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    Utility Co. limiting system size in Missouri

    I have a customer that was wanting to install a 30kw system on his home that is 10,000 square feet or so with an indoor pool. This system has been sized to only cover the usage of the home as the utility co. only does credits (monthly true-up) at avoided cost. The engineer at the utility co told him that "he could only do a 10kw system size because his home is at the end of the line". "Because the house was at the end of the line, any power produced but not used during the day would have to be "pushed" back through the line they came from. They max they would allow was 10KW so it wouldn't damage other houses". That was from the engineer. Also, said something about a lot of solar being in the area because of a neighbors solar panels.

    This is the first time I have ever came across something like this. Figuring a 30kw system might be feeding back 125A (probably 100A with inverters at a 1.2 DC/AC ratio) I do not understand how this could be an issue for the utility co? What am I missing? I have had systems limited by the utility co. in other states (KS) but never one in Missouri in my 12 years of being in the solar industry. I assume this would be something that would be in the statewide net metering laws/policys I might need to check in to?

    #2
    Originally posted by Dwest20 View Post
    I have a customer that was wanting to install a 30kw system on his home that is 10,000 square feet or so with an indoor pool. This system has been sized to only cover the usage of the home as the utility co. only does credits (monthly true-up) at avoided cost. The engineer at the utility co told him that "he could only do a 10kw system size because his home is at the end of the line". "Because the house was at the end of the line, any power produced but not used during the day would have to be "pushed" back through the line they came from. They max they would allow was 10KW so it wouldn't damage other houses". That was from the engineer. Also, said something about a lot of solar being in the area because of a neighbors solar panels.

    This is the first time I have ever came across something like this. Figuring a 30kw system might be feeding back 125A (probably 100A with inverters at a 1.2 DC/AC ratio) I do not understand how this could be an issue for the utility co? What am I missing? I have had systems limited by the utility co. in other states (KS) but never one in Missouri in my 12 years of being in the solar industry. I assume this would be something that would be in the statewide net metering laws/policys I might need to check in to?
    Some cooperatives (most) don’t allow net metering.
    We have limits on solar production also. You sized the system for their maximum use. What about when they aren’t using anything?
    many utilities do not want to push back on the transmission, and there are limits to how much the wire will carry.
    we recently had a metering point feeding two substations that went to 0 kW.
    theres only 10MW of Solar on this metering point. It was a very sunny day with temperatures around 68. We are mostly residential on these two stations.

    Have no clue how it could damage other houses, you sure this was an engineer or a service tech that worked in the engineering dept. there’s a big difference.

    Comment


      #3
      This home has a 400A service, the system (on paper) could produce 125A. So if the home was not using anything then their could be 125A on the conductors that are rated for 400A, that part is all good. I am not sure what other factors they might be looking at, maybe the amount of homes/load between the solar and the substation? This homeowner mentioned the name of the Engineer he spoke with whom is the head engineer for the utility.

      Comment


        #4
        10kW is an awfully round number. Makes me suspicious that they just have a rule and are making up BS to justify it in this case, especially if the customer's house routinely uses 30kW of load. That said, utility transformers aren't sized for load the way NEC covered components are. So maybe their line just isn't up to snuff. And if there's no law that requires them to upgrade it, then I suppose you're SOL.

        There are voltage rise effects with solar that could conceivably raise the voltage to a point where it could be higher than ideal in other houses. But in at least some of those examples the inverters would trip off first. The 'end of the line' argument makes little sense to me in this respect, although it maybe correct that if you installed 30kW it just wouldn't work most of the time.

        Comment


          #5
          I have installed systems larger than 10kw on this utility in the past.

          Comment


            #6
            Originally posted by jaggedben View Post
            10kW is an awfully round number. Makes me suspicious that they just have a rule and are making up BS to justify it in this case, especially if the customer's house routinely uses 30kW of load. That said, utility transformers aren't sized for load the way NEC covered components are. So maybe their line just isn't up to snuff. And if there's no law that requires them to upgrade it, then I suppose you're SOL.

            There are voltage rise effects with solar that could conceivably raise the voltage to a point where it could be higher than ideal in other houses. But in at least some of those examples the inverters would trip off first. The 'end of the line' argument makes little sense to me in this respect, although it maybe correct that if you installed 30kW it just wouldn't work most of the time.
            We limit our large ones to 2 MW per site now. Homes not so much.
            Honestly, if we had someone that wanted to install a 30kW system, we would say go for it...
            pat 7200V that’s less than 5 amps at full production.
            I don’t see why that limit is there.

