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    Solar - Generator connection

    I get an email yesterday asking me if I will go out and inspect a generator/solar installation. They were not sure if it was hooked up correctly by the generator installers. The generator was installed after solar. City inspection - passed. POCO review of installation - passed. Took me a few minutes since I have hardly done any solar work to figure out what was wrong. The load center is inside behind the meter and ATS.

    Not sure how they didn't have problems. Been in for about 3 years I belive.

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    #2
    Most likely they have not had problems because there has never happened to be an outage or load test of the generator while the PV was producing and the active local load was less than the the PV output.
    If there was never a reason for the GTI to try to backfeed the generator, there would be no symptoms.
    That or the generator output did not meet the 5 minute stability and precision test for the GTI to lock on and start producing.

    Comment


      #3
      Where is the pv connection relative to the generator connection? I assume you are getting at that the pv is on the load side of the generator? I know it's wrong, and I wouldn't try it, but probably the inverter would shut down before any damage was done.
      Ethan Brush - East West Electric. NY, WA. MA

      "You can't generalize"

      Comment


        #4
        Originally posted by electrofelon View Post
        Where is the pv connection relative to the generator connection? I assume you are getting at that the pv is on the load side of the generator? I know it's wrong, and I wouldn't try it, but probably the inverter would shut down before any damage was done.
        Not necessarily. I used to teach an off grid lab with a Sunny Boy, Sunny Island, and Generac genset. The SB ran just fine with the genny as the "grid".

        Comment


          #5
          Array > inverter > load center < ATS < POCO/Generator is the arrangement.

          Comment


            #6
            Originally posted by ggunn View Post
            Not necessarily. I used to teach an off grid lab with a Sunny Boy, Sunny Island, and Generac genset. The SB ran just fine with the genny as the "grid".
            I remembered you said that in a previous thread - hence, I didnt say the inverter would not synch to it What I said was the inverter would likely shut down before any damage was done. That is, even if the inverter did synch up to the genny, if demand went below production, the inverter would drive up frequency and/or voltage and THEN shut down. That is my hypothesis anyway. Anyone want to take one for the team and try it?
            Ethan Brush - East West Electric. NY, WA. MA

            "You can't generalize"

            Comment


              #7
              Originally posted by electrofelon View Post
              I remembered you said that in a previous thread - hence, I didnt say the inverter would not synch to it What I said was the inverter would likely shut down before any damage was done. That is, even if the inverter did synch up to the genny, if demand went below production, the inverter would drive up frequency and/or voltage and THEN shut down. That is my hypothesis anyway. Anyone want to take one for the team and try it?
              Just on theory, it would be the generator that would drive up frequency, and the inverter that would drive up voltage. Right?

              Comment


                #8
                Originally posted by electrofelon View Post
                I remembered you said that in a previous thread - hence, I didnt say the inverter would not synch to it What I said was the inverter would likely shut down before any damage was done. That is, even if the inverter did synch up to the genny, if demand went below production, the inverter would drive up frequency and/or voltage and THEN shut down. That is my hypothesis anyway. Anyone want to take one for the team and try it?
                I think it would be a race. I wouldn't count on the inverter shutting down before frying control circuits in the generator.

                Comment


                  #9
                  Originally posted by ggunn View Post
                  I think it would be a race. I wouldn't count on the inverter shutting down before frying control circuits in the generator.
                  But the inverter would shut down at what, 63 hz? I would conjecture that the inverter operation window is a lot less than the generator "damage window." Like I said, I am, not going to try it.
                  Ethan Brush - East West Electric. NY, WA. MA

                  "You can't generalize"

                  Comment


                    #10
                    Are there any code issues? Or are they just operational?

                    Comment


                      #11
                      Originally posted by Chamuit View Post
                      Are there any code issues? Or are they just operational?
                      I am not aware of any direct code violation. If there is, I would guess it would be in 702 or 705. Note that this would be perfectly fine with the right equipment and/or controls.
                      Ethan Brush - East West Electric. NY, WA. MA

                      "You can't generalize"

                      Comment


                        #12
                        Originally posted by electrofelon View Post
                        I am not aware of any direct code violation. If there is, I would guess it would be in 702 or 705. Note that this would be perfectly fine with the right equipment and/or controls.

                        Thanks. I didn't see anything that would prohibit the hook up to be arranged that way. I did call Generac and they said that the unit attach is not designed to work with solar. They do have models (controllers) that would work with solar like this.

                        Comment


                          #13
                          Somewhere in 705 it says that interactive sources must be 'compatible'. One could make the case that is a violation here.

                          Comment


                            #14
                            There's nothing in the NEC that says you can't connect a generator in parallel with a PV system, which is good because there are cases where it is the desired design. Remember 90.1(B), the purpose of the code is safety, not keeping the equipment working. That's the job of the system designer or engineer.

                            Having a generator and PV in parallel is not a guarantee that one will damage the other, it just creates the condition under which one can damage the other. Under the right conditions these two can get along fine, but those conditions are not usually maintained if they are not designed in.

                            Comment


                              #15
                              Originally posted by pv_n00b View Post
                              There's nothing in the NEC that says you can't connect a generator in parallel with a PV system, which is good because there are cases where it is the desired design. Remember 90.1(B), the purpose of the code is safety, not keeping the equipment working. That's the job of the system designer or engineer.

                              Having a generator and PV in parallel is not a guarantee that one will damage the other, it just creates the condition under which one can damage the other. Under the right conditions these two can get along fine, but those conditions are not usually maintained if they are not designed in.
                              Well said. For example, a Sunny Boy, Sunny Island, and generator system can work really well off grid because the SI arbitrates between the SB and the genny, throttling back the SB when the batteries are full and the loads are less than the available output from the SB.

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