Re: [RE-wrenches] Utility transformer limitations

[Garrison via RE-wrenches]

Hi William, One possible path forward would be to ask the utility co what AC inverter capacity would be allowed. Maybe the solution would be to unplug a micro or two if you are just over the limit. Even better, maybe they would allow you set an export limit on the micros you have installed. I had a recent situation where a 40kW DC system had exceeded a utility transformer by only 2kW AC, so a simple redesign avoided an $8k invoice from the utility. The utility was not transparent about this option at first and only made it clear after some persistence. Good luck, Garrison Riegel Celestar Solar On Dec 25, 2022, at 3:14 PM, Darryl Thayer via RE-wrenches <re-wrenches@lists.re-wrenches.org> wrote:  It is common practice for the utility to overload the transformer a lot for the potential load.  They expect no one will use their service at maximum, furthermore, they expect non coincidence of loads.  Look at the transformer most have a label as to the kW or the unit, and the utility should give you that number along with the impedance.  Note I have had area engineers not understand that solar reduces the load on the transformer.  They have two concerns, you will overload and you will raise the voltage to other customers.  Overload is ridiculous; the transformer must be at least 20 kW if a 15 kW concern is valid.  However, raising the voltage is not.  If all the customers shut off their power, the voltage would rise to the inverter limit,and/or feed current back on the distribution line raising up/downstream customers voltage.  I have had this problem, on three occasions discussions with the utility upper engineering, not local engineer, i prevailed, one case I did not.   In one cast utility allowed connection and put a voltage monitor on secondary voltage, then later allowed permanent connection..   Good luck    On Sun, Dec 25, 2022 at 1:16 PM William Miller via RE-wrenches <re-wrenches@lists.re-wrenches.org> wrote: Wrenched:   Merry Christmas to those of you that observe such traditions, or substitute the winter festivity of your choice.   I helped a previous employee install an Enphase IQ8 system on his home.  He applied for the utility approval concurrently with his building permit  The day he got his final inspection the utility contacted him and claimed "The aggregate generation exceeds the identified transformer rating" and refused him a Permission to Operate letter.   Adding up the service ratings of the homes on his secondary we get about 336 kW of potential consumption.  Adding the grid-tied systems on his secondary we get about 16.5 kW.  How is it that the back-feed exceeds the transformer rating?   I would appreciate any insight on how to consider this situation and how to fight it.   Sincerely,   William Miller   Miller Solar 17395 Oak Road, Atascadero, CA 93422 805-438-5600 www.millersolar.com CA Lic. 773985     _______________________________________________ List sponsored by Redwood Alliance Pay optional member dues here: http://re-wrenches.org List Address: RE-wrenches@lists.re-wrenches.org Change listserver email address & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org There are two list archives for searching. When one doesn't work, try the other: https://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/ http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules & etiquette: http://www.re-wrenches.org/etiquette.htm Check out or update participant bios: http://www.members.re-wrenches.org _______________________________________________ List sponsored by Redwood Alliance Pay optional member dues here: http://re-wrenches.org List Address: RE-wrenches@lists.re-wrenches.org Change listserver email address & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org There are two list archives for searching. When one doesn't work, try the other: https://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/ http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules & etiquette: http://www.re-wrenches.org/etiquette.htm Check out or update participant bios: http://www.members.re-wrenches.org

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