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Are there limitations for stacking grid-tie inverters?

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  • Are there limitations for stacking grid-tie inverters?

    Or can these, with the proper power purchase agreements, etc. theoretically go infinite?

    For example, could I buy a bunch of the below inverter and stack up to 160 [kW] in parallel (for selling back to the grid), or do I need to find a model that specifically says the grid-tie inverter is stackable up to X kilowatts?

    https://www.wholesalesolar.com/29610...0-208-inverter

  • #2
    There is no limitation on the inverters themselves, but there will be considerations in how they are wired and in your interconnect agreement with the power company. At some point, as your system gets bigger, it would be more practical to consider higher voltage three phase inverters.
    CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

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    • #3
      Originally posted by sensij View Post
      There is no limitation on the inverters themselves, but there will be considerations in how they are wired and in your interconnect agreement with the power company. At some point, as your system gets bigger, it would be more practical to consider higher voltage three phase inverters.
      Thank you, that is great to hear! Are higher inverter output voltages more difficult to connect with the grid (once the interconnect agreement with the power company, etc. gets taken care of)?

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      • #4
        Originally posted by TheMechE View Post

        Thank you, that is great to hear! Are higher inverter output voltages more difficult to connect with the grid (once the interconnect agreement with the power company, etc. gets taken care of)?
        I'm not sure what you consider difficult. As system size goes up, the interconnect agreements get more complex. The grid is not an infinite power sink, larger systems require more extensive planning.
        CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

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        • #5
          Originally posted by TheMechE View Post

          Thank you, that is great to hear! Are higher inverter output voltages more difficult to connect with the grid (once the interconnect agreement with the power company, etc. gets taken care of)?
          This is a school project, right ?

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          • #6
            The feed lines from the utility to your house become a limiting factor, both in current handling capacity and because of voltage rise on your house side - tripping inverters off line from over voltage
            Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
            || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
            || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

            solar: http://tinyurl.com/LMR-Solar
            gen: http://tinyurl.com/LMR-Lister

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            • #7
              Originally posted by TheMechE View Post
              Or can these, with the proper power purchase agreements, etc. theoretically go infinite?
              There are finite limits for how many of a single type of inverter you can stack. (I believe Outback limits GVFX stacking to eight, for example.) However, to the question I think you are really asking, there's no limit to how much DC from a solar array you can convert to AC, given sufficient grid interconnect capacity. There are several 500+ megawatt PV plants out there.

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              • #8
                The utility interconnection process is usually the ultimate limiting factor. In order to encourage PV most utilities have a maximum size limit (My state is 10 KW) before a interconnect study is required. The rules for selling power also get far less attractive depending on the market. The utility does an interconnect study and depending on the proposed system size they may need to upgrade a lot of equipment on their end which you get to pay for. Most older utility stations are designed to bring in power from the grid and distribute it to local circuits, it may not have the protective relaying in place to protect the grid from power being generated and sent out to the rest of the grid so they need to upgrade the substation on your dime. The utility is also concerned with what happens if the grid goes down and your system is still trying to push power into the grid so they may require a Direct Transfer Trip circuit to guarantee that if the grid goes down or they just plain don't want you to generate that they can reach into your system and turn off the output. These upgrades can be well over 100K with 300K not unusual. It can go much higher if the higher voltage distribution needs upgrades. The regional transmission organization may also want to keep and eye on what is going on so add in more bucks to give them access. This process can take many months or years and can kill projects.
                Last edited by peakbagger; 09-12-2017, 05:38 PM.

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                • #9
                  Originally posted by jflorey2 View Post
                  There are finite limits for how many of a single type of inverter you can stack. (I believe Outback limits GVFX stacking to eight, for example.) However, to the question I think you are really asking, there's no limit to how much DC from a solar array you can convert to AC, given sufficient grid interconnect capacity. There are several 500+ megawatt PV plants out there.
                  Does that finite inverter limit apply to the inverter I pointed out though? I've noticed some grid-tie inverters just don't specify a limit.

                  Originally posted by J.P.M. View Post

                  This is a school project, right ?
                  Yes
                  Last edited by TheMechE; 09-12-2017, 07:56 PM.

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                  • #10
                    Originally posted by TheMechE View Post
                    Does that finite inverter limit apply to the inverter I pointed out though? I've noticed some grid-tie inverters just don't specify a limit.
                    Two issues there.

                    1) You can use as many of them as you like (to the limits of the grid interconnect rules you operate under) but they are not "stackable" in the way some other inverters are, where several inverters are synchronized through a specific interface. The inverters you list have no need of such synchronization; they will feed back power to the grid whether they are next to each other, on separate homes, or 100 miles away from each other. No explicit coordination is needed.

                    2) When you are going to larger systems, staying with single phase inverters is generally a mistake. Three phase inverters continuously convert power from AC to DC; single phase inverters of the type you list can only convert while the grid voltage is nonzero. That means they have to stop converting 120 times a second; they store the energy from the panels during this time in capacitors, and capacitors are both somewhat expensive and a significant failure item (they tend to dry out and stop working after a while.)

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                    • #11
                      Note also that the data sheets and marketing materials list various standards that the units meet, including some UL standards, but do not anywhere explicitly state that they are UL listed and therefore legal for installation in the US.
                      SunnyBoy 3000 US, 18 BP Solar 175B panels.

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