3 phase PV

[jaggedben]

Question1
Does this mean that 9 inverters are required??

No. Note the ellipses ("..."), which are intended to convey that the pattern simply repeats for every three additional inverters added to the system. Conceivably there's no limit to the number of inverters in the system.

It's perhaps a little suprising that there are apparently four inverters instead of multiple of 3, but since they are only 3kW inverters, that may fall underneath the utility's threshold for an allowable imbalance between phases. As the Fronious manual reminded me on the very page you referenced, that allowable imbalance is usually 6kW.

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?

No, they would not shut down.

It is possible to imagine how the inverters could be connected in a 'wrong' way, that is outside of the allowable phase to phase imbalance (say, all four inverters connected to one phase). But while that might violate the utility's requirements and perhaps the NEC, the inverters wouldn't know that and they would simply put out their output on each phase. Nor should it affect the net meter, AFAIK.

From what you've told us, which is admittedly still very little, you seem to have a functioning PV system. Maybe you'll get more info that might cast doubt on that, but in the meanwhile I think you might want to eliminate some other basic questions for us:

1) Has the system been approved for operation by the utility and have they installed a net-meter? If not, and if there is a digital meter or smart meter at the site, that meter may simply not be programmed to credit the homeowner for energy exported. That could result in the vast majority of the generated energy not having any effect on the bill. I ask because you say this was recently installed, and usually approvals and meter changing takes several weeks if not months.

2) This is a more ridiculous question, but was the system properly connected to the load side of the meter?

 

[ggunn]

View attachment 7183

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.

To me that image just looks like a bunch of unintelligible dots and it doesn't open to anything better (anything at all, actually).
To answer an earlier question, though, the Fronius IG is a simple grid tied inverter, so it will shut down when the grid is absent and will not power anything under that condition. No batteries.

 

[DelightedInYahweh]

From what you've told us, which is admittedly still very little, you seem to have a functioning PV system. Maybe you'll get more info that might cast doubt on that, but in the meanwhile I think you might want to eliminate some other basic questions for us:

1) Has the system been approved for operation by the utility and have they installed a net-meter? If not, and if there is a digital meter or smart meter at the site, that meter may simply not be programmed to credit the homeowner for energy exported. That could result in the vast majority of the generated energy not having any effect on the bill. I ask because you say this was recently installed, and usually approvals and meter changing takes several weeks if not months.

Please let me clarify just a bit. The system has been up and running for just over a year now. I was not sure at first but that was part of the added information that I received. I will see what I can find out about the utility metering. My only question is, even if there were no effects from 'exported' energy back into the grid, wouldn't the fact that some of the home would draw energy from the PV system make more of a difference than $6-$8 a month on the bill??

2) This is a more ridiculous question, but was the system properly connected to the load side of the meter?

I really don't think that is a ridiculous question at all and is one of the reasons I want to actually look at the system. I have not as of yet been able to go by the house. Either I am out of town busy, or the boss is busy with the business. Still trying though. It is one of the reasons why I am reading as much as I can in regards to the manual and other tid bits just to see how this particular system functions.

Thanks jagged

 

[kwired]

Please let me clarify just a bit. The system has been up and running for just over a year now. I was not sure at first but that was part of the added information that I received. I will see what I can find out about the utility metering. My only question is, even if there were no effects from 'exported' energy back into the grid, wouldn't the fact that some of the home would draw energy from the PV system make more of a difference than $6-$8 a month on the bill??



I really don't think that is a ridiculous question at all and is one of the reasons I want to actually look at the system. I have not as of yet been able to go by the house. Either I am out of town busy, or the boss is busy with the business. Still trying though. It is one of the reasons why I am reading as much as I can in regards to the manual and other tid bits just to see how this particular system functions.

Thanks jagged

If been running for nearly a year - have the differences on electric bills been 6-8 dollars every month?

 

[DelightedInYahweh]

If been running for nearly a year - have the differences on electric bills been 6-8 dollars every month?

The information I am getting is that through the homeowner making comparisons of past bills that that range is the maximum difference that they have seen between them.

