3 phase PV

[DelightedInYahweh]

A homeowner recently called our company with questions about a 3 phase pv system that had been recently installed into their current electrical system. it is a residential home and I am sure it is not 3 phase utility power. From the PV side it seems that the system is putting out adequate power, but the homeowner has only seen an $8 difference in their utility bill.

I was just wondering if anyone out there had any pointers of where or what to be looking for. Our company does not do much if any PV work, so we are taking it slow and going through everything. The boss has started monitoring the phases to see if anything can be seen through that avenue. But I just wanted to see if any of you might have run in to this issue before and what we might be able to look at specifically.

Thanks in advance. Please let me know if you need any specific information and I will do my best to get what I can.

 

[jaggedben]

I think we need way more information.

Generally it would take a very - (how shall we put it) - dense person to hook up a 3 phase inverter to a single phase supply. It is doubtful that this would result in even an $8 difference in the bill because a 3 phase inverter would not turn on if it didn't find a stable 3 phase supply. One exception might be an Enphase system that improperly used 3-phase cabling. In that case one third of the inverters would turn on (and 8$ would be a pretty small system, like six panels).

 

[DelightedInYahweh]

I think we need way more information.

Generally it would take a very - (how shall we put it) - dense person to hook up a 3 phase inverter to a single phase supply.

Well, I can in no way disprove your comment on the 'denseness' of the individual who installed this system. I really don't know who in these parts even installs PV systems. There's not a HUGE market here at this time. I just got bits and pieces from the boss. I just wanted to see if I could glean anything from you guys that might assist us in rectifying the issue seeing this homeowner paid over $30,000 for this project.

It is possible I may need to get clarification from the boss. Please let me know of any specific information you may need and I will see if I can acquire it.

Thanks jagged!!

 

[iwire]

You really need to find out the exact make and model of inverter.

As Jag pointed put very few 3 phase inverters would ever go on line at all without a 3 phase supply. It would see the missing phase as a utility outage and stay offline.

 

[DelightedInYahweh]

Thanks iwire.

I will get more information and make sure what type of service is coming from the utility.

 

[kwired]

Even if it does connect...

If you connecte a three phase supply to a single phase load you only get about 58% of the three phase capacity and the third phase does nothing.

If electric bill is only $8 lower they may have simply used less energy that month, and not necessarily put anything back into grid, or shaved any demand from grid.

 

[iwire]

Even if it does connect...

Truth be know when I said 'few' I actually cannot think of any 3 phase listed inverter that would go into 'grid interactive' mode with a phase missing.

That would be a listing violation [UL 1741] as far as I know. (The anti-islanding / no back feed requirements)

 

[kwired]

Truth be know when I said 'few' I actually cannot think of any 3 phase listed inverter that would go into 'grid interactive' mode with a phase missing.

That would be a listing violation [UL 1741] as far as I know. (The anti-islanding / no back feed requirements)

I know little about PV installations - most of what I am aware of I have learned reading here.

That said my reply indicated if you were to connect "any three phase supply" to a single phase distribution system you would only be able to use about 58% of the total capacity of the supply.

 

[iwire]

I know little about PV installations - most of what I am aware of I have learned reading here.

Understood, that was why I provided the UL standard in case you wanted to check it out.

That said my reply indicated if you were to connect "any three phase supply" to a single phase distribution system you would only be able to use about 58% of the total capacity of the supply.

Understood again.

 

[kwired]

Understood, that was why I provided the UL standard in case you wanted to check it out.





Understood again.

Happy to see we both understand

 

[DelightedInYahweh]

Sorry guys, the boss did not have the specific information right off hand. I will do my best to get it before the end of the week.

 

[ggunn]

A homeowner recently called our company with questions about a 3 phase pv system that had been recently installed into their current electrical system. it is a residential home and I am sure it is not 3 phase utility power. From the PV side it seems that the system is putting out adequate power, but the homeowner has only seen an $8 difference in their utility bill.

I was just wondering if anyone out there had any pointers of where or what to be looking for. Our company does not do much if any PV work, so we are taking it slow and going through everything. The boss has started monitoring the phases to see if anything can be seen through that avenue. But I just wanted to see if any of you might have run in to this issue before and what we might be able to look at specifically.

Thanks in advance. Please let me know if you need any specific information and I will do my best to get what I can.

Coming in late, but...

It was the homeowner who told you that the PV system was 3 phase? Does he know what he is talking about? In addition to what others have said about it being doubtful that a 3 phase system would even turn on when connected to a split phase service, three phase inverters suitable for residential applications are rare. I'm just speculating, but many residential PV systems have three DC strings; perhaps the homeowner is confused about what he has? Knowledge of the inverter make and model will clear that up pretty quickly.

