I made a big mistake and didn’t realize it soon enough

[BackCountry]

Well, I have to admit when I’m wrong: and I made an error that I should have caught, and now I’ve got a potential $21,000 loss if I can’t figure out some way to mitigate it.

Background: 23kw (three SMA7.7’s) single phase 240v PV system that we built that’s in the PTO process with PG&E, it’s NEMA with one generating meter and 4 load meters. All of the load meters are at least 3-500’ away.

I never thought to pre apply or check the transformer on the generating meter, it’s an ag property and the pole is around the corner, it has an existing 200A service — I never looked up. I should have, it’s a 10kva transformer.

PG&E is stipulating either $21,000 to upgrade the transformer, or…? I’ve never tried to export limit before, has anyone done this with SMA inverters, if so — do you need the data manager to do it? And finally, any experience with PTO using export limiting?

If I did export limit, it would likely not be a huge difference — this system maxes at 19kw during testing, and PG&E would limit me to 13kw.

The other option is to re permit, and trench 500’ to another meter with a 25kva transformer, pull 4/0 to that and re submit.

I’m all ears, and I’ll be looking up more often. I for some reason mistakenly thought that PG&E was on the hook for lower than 30kw, and I was wrong.

 

[petersonra]

What does the customer have to say about it? Are they willing to pay for a 23 kilowatt system that only generates 13 kilowatts?

Maybe you should just get rid of one of the three systems

 

[BackCountry]

I haven’t worked through the options with them yet, I wanted to make sure what I’m thinking about doing is going to work first.

Their active load on the generating meter is likely enough to bring them down below the max export of 13kw on most days anyway. During testing in the summer, the max output was 19kw.

The biggest question is: has anyone used SMA’s active power limiting functions successfully with their utility?

 

[Hv&Lv]

Well, I have to admit when I’m wrong: and I made an error that I should have caught, and now I’ve got a potential $21,000 loss if I can’t figure out some way to mitigate it.

Background: 23kw (three SMA7.7’s) single phase 240v PV system that we built that’s in the PTO process with PG&E, it’s NEMA with one generating meter and 4 load meters. All of the load meters are at least 3-500’ away.

I never thought to pre apply or check the transformer on the generating meter, it’s an ag property and the pole is around the corner, it has an existing 200A service — I never looked up. I should have, it’s a 10kva transformer.

PG&E is stipulating either $21,000 to upgrade the transformer, or…? I’ve never tried to export limit before, has anyone done this with SMA inverters, if so — do you need the data manager to do it? And finally, any experience with PTO using export limiting?

If I did export limit, it would likely not be a huge difference — this system maxes at 19kw during testing, and PG&E would limit me to 13kw.

The other option is to re permit, and trench 500’ to another meter with a 25kva transformer, pull 4/0 to that and re submit.

I’m all ears, and I’ll be looking up more often. I for some reason mistakenly thought that PG&E was on the hook for lower than 30kw, and I was wrong.

$21,000??
Thats ridiculous. Those XFs cost us about $1500 each for a 25kVa.
Takes two guys 30 minutes to change out.

 

[ggunn]

This kind of thing is my worst professional nightmare.

Take a look at 705.10(A) and 705.13.

 

[BackCountry]

This kind of thing is my worst professional nightmare.

Take a look at 705.10(A) and 705.13.

It’s my living nightmare currently!

I made a test application on PG&E’s interconnection portal, and it did give me the option to use a PCS with SMA inverters (it showed them as listed and certified). I think that’s my best bet.

The only other slight glimmer of hope: I remember seeing a PG&E and California PUC memo that put the burden of transformer upgrades for EV chargers on the utility. If that’s still valid, I could apply to add an EV charger(s). Slim chance.

I agree, $21,000 is absolutely ridiculous. I also think that a 10kva transformer serving a large property is likely the result of a service upgrade where they never chose to upgrade the transformer, likely because the load calc never changed.

 

[GeorgeB]

I certainly don't know PG&E policies, but can you PERHAPS get low enough rating by pointing one array W or NW, one E or NE, and one as you probably planned for all, S? This would lower overall slightly, reduce maximum, and distribute generation over a longer part of the day.

 

[jaggedben]

I would have made the same mistake because I thought that under 30kw you would not be responsible for that. But maybe it's because no other customer's share that transformer, or because it's ag.

Did PG&E actually say that they'd accept PCS export limiting? Sorry I can't help with the details.

 

[jaggedben]

I certainly don't know PG&E policies, but can you PERHAPS get low enough rating by pointing one array W or NW, one E or NE, and one as you probably planned for all, S? This would lower overall slightly, reduce maximum, and distribute generation over a longer part of the day.

