Interconnection at Apartment Complex

[timpollnow]

Hello All,

I am having trouble figuring out a method of PV interconnection for an apartment complex. The inverter output is 168 A and there is 600 A service disconnect followed by a 150 A building meter as well as 24 tenant meters (all branching from the same bus bar). My POCO is Xcel, and they don't typically like dual metered connections so what considerations would I need to figure out to setup a net metered situation?

Thanks in advance,

Newly graduated (and naive) engineer

 

[pv_n00b]

I take it this is a NEM installation. What meters are you trying to credit? Typically these systems back feed the house load meter.

 

[ron]

Do you have a single central inverter or microinveters per panel?

I'm not sure how you could backfeed 167A from a central inverter with the metering you described.

If you have microinveters, then backfeed each house and tenant meter disconnect with the amount of circuits that makeup the ampacity it can handle.

 

[timpollnow]

@ pv_n00B Yes the system will be net metered. The current house meter is 200A and is installed in a bank of 24 tenant meters.

@ron There are (4) 10kw solaredge string inverters being combined to get 168A

 

[jaggedben]

Sounds like you need to kick this back to sales, or otherwise issue an Request For Information back up the food chain.

If they want one system on the 150A meter then they're going to have to decide who pays to upgrade that meter bussing, hopefully it doesn't require replacing the service equipment. If they want more than one system on more than one meter, they need to tell you which meters they want to backfeed and how much each.

(Edit: The house meter is 150A or 200A? You appear to have given two different amp values now. Not that it matters if you have 168A backfeed, that unfortunately requires 210A circuit sizing.)

 

[pv_n00b]

Here are some assumptions made based on you description:

This is a 600A service
The service feeds a multi-meter tenant panel through a 600A disco.
There are 25 meters in the panel, one of which is the house meter.
Each of these meters most likely has a main disconnect breaker and then feeds a distribution panel in each unit.

The house breaker is either 150A or 200A.
The PV output is 168A, which assuming this is a 240/120A service makes it about a 40kWac system.

Only one question remains, are you planning on back feeding just the house meter or all the meters? That seems to me to be a large system just to offset the house loads.

 

[ron]

@ron There are (4) 10kw solaredge string inverters being combined to get 168A

I think you will have trouble with 690.64

 

[GoldDigger]

...
...

Only one question remains, are you planning on back feeding just the house meter or all the meters? That seems to me to be a large system just to offset the house loads.

This is handled by many POCOs through the mechanism of virtual net metering. In this setup the generation, including excess generation, from one meter is used to offset one or more additional meters under the same ownership or administration.
It is not clear to me how this would work when each tenant has an individual account.

 

[ggunn]

I think you will have trouble with 690.64

...which now points to 705.12. Where do you see the trouble?

 

[ron]

...which now points to 705.12. Where do you see the trouble?

I'm not sure how you meet the 120% rule with a 150A meter and 168A of solar PV.

Even if you tried to break it into pieces, where one inverter back-fed the 150A meter, you are out of luck.

 

[ggunn]

I'm not sure how you meet the 120% rule with a 150A meter and 168A of solar PV.

Even if you tried to break it into pieces, where one inverter back-fed the 150A meter, you are out of luck.

I see, but the 120% rule doesn't apply to meters. There may be a problem, though, with 125% of the inverter output being larger than the service. Neither the 150A meter or the 600A disco define the size of the service. If the service is large enough it may just be a matter of getting the meter switched out and landing the inverter output on the busbars of the bus enclosure feeding the tenant meters. 150A seems way small for 24 units.

 

[jaggedben]

I'm not sure how you meet the 120% rule with a 150A meter and 168A of solar PV.
Even if you tried to break it into pieces, where one inverter back-fed the 150A meter, you are out of luck.

Backfeeding a 150A meter with 168A isn't a violation of the 120% rule, but it is a violation of the 705.60 requirements for inverter output circuits.

Interesting question whether the 600A service disconnect ahead of the meters brings the 120% rule into play for the meter bussing. Under the 2011 code that rule applies to 'busbars and conductors' so you would arguably have a problem. Under the 2014 code it applies only to 'panelboards'. I think a meter bank is not a panelboard per se. But then you see those meter banks with the breakers built in next to each meter; are those panelboards? Under either code the 'opposite end' rule only applies to a panelboard. Also under the 2014 code one is allowed to do multiple ampacity and centerfed busbars under engineering supervision.

 

[mgookin]

This is handled by many POCOs through the mechanism of virtual net metering. In this setup the generation, including excess generation, from one meter is used to offset one or more additional meters under the same ownership or administration.
It is not clear to me how this would work when each tenant has an individual account.

The panels belong to the owner, right? Do the tenants deserve credit? Or does the house deserve all the credit?

 

[GoldDigger]

Landing the inverter output upstream of all of the meters is not going to work unless POCO accepts a new revenue grade production meter to feed into their billing software.

 

[timpollnow]

Update: POCO rejected interconnection at the switchgear (in front of all meters). They require a bi-directional meter to replace the building meter for standard net metering. Current plan would be to upgrade meter size and do a load side tap (from the perspective of the utility) on the meter.

Would the 120% rule need to take into consideration all of the tenant breakers?

 

[jaggedben]

The panels belong to the owner, right? Do the tenants deserve credit? Or does the house deserve all the credit?

In most places if you pay a lawyer enough money you can set up ownership however you like.

In California virtual net metering is a state law that allows credits to be apportioned however you agree at the outset, as long as all meters are on the same service. The PV system gets its own meter so essentially no consumption is logged on it, only exports for credit, which are then credited against the participating units' bills. (The new meter does cost the project money, though!).

I have no idea if the OP's project location allows anything similar, it pretty much depends on state law.

 

[jaggedben]

Would the 120% rule need to take into consideration all of the tenant breakers?

No, they are loads. Loads don't figure into the 120% rule.

What code cycle are you on for this project? Interpretation of details could vary a lot between 2011 and 2014, as I alluded to above.

 

[GoldDigger]

There is no 120% rule for service conductors, including bus bars.

 

[jaggedben]

There is no 120% rule for service conductors, including bus bars.

Yes, but if there's a 600A disconnect ahead of those busbars, are they service conductors?

 

[GoldDigger]

Yes, but if there's a 600A disconnect ahead of those busbars, are they service conductors?

You are right about that. The only things that count for 120% rule are the 600A OCPD, the bus rating (not known yet) and the PV amperage. The house and tenant breakers are not relevant.
That assumes that the 600A disconnect really is considered by POCO to be the service disconnect.