Newbie here doing a 20.8kW DYI install (80 sunMAX 260W panels with microinverters)

[foo1bar]

Had 6 inverters drop out today and they will stay down until they see the line voltage drop below something like 245V I think, so that likely means they won't be back online until tomorrow morning.

Turn on a few giant resistive heaters to warm up the shop and see if that reduces the voltage enough that they can come back online.
(or if you don't have heaters, but have a number of halogen lights, a bunch of those would have similar effect (and add some heat to the shop too).

[pclausen]

Thanks for that link! I'm surprised I didn't see that before when I went looking. I did reach out to them and they are willing to reprogram my inverters to a higher upper limit, but they want a letter from my POCO first stating they are ok with it. This way Ubiquiti are not liable if something goes wrong. They have run into that before. I have a note into the POCO explaining the situation and requesting a letter. We'll see how they respond.

Once I get my sense power monitor online, I should be able to better track what is happening on the line side and see if there any any major power fluctuations.

[FNG AZ]

https://help.ubnt.com/hc/en-us/artic...rror-Codes-#ac frequency discontinuity

Maybe you had a power bump?

[pclausen]

Had 6 inverters drop out today and they will stay down until they see the line voltage drop below something like 245V I think, so that likely means they won't be back online until tomorrow morning.



I'm going to open another dialogue with sunMAX/Ubiquiti about modifying the thresholds. They indicated previously that it would not be difficult, but that they were not allowed to due to UL requirements for North America. They sell these inverters worldwide and they are programmed differently based on the region they are deployed in. I think the parameters are all stored in the solar gateway and pushed out to the inverters from there. That's how I upgraded the firmware on them all when I first got them online and realized they were running pre-release BLE firmware.

[bcroe]

maybe it's time for a pair of 480V transformers for your local run? Does Iron cost less than
copper? But then you have all the internal losses in the transformers....

Yes that works. But now you have the losses of 2 transformers, instead of the single stage auto transformer. And you are transforming
100% of the energy instead of an adequate small percentage. Maybe 20 times the losses. Not to mention space and cost, perhaps
10 times as powerful, and at both ends instead of just one. Bruce Roe

[Mike90250]

maybe it's time for a pair of 480V transformers for your local run? Does Iron cost less than copper ? But then you have all the internal losses in the transformers....
Are you served with a nearby pole with a 6KV transformer ? How far have they run the 240V wires? Out here, remote houses get their own local transformer

[bcroe]

OK, the other part of the puzzle is what the Indiana Administrative Code says the nominal voltage set point may be. Seems like it shouldn't
exceed 120V or 240V. Then 6 % tolerance, but setting it at 125V will surely cause peaks above that level at times.

As SunEagle says, the PV grid tie inverters have pretty strict requirements to stay on line. If the PoCo is going to operate this way, it appears
the requirements need some relaxation or adjustment to suit the real world. The concept that the max inverter output voltage must be tightly
restrained is certainly debatable; for residential PV the inverter CANNOT set the line voltage, only react to it. SunEagle solved his problem
by reprogramming the inverter. At one point it appeared high line combined with V rise in my wiring would shut me down; fortunately here the
inverters had 277V operational capability. I must admit, the high line is now letting me run more voltage and less current, lowering my AC
losses in a 600' loop. But reprogramming dozens of micro inverters is a big job; is it even possible? Bruce Roe

[pclausen]

In my case, my POCO is a small rural co-op with 35k members. They have 4,700 miles of line with an average of 8 meters per mile and about 30 substations total. They told me they like to set the voltage to 125V for each leg to neutral at the substations, to ensure that customers at the end of each line receive at least 120V. I'm 3.7 miles (straight line) from my substation, so that is probably more like 5 miles actual.