If this is a routine difference would that mean that they are seeing the maximum offset their system will give them? Only reason I ask is because that just does not seem a very good return on spending that amount of money for something that will only offset your utility bill by a few bucks???

 

[kwired]

The information I am getting is that through the homeowner making comparisons of past bills that that range is the maximum difference that they have seen between them.

If this is a routine difference would that mean that they are seeing the maximum offset their system will give them? Only reason I ask is because that just does not seem a very good return on spending that amount of money for something that will only offset your utility bill by a few bucks???

I totally agree with you. I don't know if the investment is worth it even at higher offset levels, but if that is the offset level I would have to question if things are set up correctly or if the system even works, which I guess is what you are doing also. 6-8 bucks a month is low enough you can not even say with much confidence that it is exporting any power the owner may just be using less and not even know it, maybe he replaced some appliance with one that is more efficient and that is where the 6-8 bucks has gone.

 

[jaggedben]

You've got a 12kW system, it should be producing something between 10,000 and 20,000 kWh per year, which is to say very roughly between about $80 and $160 worth of electricity a month assuming average US rates somewhere around 10 cents per kWh. (Actual production will obviously be well above that in summer and well below in winter).

even if there were no effects from 'exported' energy back into the grid, wouldn't the fact that some of the home would draw energy from the PV system make more of a difference than $6-$8 a month on the bill??

Not necessarily. On average one would probably expect a slightly bigger difference, that's true. But it's pretty hard to say without knowing anything whatsoever about the customer's usage and habits. It is not entirely implausible that the lack of crediting exports would result in reducing savings to between 5 or 10 percent of what they should be. If you think about it, a PV system is typically only producing at a substantial fraction of it's peak power for about 5-6 hours of the day. So if usage is constant, that's only about 25% that gets offset, and if usage skews towards the evenings and night time, it could be well less than that.

If the customer is on a time-of-use rate that would make a difference. But in any case, from what you've told us so far, a misprogrammed utility meter (or a clerical error in crediting exports) has not been ruled out.

 

[DelightedInYahweh]

You've got a 12kW system, it should be producing something between 10,000 and 20,000 kWh per year, which is to say very roughly between about $80 and $160 worth of electricity a month assuming average US rates somewhere around 10 cents per kWh. (Actual production will obviously be well above that in summer and well below in winter).



Not necessarily. On average one would probably expect a slightly bigger difference, that's true. But it's pretty hard to say without knowing anything whatsoever about the customer's usage and habits. It is not entirely implausible that the lack of crediting exports would result in reducing savings to between 5 or 10 percent of what they should be. If you think about it, a PV system is typically only producing at a substantial fraction of it's peak power for about 5-6 hours of the day. So if usage is constant, that's only about 25% that gets offset, and if usage skews towards the evenings and night time, it could be well less than that.

If the customer is on a time-of-use rate that would make a difference. But in any case, from what you've told us so far, a misprogrammed utility meter (or a clerical error in crediting exports) has not been ruled out.

Very interesting. So my next step( as you have already directed me jagged) is to find out some information in regards to the utility meter. I will see what I can do.

Man I must say I am VERY VERY grateful for the time and experience that ALL of you have been so willing to share. It just gets me more and more excited about being an electrician seeing how vast a repository of detailed information each of you have and are willing to share!!! Thanks everyone ever so much.

 

[ggunn]

Very interesting. So my next step( as you have already directed me jagged) is to find out some information in regards to the utility meter. I will see what I can do.

Man I must say I am VERY VERY grateful for the time and experience that ALL of you have been so willing to share. It just gets me more and more excited about being an electrician seeing how vast a repository of detailed information each of you have and are willing to share!!! Thanks everyone ever so much.

On the installations we do, there is always a utility grade meter on the output from the PV inverter(s) that logs what a system is producing. Beyond that, larger systems typically also incorporate some sort of real time monitoring. Simply comparing utility bills won't give you a good read on system output; you cannot separate usage from production by reading only the utility meter. It would seem foolhardy to me to spend $80k on a system and not have a way of knowing precisely what it is producing.