            Comment


              #7
              Originally posted by jaggedben View Post
              1
              There are voltage rise effects with solar that could conceivably raise the voltage to a point where it could be higher than ideal in other houses. But in at least some of those examples the inverters would trip off first. The 'end of the line' argument makes little sense to me in this respect, although it maybe correct that if you installed 30kW it just wouldn't work most of the time.
              That is my assumption that these limits are for voltage regulation reasons, not for current reasons. I could see a line with a lot of DG needing to have voltage regulators reconfigured. Perhaps one of the utility guys like Hv&Lv can comment on that. I suspect sometimes these limits reflect legit engineering concerns, and other times they are due to solar unfriendly POCO's.
              Ethan Brush - East West Electric. NY, WA. MA

              "You can't generalize"

              Comment


                #8
                Originally posted by electrofelon View Post

                That is my assumption that these limits are for voltage regulation reasons, not for current reasons. I could see a line with a lot of DG needing to have voltage regulators reconfigured. Perhaps one of the utility guys like Hv&Lv can comment on that. I suspect sometimes these limits reflect legit engineering concerns, and other times they are due to solar unfriendly POCO's.
                Normally the invertors are voltage following. I’ve never had one “run away” with crazy voltage. Besides, don’t they trip out about 126 anyway?
                as far as the regulators, there are settings in the regulator control panel that is specifically for solar, or any other generation.
                If the relay is set to bi-directional like some people do, the regulators will continue to rise until it trips the invertors off(126V)

                The utility regulator relay needs to be set at cogeneration. This will keep the regulator at a steady voltage if it senses reverse current. All the newer popular SEL, Siemens MJs, Cooper, etc. have the setting that accounts for that.
                even the worst Siemens MJxL had something for it.

                Comment


                  #9
                  Originally posted by Hv&Lv View Post

                  Normally the invertors are voltage following. I’ve never had one “run away” with crazy voltage. Besides, don’t they trip out about 126 anyway?
                  as far as the regulators, there are settings in the regulator control panel that is specifically for solar, or any other generation.
                  If the relay is set to bi-directional like some people do, the regulators will continue to rise until it trips the invertors off(126V)

                  The utility regulator relay needs to be set at cogeneration. This will keep the regulator at a steady voltage if it senses reverse current. All the newer popular SEL, Siemens MJs, Cooper, etc. have the setting that accounts for that.
                  even the worst Siemens MJxL had something for it.
                  What I was envisioning is a line that wasnt designed with any consideration for DG. They might have assumed some base line voltage drop and have that be the lowest tap setting. Now DG comes along and that assumed VD is now gone, or perhaps even going the other way and the system cant compensate. As JB also noted, yes the voltage can only go so high until the inverters trip off, but that is 262 I think for 240 nominal which is pretty high. If I were a utility I would want a customer seeing 130/260.
                  Ethan Brush - East West Electric. NY, WA. MA

                  "You can't generalize"

                  Comment


                    #10
                    Originally posted by electrofelon View Post

                    What I was envisioning is a line that wasnt designed with any consideration for DG. They might have assumed some base line voltage drop and have that be the lowest tap setting. Now DG comes along and that assumed VD is now gone, or perhaps even going the other way and the system cant compensate. As JB also noted, yes the voltage can only go so high until the inverters trip off, but that is 262 I think for 240 nominal which is pretty high. If I were a utility I would want a customer seeing 130/260.
                    On our 2-10MW systems we have our own relay that I have set to monitor the voltage tighter than the invertors. (59)

                    kind of of a crappy system if it can’t compensate for that small of a backfeed...

                    Comment


                      #11
                      Originally posted by Hv&Lv View Post

                      On our 2-10MW systems we have our own relay that I have set to monitor the voltage tighter than the invertors. (59)

                      kind of of a crappy system if it can’t compensate for that small of a backfeed...
                      True. Some of these max values I hear, like the OP's I have a hard time seeing it being anywhere near an issue.

                      What are your distribution voltages?
                      Ethan Brush - East West Electric. NY, WA. MA

                      "You can't generalize"

                      Comment


                        #12
                        Originally posted by electrofelon View Post

                        True. Some of these max values I hear, like the OP's I have a hard time seeing it being anywhere near an issue.

                        What are your distribution voltages?
                        12.47 & 24.94
                        (7200 & 14400)

                        Comment


                          #13
                          Originally posted by electrofelon View Post
                          If I were a utility I would want a customer seeing 130/260.
                          Would, or wouldn't?

                          Comment


                            #14
                            Originally posted by ggunn View Post
                            Would, or wouldn't?
                            Ethan Brush - East West Electric. NY, WA. MA

                            "You can't generalize"

                            Comment


                              #15
                              It sounds like they’re being overly conservative or not wanting to run a real load flow study. In theory enough resi DG could cause backfeeding, voltage flicker, thermal overload, etc.

                              In reality it’s hard for me to see that occurring at the 10kW level. Aggregated DG issues are something we do run into with C&I and multimegawatt distribution connected projects. But Most utilities near us allow up to 25KW to be connected without significant studies or upgrades.


                              Sent from my iPhone using Tapatalk

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