240V + 5% = 252V, so being at 247V on average means I'm within code by most standards. I have 200' of MCM500 cable between the shop and the house meter base, so that keeps the voltage drop there to a minimum. However, I have a 220' run of 350MCM from my meter base to the transformer on the pole that is the property of the POCO. I have a potential for generating 20kW during optimal conditions. So that's a 1.3V drop from the pole to the meter base, in addition to whatever drop I have between the meter base at the house and the microinverters at the shop. I can't do anything about the 220' run between the meter base and the pole, and the total path from the microinverters back to the meter base is optimized as much as it can be I think:

Microinverter String
|
45' #10Cu
|
Shop Sub-Panel
|
4' 3/0Cu
|
Shop Meter Base
|
200' MCM500Al
|
Splice
|
5' MCM300Cu
|
400A disconnect
|
5' MCM300Cu
|
Meter Base

I'll be receiving my solar Sense (sense.com) power monitor tomorrow, so I'll be able to monitor everything going forward, tracking utility line voltage, consumption and generation. So I'll be able to document any issues and present them to the POCO. The POCO is very friendly and go out of their way to assist their 130 and counting solar customers. I was at a meeting hosted by the POCO a few weeks back, and about 100 of the 130 solar customers were present.

[DanS26]

When I was designing my PV ground mount system, I was very much attracted to the micro-inverter setup. Mainly because of the panel level monitoring. During my research the Enphase documentation constantly warned of the voltage drop (rise) problem if the inverters were located far from the main service entrance. Because I had a TED system monitoring my electrical usage, I also knew that I had high average voltage from the POCO.......same issue now faced by the OP.

My solution was to design a dual string inverter system, which although was a compromise on individual panel monitoring, gave me the flexibility to deal with the high voltage problem. By locating the string inverters close to service entrance I was able to mitigate the voltage rise problem. By having dual string inverters, I know immediately if a panel goes bad.......I just don't know which one unless I investigate further. Here's how.......if one inverter starts under producing, I now know which set of strings is involved.....then I compare those strings and narrow the problem down to 12 of the 72 panels......then I find the problem panel. Simple and effective.

[DanS26]

That is true, but there ARE regulations. Changing the operating point tap is a different issue than regulation/fluctuations. Bruce Roe

Here is what the Indiana Administrative Code says about permissible voltage variation.........

170 IAC 4-1-20 Standard nominal service voltage; permissible voltage variation
Authority: IC 8-1-1-3; IC 8-1-2-4
Affected: IC 8-1-2-33
Sec. 20. Standard Voltage and Permissible Voltage Variation. (A) Each public utility shall adopt a standard nominal service
voltage, or standard nominal service voltages, as may be required by its distribution system for its entire constant voltage service,
or for each of the several districts into which the systems may be divided, and shall file with the commission a statement as to the
standard nominal voltages adopted. The voltage maintained at the customer's main service terminals shall be reasonably constant,
as follows:
(1) For residential service, the voltage shall be within five percent (5%) plus or minus of the standard adopted, and the total
variation of voltage from minimum to maximum shall not exceed six percent (6%) of the average voltage in cities and other
incorporated places having a population in excess of 2,500, nor eight percent (8%) of the average voltage in all other places.
(2) A greater variation of voltage than specified above may be allowed when service is supplied directly from a transmission
line, or in a limited or extended area where customers are widely scattered or the loads served do not justify close voltage
regulation. In such cases the best voltage regulation should be provided that is practicable under the circumstances.
(B) Variations in voltage in excess of those specified, caused by (1) the operation of power apparatus on the customer's
premises which necessarily requires large starting current, (2) the action of the elements, and (3) the infrequent and unavoidable
fluctuations of short duration due to station operation, shall not be considered a violation of this rule. (Indiana Utility Regulatory
Commission; No. 33629: Standards of Service For Electrical Utilities Rule 18; filed Mar 10, 1976, 9:10 am: Rules and Regs. 1977,
p. 354; readopted filed Jul 11, 2001, 4:30 p.m.: 24 IR 4233; readopted filed Apr 24, 2007, 8:21 a.m.: 20070509-IR-
170070147RFA; readopted filed Aug 2, 2013, 2:16 p.m.: 20130828-IR-170130227RFA

[SunEagle]

That is true, but there ARE regulations. Changing the operating point tap is a different issue than regulation/fluctuations. Bruce Roe

Yeah. The POCO has to keep the grid as stable as possible. Of course they can make a claim the problem is not theirs if there are customers on the line causing the issue.