As to the $8/month difference on his bill, how is he quantifying that? Is he using several years worth of bills from before and after his system was installed, or is he just comparing a couple of monthly bills? A small sample size will not yield results that really mean anything. Lastly, the $8/month may be all he can expect from his system, depending on its size and how well it was installed.

It's probably not a 3 phase inverter, though.

 

[DelightedInYahweh]

Ok, here is what I have up to this point.

3phase 208Y/120 supplying the home do not know when or who installed the system, but I think that the boss' company did before I came to work for them. The home is about 9500 sq ft. Quite old, do not know the exact age, but am very sure wiring is NOT up to current code. The PV system is 3 phase, but I do not as of yet have a make and model of the inverter.

I do know that the installer did all of his work outside of the home. I can not be very specific about what data the homeowner is utilizing to come up with his $8 a month total. Sorry guys I am trying to squeeze bits and pieces out of the boss as and when I can. I tried to go by the home today and take a look at everything myself but that fell through.

In brainstorming I thought about whether there could be a bonding/grounding situation since the house is so old. If maybe the feed is not simply going to ground rather than to service the home. Was wondering if shutting down the utility service on the home and test to see if anything powered up(not sure if this was done yet, just spitting off things that have been flying around in my head.)

I hope maybe this will give some direction, but I will continue to press for details and am doing my best to put my physical eyes on the system in order to get as much detail as possible.

Thanks everyone, I appreciate the wisdom of three phase PV not supplying single phase. It helped me to ask the right questions to get more answers.

 

[ggunn]

Ok, here is what I have up to this point.

3phase 208Y/120 supplying the home do not know when or who installed the system, but I think that the boss' company did before I came to work for them. The home is about 9500 sq ft. Quite old, do not know the exact age, but am very sure wiring is NOT up to current code. The PV system is 3 phase, but I do not as of yet have a make and model of the inverter.

I do know that the installer did all of his work outside of the home. I can not be very specific about what data the homeowner is utilizing to come up with his $8 a month total. Sorry guys I am trying to squeeze bits and pieces out of the boss as and when I can. I tried to go by the home today and take a look at everything myself but that fell through.

In brainstorming I thought about whether there could be a bonding/grounding situation since the house is so old. If maybe the feed is not simply going to ground rather than to service the home. Was wondering if shutting down the utility service on the home and test to see if anything powered up(not sure if this was done yet, just spitting off things that have been flying around in my head.)

I hope maybe this will give some direction, but I will continue to press for details and am doing my best to put my physical eyes on the system in order to get as much detail as possible.

Thanks everyone, I appreciate the wisdom of three phase PV not supplying single phase. It helped me to ask the right questions to get more answers.

A couple of things...

Unless the system is a hybrid system with a battery bank, if you shut down the utility service the PV system will not operate. Those systems are relatively rare and I don't know of any that are three phase.

I'm still very curious about this inverter. Single three phase inverters small enough for residential systems do exist, but they are not very common. The service is 208/120 with a high leg, right? I believe that the preferred way to connect to that service would probably be 240V split phase on the two legs with the center tap.

When an inverter is running but producing far less power than it should, the problem is almost always on the DC side. Squirrels chewing wiring is a common cause of this; another is severe soiling of the solar modules. Shading from trees that have grown since the system was installed can cause problems, and even a little shading can cause major losses, depending on what part of the array is being shaded. It is unlikely that power is flowing out of the inverter to ground; if an output conductor were shorted to ground, the inverter would not be able to synch with the utility service and would shut down completely. Likewise, if current were flowing to ground on the DC side, it would trip the ground fault circuitry in the inverter and shut it down.

If the homeowner says he is only seeing $8 difference in his utility bill, then it's possible that the PV system could be off line. The utility bill for a 9500 sf house, especially an older one, is going to be so large that $8/mo is down in the noise.

Good luck!

 

[DelightedInYahweh]

A couple of things...

Unless the system is a hybrid system with a battery bank, if you shut down the utility service the PV system will not operate. Those systems are relatively rare and I don't know of any that are three phase.

I do realize that under most typical installations the system shuts down when there is no utility service, but I have also read that there are systems designed to be back up capable if and when the utility service shuts down. That is why I began thinking about the possibility of opening the utility main and seeing what took place and if there would be any viable information from that process.

I'm still very curious about this inverter. Single three phase inverters small enough for residential systems do exist, but they are not very common. The service is 208/120 with a high leg, right? I believe that the preferred way to connect to that service would probably be 240V split phase on the two legs with the center tap.

As am I ggunn. I have still come up empty on being able to put my eyes on this system. The boss has me tied up on jobs so I can not get to it during the day. I may just have to put this to rest and leave it up to him to work his way through it. I am just trying to be helpful and assist the homeowner in their dilemma.

