemed very confident about what he was doing until we started having issues.

The contract we signed stated that any permits that would be required were included in the final price and that it was the installer's responsibility, however after we signed and he had ordered the materials he stated that there was no need for any permit as we were simply upgrading the panels and inverters that were previously installed and so this would not constitute a new system or require any permits. He insisted that since I am grandfathered in with PG&E NEM 1.0 Solar (my electric company), that there was no need for a new permit.

The old system was comprised of 80x 130w GE panels and was installed in 2006. The #3 copper seemed to be no issue for that, and this installer measured the voltage drop from the array site to the MSP and stated that there was no drop and that his calculations stated that there should be no problem to do 96 amps on it. This is my major point of contention with him because I had done my own math and was not confident that it would work at all. We probably had this discussion 10 separate times and he kept telling me it would.

Well here we are now and hindsight is 20/20 and now he is stating that we definitely need to upgrade the wiring and that everything will work then. I just need to fork over another significant amount of cash to make it happen.

The installer's new proposal for wiring is:

400' 4/0 copper THHN for L1 L2
200' 2/0 copper THHN for N
2" EMT
200a outdoor rated sub panel

At this point I'm not sure what to do. His stance about not needing a permit is worrisome. He says since I already have a solar meter from the pre-existing solar setup, I don't need a permit with my utility company but that if I want to get permits with the county it will result in extra costs and delays. His contract reads: "The total contract amount includes the entire cost of the PV system including: profit, labor, materials, and permit costs." For the permit, he wants an additional $800 and another $300 for "plans and engineering costs".

I want the system working but these extra hurdles are making me wonder if the installer is qualified to do the work or not.

If I was you, I'd consider lawyering up, or at least seek a legal opinion. You may also want to consider limiting further discussion about this subject in the public arena. Reasn: Your vendor may well have access to this forum. Just sayin'.

I believe you needed a permit, design review and inspection. I also believe that PG & E has limits on how much a system size can be increased without changing the NEM agreement. This is turning into something like a septic tank where the big chunks eventually float to the top.

FWIW, from what you write, it sounds like you may be dealing with a less than reputable vendor. I'll say no more.

[sensij]

While you consider your longer term strategy, some ideas to consider in the short run:

1) Get access to your inverters before your relationship with your installer deteriorates further. If you haven't been shown how to log into them, try asking.
2) To eleceng1979's point about the rating of the 3 AWG, look for a way to limit the combined inverter output to <19.2 kW (80 A). If you can't get access to the inverters to set a limit, then shut one of them down.
3) Further to his point, and especially since your system most definitely needed a permit, inspection, and PG&E authorization of the change to be compliant... get a 3rd party to come in an look over everything, or shut it down completely.
4) You may have problems with PG&E if you try to run more than your interconnect agreement allows (10.4 kW) and they detect the unauthorized increase in backfeed. For that reason, if you choose to continue to operate, you could shut down two inverters, or at least limit the combined output to 10.4 kW.

Just replacing the #3 wire does not solve your problems. The original system still would have had 1.4% loss at peak output, and I'm not buying that the additional 1.7% loss is solely responsible for voltage problems you are seeing. Something else isn't right, and you might need to get PG&E involved to figure it out.

[PV4Me]

Hello all,

Another update. Met with the installer and went over all of my concerns regarding permits and inspections as well as the system not working as designed and he was very receptive to my concerns.

He is getting started on the permit process with the county office and has agreed to do everything to the specifications that would pass inspection. He strongly believes that the wiring is the sole cause of all my troubles and that running a larger wire will get me up and running.

He proposes using the following for the 200' run:

400' 4/0 copper THHN for L1 L2
200' 2/0 copper THHN for Neutral
2" EMT conduit
200a outdoor rated sub panel

Regarding the string configuration, I am not sure what the logic is behind how he currently set it up with 10 panels on the first 2 strings and 5 panels on the third string. It seems like the 8/8/9 configuration would be a better setup. I will ask him more about this but if the answer is "trust me", should I ask him to rewire it to be a more conventional arrangement? It makes sense that the 5 panels on the third string will not be in the rated range of 270-480 V if the voltage max power is 185.

Reading more about this stuff and learning a lot. Thank you again everyone, I really appreciate you taking the time to read and reply.

[PV4Me]

I used the SMA Sunny Boy design tool and the string configuration which it recommends doesn't make sense to me.