Did I every tell you the story about a waste water treatment plant at the end of the line that was causing a phase angle issue which kept causing a 1 MW solar array at a high school to keep going off line every time they started a couple of their big motors?

We couldn't get their plant to fix the problem but we got the Inverter manufacturer to adjust the anit-island software to be less sensitive and ignore the phase angle issue for 20 more cycles before is shut down. We succeeded but the POCO only raised their hands and said they couldn't do a thing to help. Again they were not very helpful since the school was a 1MW co-generator.

[bcroe]

That is true, but there ARE regulations. Changing the operating point tap is a different issue than regulation/fluctuations. Bruce Roe

[SunEagle]

There are standards for line voltage; you might want to investigate and then push back harder.

An autotransformer would work, but its a clumsy solution. For openers it needs to be double ended, because if you try to
make an adjustment on just one line, your inverters might still trip out over the imbalance. If say you reduced 250V to 230V,
the shift of 20V represents 8% and the auto transformer size must be rated proportionally, not trivial at this power level. The
auto might have losses on the order of 1 to 5%, depending on quality. So that looks like losing 1/3% of the peak power, but
since it will be on continuously, day, night, rain, etc the overall losses could run well over 1% of generation. Size it too
big, losses go up; too small, it burns up.

A better way out is reprogram the limits of your inverters, a lot easier if running strings. This in fact is not really so different
from the auto transformer; the inverters now put out the same voltage the auto transformer would have. Bruce Roe

It gets hard to be a co-generator. Now you have to meet all of the fluctuations that come along with the grid just to keep your inverters warm and happy.

As for pushing back on the POCO to change their transformer taps. Good luck with that. Their first priority is to keep the grid stable for all of their customers up and down the power line with any co-generator probably being the last ones they help out.

Even Industrial complexes had to fight low and high voltage swings before and after each weekend when the POCO turned on and off their capacitors to keep the HV within spec. It used to cause all types of heartburn for me in some areas of our plant with lights either going dim and motors tripping out to high voltage spikes and it's after affects. We ended up installing voltage regulating equipment on critical control equipment as well as finding a "sweet spot" voltage tap for our distribution transformers. All the POCO did was say we were just one of their many customers and would work with us the best they could which was not very much.

[bcroe]

There are standards for line voltage; you might want to investigate and then push back harder.

An autotransformer would work, but its a clumsy solution. For openers it needs to be double ended, because if you try to
make an adjustment on just one line, your inverters might still trip out over the imbalance. If say you reduced 250V to 230V,
the shift of 20V represents 8% and the auto transformer size must be rated proportionally, not trivial at this power level. The
auto might have losses on the order of 1 to 5%, depending on quality. So that looks like losing 1/3% of the peak power, but
since it will be on continuously, day, night, rain, etc the overall losses could run well over 1% of generation. Size it too
big, losses go up; too small, it burns up.

A better way out is reprogram the limits of your inverters, a lot easier if running strings. This in fact is not really so different
from the auto transformer; the inverters now put out the same voltage the auto transformer would have. Bruce Roe

[pclausen]

I did discuss it with the PoCo already and they say that it is by design that they set the voltage at the sub-stations to 125V between each leg and ground. So that is why I'm seeing 250ish on average. He said that before my street was upgraded from 7.2kV to 14.4kV, it would have been possible to move me to a different tab on my transformer, but not anymore.

Also spoke to Ubiquiti (microinverter vendor) and they told me I might need to invest in an autotransformer. They said that with an autotransformer, I don't need the full power rating, only the voltage you're trying to change. So in my case, with 6 strings on 20A breakers, that would be 120A and a 10V delta, so a 1.2kW transformer. He said I would loose a couple of % hit.

I see going to autotransformer route as a last resort. Anyone else had to go this route, and if so, any comments to share?