When an inverter is running but producing far less power than it should, the problem is almost always on the DC side. Squirrels chewing wiring is a common cause of this; another is severe soiling of the solar modules. Shading from trees that have grown since the system was installed can cause problems, and even a little shading can cause major losses, depending on what part of the array is being shaded. It is unlikely that power is flowing out of the inverter to ground; if an output conductor were shorted to ground, the inverter would not be able to synch with the utility service and would shut down completely. Likewise, if current were flowing to ground on the DC side, it would trip the ground fault circuitry in the inverter and shut it down.

If the homeowner says he is only seeing $8 difference in his utility bill, then it's possible that the PV system could be off line. The utility bill for a 9500 sf house, especially an older one, is going to be so large that $8/mo is down in the noise.

Good luck!

Thank you so much ggunn for your input. At least I have some direction for if and when the boss allows me to get my dirty little hands in this project hehhehheh. The system is just newly installed so I highly doubt that squirrels, dirt, or trees are the issue. The system has not been online for more than a few months from what I understand.

I am very grateful for yours and everyone else's input. I guess I was just looking for a smoking gun, or an ah ha that's it kinda solution!! But I see I just do not have and do not seem to be able to get enough information to help anyone out. Thanks everyone.

 

[ggunn]

I do realize that under most typical installations the system shuts down when there is no utility service, but I have also read that there are systems designed to be back up capable if and when the utility service shuts down. That is why I began thinking about the possibility of opening the utility main and seeing what took place and if there would be any viable information from that process.

It's true that some (a very small percentage) PV systems are equipped to keep running in a backup mode when the grid goes down, but those systems are 1) a whole lot more expensive than a "normal" grid tied system, 2) isolated from the grid so when you open the main disconnect both the line and load sides of the switch will be de-energized, and 3) connected to a large battery bank. It is possible to have a battery backup three phase PV system, but the only way I know to do it would require at least 4 inverters (3 Sunny Islands and at least one Sunny Boy).

You can tell a lot from just looking at the inverter; if there isn't a very large and obvious battery bank very close to it connected with short fat conductors, it's not a backup system.

 

[DelightedInYahweh]

Thanks ggunn,

I got to talk with one of the more senior electricians in our company. He said he has already looked at it and everything 'looks' electrically sound from the house end, but he said quite clearly he was not real familiar with the PV side of it. He told me he was going by the house at some point this week and he would see what kind of information he could get me. So maybe he will have something.

Guess we'll see!

 

[DelightedInYahweh]

Ok, I finally got some information from the electrician I spoke of. If the image does not come out better when I submit this I will post a better one. But here is the information. If you click on the image above the image that pops up is much better than the one below.

The system is about a year old. The homeowner paid a bit over $80,000 for the system. The homeowner asked the company to come take a look at it when it was first installed due to the fact that the issue I described in previous posts was taking place. The boss sent an electrician to inspect, but he had very limited understanding of PV systems. From the AC side he could see nothing amiss. He did tell me that when he put his amp meter on the AC side of the inverters he did get readings from all 4.

On the image I submitted you can see the wattage output for yesterday. Now we have been having storms for about a week so there was heavy cloud cover and the readout on the inverter display was taken down at about 3pm yesterday.

The inverters are Fronius IG Plus
Model # 3.0_1UNI
PART 4210101800
Serial # 20471769
208/240/277
14.4AMPS 3000Watts

The utility service is 208Y/120 coming into the house. If I think of anything else the electrician told me I will post. If you all need more information please let me know and I will dig a bit more.
Thanks a TON for everything so far.

 

[DelightedInYahweh]

Ok, page 36 of the Fronius manual states this:

"208 V / 240 V:- Connect Fronius IG Plus No. 1, No. 4, No. 7, ... to L1 and L2
- Connect Fronius IG Plus No. 2, No. 5, No. 8, ... to L2 and L3
- Connect Fronius IG Plus No. 3, No. 6, No. 9, ... to L1 and L3"


Question1
Does this mean that 9 inverters are required??

Question2
IF the system was not connected in this manner would the inverters potentially still show that they are outputting power to the system or would the inverter simply shut down?

 

[jaggedben]

On the image I submitted you can see the wattage output for yesterday. Now we have been having storms for about a week so there was heavy cloud cover and the readout on the inverter display was taken down at about 3pm yesterday.

The inverters are Fronius IG Plus
Model # 3.0_1UNI
PART 4210101800
Serial # 20471769
208/240/277
14.4AMPS 3000Watts

It's a bit of a guessing game without a simultaneous irradiance reading, but if there was medium cloud cover and the inverters were each outputting about 30% of their max output, that seems generally plausible and does not give any indication of a problem.