Is the installer still in business? They would know exactly what was installed and what it should be producing, unless they are of the fly-by-night ilk who look for a patsy that they can take advantage of and charge them a lot of money for a slipshod installation. I hope that that's not what you are dealing with. Unfortunately, those guys still exist and give the rest of us in the industry a black eye with every system they sell. The good news is that as the industry matures and becomes more transparent these charlatans are finding it harder and harder to rip people off.

If you ever get on site, look for a meter on the PV system output. Failing that, on a sunny day you might could turn off all the breakers in the main service and any subpanels except for the backfeed from the inverters, and look at what the utility meter is doing.

 

[DelightedInYahweh]

Update

Update

I got the information that the utility required to tell me what type of service the homeowner was utilizing and the home is being net metered . Seems this may be what ggunn described as a charlatan indeed! One of the other guys is going to look in to whether or not the guy is still around and see if we can touch base with him, but seeing how the system is now over a year in service I am sure he will not be much interested.

Not real sure why it has even gone this long without things being figured out, but it sure makes me want to learn even more in regards to the field of photovoltaics. And the story continues...........

 

[jaggedben]

Not sure I understand your update. (Did you mean to say that the home isn't being net-metered?)

 

[DelightedInYahweh]

No the utility company stated that it is being net metered. So evidently there must be something going on with the system. The confusing part for me is that the inverters show power being produced and an ammeter shows that it is flowing along the conductors to the panels. HMMM

 

[fmtjfw]

Have you verified that the inverter outputs are connected phase-to-phase and not phase-to-neutral?

What are the current readings from the inverter outputs in bright sun?
What are the voltages across the inverter outputs?
Do the panels get lots of sunshine or are they partly shadowed?
If I had a $80K system with such a poor payback I'd put a production KWH meter in the feed from the inverters to the connection to the incoming service. Or you could put a recording meter around each phase lead from the inverters for awhile.

 

[DelightedInYahweh]

FMTJFW,

The boss has spoken along the same lines as you in regards to monitoring the three phases for a period of time and seeing what that comes up. This evidently is not a project that he is putting a lot of effort into, so not real sure when or even if this will occur.

As for placement, there is a flat roofed garage on the south side of the home. The panels are installed here with a slight degree of angulation and remain constantly in the sun throughout the day. No trees, no buildings, nothing to impede the direct radiation from striking them.

As to the verification of connections and output in full sunshine all the information I have been giving to you all has come from one of the senior electricians in the company. He is not very familiar with PV, so he is limited in what he is comfortable doing and not doing. I have not even put my eyes on the set up. Only saw the inverters for a very short time and it was very cloudy the day I went over, but they were still reading power output.

I was just mining information to see if anyone had maybe dealt with this type of issue and if I could get any leads as to what might be the root cause. Sorry guys for the lack of information. I just feel disgusted that the homeowner put out so much money and is getting such poor results. Just trying to help.

 

[ggunn]

I got the information that the utility required to tell me what type of service the homeowner was utilizing and the home is being net metered . Seems this may be what ggunn described as a charlatan indeed! One of the other guys is going to look in to whether or not the guy is still around and see if we can touch base with him, but seeing how the system is now over a year in service I am sure he will not be much interested.

Not real sure why it has even gone this long without things being figured out, but it sure makes me want to learn even more in regards to the field of photovoltaics. And the story continues...........

I just noticed that you are located in Lake Charles. That's my home town!

Hope you get all this straightened out.

 

[ggunn]

Have you verified that the inverter outputs are connected phase-to-phase and not phase-to-neutral?

What difference would that make? There are ways, depending on the inverters and the service voltage, to connect either way.

 

[DelightedInYahweh]

I just noticed that you are located in Lake Charles. That's my home town!

Hope you get all this straightened out.

Another Lake Charles Sparky on Holt's Forum heh heh heh...........Glad to have met you ggunn!

 

[ggunn]

Another Lake Charles Sparky on Holt's Forum heh heh heh...........Glad to have met you ggunn!

Actually, I am an engineer, but don't tell anyone, OK?

 

[DelightedInYahweh]

Actually, I am an engineer, but don't tell anyone, OK?

OHHHH DEAR!!! One of THOSE guys!!!!!!!!:slaphead:

 

[DelightedInYahweh]

Just kidding!