I'm attaching the screenshot of what it recommended but here is the summary:

Inverter 1:
A: 1 x 11
B: 1 x 11
C: 1 x 5

Inverter 2:
A: 1 x 11
B: 1 x 11

Inverter 3:
A: 1 x 11
B: 1 x 11
C: 1 x 4

Any idea why it would recommend this sort of configuration?

Inverter Recommendation.png

[J.P.M.]

Hello all,

Another update. Met with the installer and went over all of my concerns regarding permits and inspections as well as the system not working as designed and he was very receptive to my concerns.

He is getting started on the permit process with the county office and has agreed to do everything to the specifications that would pass inspection. He strongly believes that the wiring is the sole cause of all my troubles and that running a larger wire will get me up and running.

He proposes using the following for the 200' run:

400' 4/0 copper THHN for L1 L2
200' 2/0 copper THHN for Neutral
2" EMT conduit
200a outdoor rated sub panel

Regarding the string configuration, I am not sure what the logic is behind how he currently set it up with 10 panels on the first 2 strings and 5 panels on the third string. It seems like the 8/8/9 configuration would be a better setup. I will ask him more about this but if the answer is "trust me", should I ask him to rewire it to be a more conventional arrangement? It makes sense that the 5 panels on the third string will not be in the rated range of 270-480 V if the voltage max power is 185.

Reading more about this stuff and learning a lot. Thank you again everyone, I really appreciate you taking the time to read and reply.

NOMB, but you still trust this guy ? Dovetailing off Sensij's comments, I'd either get another technical opinion from a true solar professional, and pay for the advice if necessary, or take a crash course in solar PV technology, or better yet, both. In the mean time, if you mean to keep him, I'd watch the vendor like a hawk and question everything he says and does.

Even if well intentioned (??), it sure sounds like he got you into some problems if only out of ignorance. Given what you've written, and not knowing anything else, and again dovetailing off Sensij, I'd have some safety concerns about what's been done and consider shutting down the entire array until things get squared away. In the mean time, fess up with PG & E beaucoup pronto. They'll find out anyway.

[PV4Me]

Thank you J.P.M.

I definitely want to have everything be 100% compliant and will be contacting PG&E. My feeling is that having an inspector involved will keep everyone on their toes, but I am also looking into getting another technical opinion. The installer is really willing to work with me to get stuff up to code so at this point I am moving forward with him but I am trying my best to be cautious and observant.

It is a bit of a conflicting situation because I don't believe there is any malevolence on the installer's part, he just is/was out of his depth and his fundamental understanding of electrical theory is somewhat weak. But that being said he has installed systems for other people I know and they have had no issues with him or his work, but their installs were about 25% the size of the setup I am trying to achieve.

I do have login access to the inverters and actually did the initial setup on them so that's not an issue. Because the inverters were so far from the house, my home's wifi signal didn't reach out there and so the installer wasn't able to configure the inverters until I put a Point-to-Point wifi antenna out there.

This is definitely a learning experience!

[bcroe]

Keep in mind, the big wire will only reduce line voltage at the inverters a few volts, some fraction of the current
rise. The voltage at your meter will be just as high, might even rise a tad from the increased efficiency. The best
fix is get your PoCo to lower the line voltage; otherwise your investment is being wasted. Bruce Roe

[sensij]

I used the SMA Sunny Boy design tool and the string configuration which it recommends doesn't make sense to me.

Any idea why it would recommend this sort of configuration?

Not really. You could try forcing the design to what you actually have (10, 10, 5 on each inverter), as well as the more balanced (8, 8, 9) and see if there are any differences in the software output. I don't think the stringing design is worth messing with. The installers choice might have been based on what minimizes the length of wire, which is a reasonable factor to consider... in other words, 8, 8, 9 is not better if it means a lot more PV wire is required to get all of the strings to the junction box for the run to the inverter.

The real problem I'd have at this point is that when you've been given such bad information about the permitting and interconnection requirements, as well as basic wire sizing problems, it is hard to know what else was done wrong. It isn't reasonable to expect an AHJ to catch all of the potential shortcuts an installer could take, there needs to be a minimum level of professionalism and trust that it sounds like your installer has failed to meet.

From the PG&E standpoint, my understanding is that the capacity of your original array will continue to be on NEM 1.0, while the increased capacity will be on NEM 2.0. I don't have any idea how their billing software will accommodate an arrangement like that. I hope that you continue to post your experiences here, since the idea of increasing the size of the array a few years later is often kicked around, but the real-world experience and consequences of that are hard to come by.