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Thread: 26kW residential system?

  1. #1
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    26kW residential system?

    Any ideas on how to add, without a service upgrade, 20kW (two 10kW inverters) to an existing 6kW system on a residential property serviced with a main panel (200A), a sub panel (100A) and a sub sub panel?

    The existing PV system (6kW) was installed with a 30A breaker located immediately adjacent to the center-fed 200A main breaker. It's been in place for 10 years.

    The local utility (SDG&E), does not permit line-side taps, but does offer a Renewable Meter Adapter (RMA) which features a 60A breaker.

    Options?

    The owner of the property has already purchased all of the equipment (60 panels and 2 10kW inverters) and is now looking for a contractor for installation.

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    Quote Originally Posted by mcsolar View Post
    Any ideas on how to add, without a service upgrade, 20kW (two 10kW inverters) to an existing 6kW system on a residential property serviced with a main panel (200A), a sub panel (100A) and a sub sub panel?

    The existing PV system (6kW) was installed with a 30A breaker located immediately adjacent to the center-fed 200A main breaker. It's been in place for 10 years.

    The local utility (SDG&E), does not permit line-side taps, but does offer a Renewable Meter Adapter (RMA) which features a 60A breaker.

    Options?

    The owner of the property has already purchased all of the equipment (60 panels and 2 10kW inverters) and is now looking for a contractor for installation.
    Is that normal to not allow a line side tap? I might try to figure out the reasoning behind that and clarify that's how it really is.

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    Quote Originally Posted by Supratachophobia View Post
    Is that normal to not allow a line side tap? I might try to figure out the reasoning behind that and clarify that's how it really is.
    I wouldn't say it is normal, but I have heard of this silly requirement by some utilities. One option is to use 230.40 exception #2, which really is just what a supply side connection is anyway, and qualify the busbar on the panelboard serving the pv with the "sum of all over current devices" provision.
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

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    Quote Originally Posted by Supratachophobia View Post
    Is that normal to not allow a line side tap? I might try to figure out the reasoning behind that and clarify that's how it really is.
    We deal with an AHJ that does not allow line side PV interconnections, as well as a couple who allow nothing but them. That's just one of the differences; we keep an evolving document on the different rules in different jurisdictions in Texas. It's up to five pages now, I believe.

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    Quote Originally Posted by mcsolar View Post
    Any ideas on how to add, without a service upgrade , 20kW (two 10kW inverters) to an existing 6kW system
    Quote Originally Posted by electrofelon View Post
    One option is to use 230.40 exception #2 , which really is just what a supply side connection is anyway, and qualify the busbar on the panelboard serving the pv with the "sum of all over current devices" provision.
    Just wanted to add a little more to this. Note you could do this without a service upgrade. 230.90(A) exception #3 allows the sum of the OCPD's service as the service disconnect to exceed the ampacity of the service conductors, so you could leave the meter and everything upstream as is. Tap the conductors on the load side of the meter into two sets, add a new panelboard to the new set and make a load side connection in it.
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

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    mcsolar

    No, you can't do this without changing the service equipment. (You don't need to upgrade the service, just the service equipment.) Electrofelon has the right idea, just create a second service disconnect. Put in a meter socket, gutter, replace the existing with a 200A panel (not meter/main) and put in a separate 125bA for the solar.

    I'm skeptical that SDG&E can really disallow supply side connections in general, but if you've got a meter/main combo it makes no difference. You have to replace that.

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    Quote Originally Posted by jaggedben View Post
    I'm skeptical that SDG&E can really disallow supply side connections in general...
    But an AHJ can, and they do. As we have discussed many times, an AHJ can amend the NEC in any way they see fit within their area of jurisdiction. They can add restrictions that aren't in the code and they can choose not to enforce some that are.

    We operate throughout the state of Texas, and in doing so we have encountered two AHJs that completely prohibit line side connected PV as well as a couple that require all PV to be line side connected. One of them has added a restriction that virtually disallows any PV interconnection in a subpanel, even though the way it is (poorly) written into their Interconnection Guide belies a misunderstanding of basic electrical theory. We challenged it and lost the fight.

    It would be great if all AHJ's looked at PV the same way, but that ain't gonna happen.

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    IOUs in California are not AHJs. And AHJs in California can't make their own rules without going through a specific process with the state. So we don't get as much variation out here on this stuff.

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    Quote Originally Posted by jaggedben View Post
    IOUs in California are not AHJs. And AHJs in California can't make their own rules without going through a specific process with the state. So we don't get as much variation out here on this stuff.
    Lucky you.

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    What am I missing--how is a second service disconnect that only serves PV any different from a line-side tap? Or is the idea to put a little load on the second service disconnect, too?

    Another option is that if a 200A service disconnect can be added in front of the existing 200A main panel, then the 200A feeder from the new service disconnect to the main panel can be tapped per 705.12(D)(2)(1).

    Cheers, Wayne

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