Best Practice for Solar Inverter Connection Point in Relation to ATS

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  • doraimom
    Junior Member
    • May 2024
    • 3
    #1

    Best Practice for Solar Inverter Connection Point in Relation to ATS

    Hi.
    I recently moved to Australia and I'm currently working in a project that will have a solar power system added.
    I have previous experience with residencial solar systems, but under different standards.

    The current project is the design and construction of a Sewage Treatment plant.
    We subcontracted a company to be the electrical designer.
    When the client asked for a solar system, the electrical designer added it downstream of the ATS.
    I immediately mentioned that I didn't agree with that due to multiple reasons:
    • The inverter placed downstream of the ATS would require physical interlocks and add complexity.
    • The inverter placed downstream of the ATS could beckfeed the generator.
    • The inverter placed downstream of the ATS would add extra costs (extra hardware for interlock).
    • The inverter placed downstream of the ATS would waste the energy from the panels everytime the ATS switches from mains to generator due to some trip condition (brown-out, etc.). Since we had in the Function Description Specification document written that when the ATS switches to the generator due to a trip cause, the mains would be monitored for four hours, before switching back to mains. So, the waste here could be significant. Currently, I was able to reduce that suggested time to 1 hours.
    The electrical designer, on the other hand, said that the logical position, in his mind, for the solar system to connect to the grid would be downstream of the ATS. He invited a solar specialist to address those concerns, but during the meeting he kind of said both lines of thought were ok and he could see reasons for each position defended there. That being said, the electrical designer sticked to his original design placing the inverter downstream of the ATS. I still disagrees with that.

    The solar specialist also said that most inverters can detect when power is being supplied by a generator, so they will automatically disconnect. (I would still add interlocks and I wouldn't trust in the inverter completely for safety).

    I tried to find any electrical standard or relevant document that would advice the best practice for the inverter's connection point, but I couldn't find anything specific yet.
    That's mainly what I'm seeking here. The opinion of the comunity is relevant, but a documented reference is even more relevant. Can anyone help me here with some guidance?

    I even tried chatGPT, but even though he advices to connect inverters upstream of ATS, it doesn't give any specific reference for suggesting that.
    From ChatGPT:
    "In summary:
    • The optimal position for connecting a solar system inverter is typically as close as possible to the power meter to reduce AC wiring length and associated losses.
    • When an ATS is present, the solar inverter should generally be connected upstream of the ATS to ensure it can contribute power in both normal and backup modes.
    For detailed and specific guidelines, refer to the latest editions of IEEE 1547, NEC 690, and NEC 705, as well as the installation manuals provided by inverter manufacturers.
    "


    When asked: In which document and in which part of it did you get the information that the inverter should be connected upstream of the ATS ?

    ChatGPT replied:
    "The recommendation to connect the inverter upstream of the ATS (Automatic Transfer Switch) is not explicitly stated in a single standard document but is derived from best practices and general guidelines in industry standards and installation manuals."
    PLease find below our current design drawing (still in progress), so you can better understand the discussing.

    The only scenario I can imagine in which connecting the solar inverter downstream of the ATS would be advisable is if the solar inverter can operate in tandem with the generator. This configuration could reduce diesel consumption when the ATS switches from the mains to the generator. I cannot envisage any other situation where this setup would be recommended.
    Attached Files
    Last edited by doraimom; 05-19-2024, 08:23 PM.
    Tags: None
    • J.P.M.
      Solar Fanatic
      • Aug 2013
      • 14939
      #2
      Seems like the questions your asking ought to be asked of an engineering outfit with knowledgeable (as in licensed Professional Engineers ) in their employ.

      If nothing else, put yourself in your client's position: How would your client feel if they knew you were seeking professional help from a public forum where opinions and those who may give them are unvetted, mostly anonymous and as often as not, or at least possibly, uninformed and maybe/likely dangerous ?

      Get and pay for your engineering opinions from recognized and established sources.
      It'll be safer for all concerned, including you.
      Last edited by J.P.M.; 05-20-2024, 12:47 AM.
        👎 1

        Comment

        • doraimom
          Junior Member
          • May 2024
          • 3
          #3
          Originally posted by J.P.M.
          Seems like the questions your asking ought to be asked of an engineering outfit with knowledgeable (as in licensed Professional Engineers ) in their employ.

          If nothing else, put yourself in your client's position: How would your client feel if they knew you were seeking professional help from a public forum where opinions and those who may give them are unvetted, mostly anonymous and as often as not, or at least possibly, uninformed and maybe/likely dangerous ?

          Get and pay for your engineering opinions from recognized and established sources.
          It'll be safer for all concerned, including you.
          I appreciate you taking the time to share your personal opinion with us here.
          In my 40+ years of experience with technology-related forums, I have found that over 90% of the time, I receive valuable insights.
          Additionally, I am posting my questions in a specialized solar forum, where one would expect to find knowledgeable individuals in the field.

          Rest assured, as I am seeking technical references and standards, I'm certainly fully capable of assessing the relevance and value of the information I might receive.
          I do not consider everything posted in forums to be indisputable truth, but I do see significant value in consulting a broad technical community through web forums.

          Regards,

            Comment

            • Mike 134
              Solar Fanatic
              • Jan 2022
              • 393
              #4
              Sure is a small service. This for a housing development perhaps 100 homes?

              Just my 3 beer thoughts, if you're on generator likely it's weather related and not a bright sunny day.

                Comment

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