Solar interconnect on 600a service

ppsh

Member
Location
CA
Occupation
Electrician
Working on a 7,000 sqft new construction build, solar is an afterthought, solar crew just wants 10/2 Romex stubbed to multiple points on the roof and landed in nearest subpanels.

Service entrance is a 600a 120/240 MSB, runs through an ats then to a distribution panel with a 400a feed to the residence and various distribution to refeed existing utility buildings.

There will be a 400a main breaker panelboard at the residence, feeding a 200a and a 125a subpanel in the house, 200a main breaker subpanel at the detached garage. They are proposing 80a solar backfired at the detached garage, and 80a solar backfeed at the main residence.

Not looking to derate any of the main breakers in this setup, load clac is already pushing 590a for the service.


All the service equipment is purchased and onsite. I'm guessing the 600a distribution panel at the service would also be undersized with 160a of solar backfeed. 120% of 600 is 720, solar backfeed + main would come out to be 760a. Also concerned with the solar interconnections being downstream of the 100kva standby generator.

I'm thinking a supply side tap ahead of the ATS would be the only practical solution. Running into pushback because of having to run additional conduits ~500ft back to the service for it. Still waiting to hear back from the electrical engineer.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Have you explored all of the other possible qualifications as alternatives to the 120% rule?
It is true that a supply side tap gives the greatest flexibility.
If the solar is downstream of ATS you would have to provide a contactor to disconnect PV when the ATS transfers OR a shutdown signal to the PV inverters if possible.
 

pv_n00b

Senior Member
Location
CA, USA
Since they did not design the electrical system to be "solar ready" they get to pay the lack of pre-planning tax, and that tax is 500' of conduct. Your best bet without redesigning the system is a supply-side interconnection ahead of the ATS.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
Working on a 7,000 sqft new construction build, solar is an afterthought, solar crew just wants 10/2 Romex stubbed to multiple points on the roof and landed in nearest subpanels.

Service entrance is a 600a 120/240 MSB, runs through an ats then to a distribution panel with a 400a feed to the residence and various distribution to refeed existing utility buildings.

There will be a 400a main breaker panelboard at the residence, feeding a 200a and a 125a subpanel in the house, 200a main breaker subpanel at the detached garage. They are proposing 80a solar backfired at the detached garage, and 80a solar backfeed at the main residence.

Not looking to derate any of the main breakers in this setup, load clac is already pushing 590a for the service.


All the service equipment is purchased and onsite. I'm guessing the 600a distribution panel at the service would also be undersized with 160a of solar backfeed. 120% of 600 is 720, solar backfeed + main would come out to be 760a. Also concerned with the solar interconnections being downstream of the 100kva standby generator.

I'm thinking a supply side tap ahead of the ATS would be the only practical solution. Running into pushback because of having to run additional conduits ~500ft back to the service for it. Still waiting to hear back from the electrical engineer.
It sounds like you are thinking of microinverters on the roof. One thing you need to check on is if your AHJ will allow Romex to the roof. Many that we deal with require at least MC cable. It also sounds like a multifamily dwelling; something else you will need to know if you are considering a line side interconnection is how it will be metered. If each unit has its own service that may be tricky.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
Working on a 7,000 sqft new construction build, solar is an afterthought, solar crew just wants 10/2 Romex stubbed to multiple points on the roof and landed in nearest subpanels.

Service entrance is a 600a 120/240 MSB, runs through an ats then to a distribution panel with a 400a feed to the residence and various distribution to refeed existing utility buildings.

There will be a 400a main breaker panelboard at the residence, feeding a 200a and a 125a subpanel in the house, 200a main breaker subpanel at the detached garage. They are proposing 80a solar backfired at the detached garage, and 80a solar backfeed at the main residence.

Not looking to derate any of the main breakers in this setup, load clac is already pushing 590a for the service.


All the service equipment is purchased and onsite. I'm guessing the 600a distribution panel at the service would also be undersized with 160a of solar backfeed. 120% of 600 is 720, solar backfeed + main would come out to be 760a. Also concerned with the solar interconnections being downstream of the 100kva standby generator.

I'm thinking a supply side tap ahead of the ATS would be the only practical solution. Running into pushback because of having to run additional conduits ~500ft back to the service for it. Still waiting to hear back from the electrical engineer.

Description is a little unclear, but I'm getting that from the service it goes 600A MCB > ATS > 600A panelboard > various places.

If that 600A panelboard has a 400A breaker for the main residence and 200A or less of breakers feeding other things, then it can meet the 'sum of all breakers rule' and does not have to meet the 120% rule.

That may be the least of your problems though. You need to run conduit from the line side of the ATS either to interconnect the solar there or for contactors, as others have described above.
 
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