PG&E won't care about any of that, although it would make the project more economical with export limiting. But I'm pretty sure he's already built it.

 

[synchro]

$21,000??
Thats ridiculous. Those XFs cost us about $1500 each for a 25kVa.
Takes two guys 30 minutes to change out.

I agree that price is a total ripoff if it's just for a transformer. I wonder if they are thinking that the MV conductor runs also need to be replaced? But I doubt that would be necessary because, for example, 25kVA would only be 6A at 4160V.

 

[BackCountry]

I would have made the same mistake because I thought that under 30kw you would not be responsible for that. But maybe it's because no other customer's share that transformer, or because it's ag.

Did PG&E actually say that they'd accept PCS export limiting? Sorry I can't help with the details.

It’s because it’s a single customer off that transformer. I never knew this little loophole existed either, I guess in the past we’ve always had a 25kva and never knew the wiser. Many of these ag installs are single customer on a transformer just because of the size of the parcel.

They didn’t say they’d accept it yet; however, I do see in YourProjects the option to select export limit. I’ve never tried it before, was hoping someone has.

 

[BackCountry]

I agree that price is a total ripoff if it's just for a transformer. I wonder if they are thinking that the MV conductor runs also need to be replaced? But I doubt that would be necessary because, for example, 25kVA would only be 6A at 4160V.

The price is insane, and no they just need to swap the pot out and that’s it. They do this insane cost calculation.

 

[ggunn]

I certainly don't know PG&E policies, but can you PERHAPS get low enough rating by pointing one array W or NW, one E or NE, and one as you probably planned for all, S? This would lower overall slightly, reduce maximum, and distribute generation over a longer part of the day.

PV system conductor and OCPD sizing are based on maximum published output current from the inverter(s) irrespective of DC loading.

 

[LarryFine]

It could be someone pulled the price from a book, and is actually for a new install and not an up-size.

 

[synchro]

I wonder if the price for a transformer upgrade would've been significantly less if it was not for a PV installation, but just because some more loads were added.

 

[ggunn]

It’s my living nightmare currently!

I feel your pain. We ran into a similar situation a few years ago where we installed PV systems on two car dealerships that were on adjoining properties. We sized the systems to fit the sizes of the building services, not realizing that they were fed from the same utility transformer. The total of the AC ratings of the two systems exceeded the kVA of the transformer, and we didn't find out until both systems were installed. We had to pay for the upgrade ourselves, since after the systems were installed with the customers impatiently waiting for us to turn them on we had no bargaining leverage.

It was a lot of tuition to pay for that bit of education.

 

[petersonra]

The price is insane, and no they just need to swap the pot out and that’s it. They do this insane cost calculation.

ComEd here does something similar. It is based on their estimate of the total cost of the installation over its lifetime converted to current dollars. It is a reasonable way to charge for such things IMO. Why should other ratepayers now and in the future pay for equipment that is dedicated to you?

 

[pv_n00b]

Had that happen to me with PG&E before, maybe 8 or 9 years ago. The numbers are a little hazy but it was something like we had a 1,200A service SWBD and did not find out until the interconnection application phase that PG&E had only given them a 300kVA pad mounted service transformer. This was a municipal design bid build project so the interconnection phase did not happen until the contractor started the build process. The PV system I was working with was something like 350kW AC. Upsizing the transformer to what was normally the next size up at 500kVA was not possible because PG&E said they were discontinuing that size so they could only provide a 750kVA and since that was way over the load they would charge a fee every month for the oversized transformer. We were using SolarEdge inverters but PG&E would not accept the export limiting system that was built in, we had to either install an expensive non-export relay or have the factory limit the output of the inverters. We went with the factory limit option. Good luck.

 

[Zee]

Their active load on the generating meter is likely enough to bring them down below the max export of 13kw on most days anyway. During testing in the summer, the max output was 19kw.

The biggest question is: has anyone used SMA’s active power limiting functions successfully with their utility?

I have never limited export. Don't now how.
However, how would SMA know what the net export is? Seems like SMA would just measure gross solar output at the inverter, not net export at the meter??

Also, I second splitting arrays across orientations - if cost effective. Especially E-W if relatively steep pitch. However, if shallow pitch, won't make much diff.
Of course depends on specifics of array and roof.

 

[ggunn]

Also, I second splitting arrays across orientations - if cost effective. Especially E-W if relatively steep pitch. However, if shallow pitch, won't make much diff.
Of course depends on specifics of array and roof.

PV AC system size is generally determined by the maximum inverter output capability irrespective of how the inverters are loaded on the DC side.