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  • Casey
    Junior Member
    • Aug 2022
    • 4

    Is Tesla D-rating my system too much?

    I've received a solar panel system from Tesla. they ​put a 11.2kw system with a 7.6 kw inverter.
    I've asked them to stack it with the 3.6 inverter.
    They said it's not a good idea because the 28 panels are divided into 4 group each group of 4 on their own electric string.. 3 groups of 8 panels are stringed to the inverter and 1 group of 4 panels also stringed to the inverter.
    They have it all on one inverter and will not divide the panels up amongst 2 inverters a 7.6kw inverter and a 3.6kw inverter. The system is already on the house. So if they take one string of 8 panels and run it through the 3.8 inverter. It would have an undersized 3.2 kw array of 8 panels on one string running to an 3.8 kw inverter and a slightly oversized 3 strings of an 8.0 kw array of panels, 2 strings of 8 panels and 1 string of 4 panels going to the 7.6 kw inverter. They are telling me this is a bad idea and that if I want it done I will have to pay for the inverter and install.
    And I am telling them that having my whole array of panels that face south east but slightly more south will be clipped too often with 7.6 kw inverter.
    I kind of have them in a bind because even though they've already installed the 28 panels on 4 separate string and will turn on with a flip of the switch it is just pending inspection. However, Tesla can not bill me or request Inspection yet as they are waiting permission from me to come back with a part they didn't have with them during install, the Nero that helps with metering and the phone app. In spite of that hold up the system is functional and turns on.
    They are offering a few alternative solutions.
    A: I can pay for the 3.6 kw inverter out of pocket. Out of pocket because there technical team say I don't need it
    B: I can pay for more panels until it meets their standard for another inverter to be stacked with the first.(The wife doesn't want any panels on the front of the house and the back is maxed out)
    C: They can draw up an agreement in which I will be guaranteed that there will not be an "unhealthy" amount of clipping of the energy produced by the inverter and if there was they would need to rectify it. I guess by adding an inverter. To which I told them how are we going to agree on what's a "healthy" amount of clipping?
    Can I please get advice on what I should do?
    I wish Tesla had like 9 kw inverter to install but they don't and I I've received a solar panel system from Tesla. they ​put a 11.2kw system with a 7.6 kw inverter.
    I've asked them to stack it with the 3.6 inverter.
    They said it's not a good idea because the 28 panels are divided into 4 group each group of 4 on their own electric string.. 3 groups of 8 panels are stringed to the inverter and 1 group of 4 panels also stringed to the inverter.
    They have it all on one inverter and will not divide the panels up amongst 2 inverters a 7.6kw inverter and a 3.6kw inverter. The system is already on the house. So if they take one string of 8 panels and run it through the 3.8 inverter. It would have an undersized 3.2 kw array of 8 panels on one string running to an 3.8 kw inverter and a slightly oversized 3 strings of an 8.0 kw array of panels, 2 strings of 8 panels and 1 string of 4 panels going to the 7.6 kw inverter. They are telling me this is a bad idea and that if I want it done I will have to pay for the inverter and install.
    And I am telling them that having my whole array of panels that face south east but slightly more south will be clipped too often with 7.6 kw inverter.
    I kind of have them in a bind because even though they've already installed the 28 panels on 4 separate string and will turn on with a flip of the switch it is just pending inspection. However, Tesla can not bill me or request Inspection yet as they are waiting permission from me to come back with a part they didn't have with them during install, the Nero that helps with metering and the phone app. In spite of that hold up the system is functional and turns on.
    They are offering a few alternative solutions.
    A: I can pay for the 3.6 kw inverter out of pocket. Out of pocket because there technical team say I don't need it
    B: I can pay for more panels until it meets their standard for another inverter to be stacked with the first.(The wife doesn't want any panels on the front of the house and the back is maxed out)
    C: They can draw up an agreement in which I will be guaranteed that there will not be an "unhealthy" amount of clipping of the energy produced by the inverter and if there was they would need to rectify it. I guess by adding an inverter. To which I told them how are we going to agree on what's a "healthy" amount of clipping?

    Can I please get any ones opinion what to do?

    ​Also They say I am going to get 202 percent of my energy needs but that I and my wife plan on getting electric vehicles in the future. And that was based off of 3 months of bills from the winter of a house I just moved into that runs off of natural gas in the winter and electricity for a.c.in the summer.
    I think the 7.6 kw inverter will be clipping the 11.2kw on too many days. I would have paid for a less panels if I knew ahead but they don't talk about the size of the inverter in the agreement we sign only that there will be an inverter.

    ​Also, Tesla is telling me to worry about it because I'm getting 202 percent of the energy that I need. But I say that's irrelevant because they are willing to sell me all the the panels I'm willing to buy yet want to not put in a inverter that supports them even though they don't make it clear in the contract what kind of inverter will be going with the system.
    Even though l, They say I am going to get 202 percent of my energy needs but that I and my wife plan on getting electric vehicles in the future. And that was based off of 3 months of bills in the winter of a house I just moved into that runs off of natural gas in the winter and electricity for a.c.in the summer.
  • OCJ
    Member
    • Aug 2022
    • 64

    #2
    So the first thing you need to do is quantify the clipping. That's going to require a bit of in-depth analysis on your part, but it's not too bad.

    You'll want to visit PVWatts and enter your system information. You'll need to break it up by different azimuths and tilts if they are different. You'll want to run it with DC to AC Size Ratio (under Advanced) of 1.0 to see what your full "potential" could be. I recommend downloading your monthly/hourly data so you can open it in Excel and dig down into the details.

    Next, you'll want to re-run the same thing with a DC/AC ratio of 1.47 (11.2 / 7.6). Now, it's actually closer to 7.7 but go ahead and use 7.6. Don't forget to download your monthly/hourly data.

    First, compare the two in annual performance. How much are you losing per year? Is that loss worth the additional cost of another inverter? What did Tesla say your annual production would be?

    Then, if you want, you can dig down into the hourly data and see when you would start clipping. That would be the hourly data with with the DC/AC ratio of 1.0. Anything over 7.7 would clip. You'll probably find that May-Aug is going to have some, but after September not so much if any at all.

    I'm at a 1.26 ratio. My system didn't come online until May so I saw a few days of clipping but by the time I got PTO hardly any. My system is SE, NE, SW, NW though.

    What you may find if yours is all SE is clipping in the morning but falling off later in the day. Hope this helps.

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