Inverter Selection for: 8.8KW Array

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  • jcgee88
    jcgee88 Solar Expert Posts: 154 ✭✭
    #32
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    Re: Inverter Selection for: 8.8KW Array
    cpetku wrote: »
    With regard to the trees, I had a solmetric report run and shading was estimated to be an issue on the bottom string in the winter. The Photo's I took indicate this may have been too optomistic. I really don't want to cut these down so we'll be monitoring the situation over the next few months.

    Similarly, my contractor used a Solar Pathfinder to project
    year-around shading. The Pathfinder suggested that the
    row of PV panels closest to an oak tree in front of my house
    would get shaded in winter, but that the rest would be fine.
    In actuality, the shading in winter is extending about 15 feet
    beyond what Pathfinder predicted, which in turn is affecting
    almost all the panels from 9 am to noon. This is causing probably
    a 25% overall loss for me. (There's no loss during the summer
    because the sun comes in far to the left of the tree.)

    Since the biggest amount of loss is during the months of lowest
    production, the dollars I'm losing aren't that much. But seeing
    the big dent in my production curve does drive me nuts! I
    sawed down two of the most offending upper branches...but
    I'm not really keen on continuing to trim an otherwise nice tree.

    Since you are using a central inverter, can you please report
    to us what happens to your overall production during times when
    you incur partial shading (like your picture #2)?

    John
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  • cpetku
    cpetku Registered Users Posts: 22 ✭
    #33
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    Recommendation

    I was kind of suprised that my installer never sent me an acknowledgement for this referral (I emailed him the file for his use) He did a good job, had a great price and was very professional in his conduct. That's what I was trying to get across, what do you guys think, should I have just done a simple letter?


    FYI: Removed Snow from panels using a broom on a 24' extension every day. Mostly overcast in January.
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #34
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    Re: Inverter Selection for: 8.8KW Array
    jcgee88 wrote: »
    Just to clarify on the terminology...

    There are two ways to speak of "strings":

    1. A physical grouping, for example, one set of PV
    modules on one roof and one set on another;
    2. A logical grouping, i.e., all panels that are connected to
    one inverter make up one string. The panels could be
    located on different facets of your roof, or have
    different angles, etc...they would still be considered part
    of "one string."

    I believe that the most widely accepted definition of a PV string is a set of modules connected electrically in series. A 36 module array could be (for example) 4 strings of 9 modules each. The physical placement of the modules is irrelevant. It's important to system performance, of course, but not to what is considered a string.
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  • cpetku
    cpetku Registered Users Posts: 22 ✭
    #35
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    Re: Inverter Selection for: 8.8KW Array

    Milestone days (looking like 1MW-H every 4-5 weeks),

    7/24 Crossed over 5MW-H of generated power.
    6/27 Crossed over 4MW-H of generated power.
    5/29 Crossed over 3MW-H of generated power.
    4/24 Crossed over 2MW-H of generated power.
    3/18 Crossed over 1MW-H of generated power.

    customer_chart.aspx?SID=f1630b5b08289ab4669ebf2c66bb1d0ecustomer_chart.aspx?SID=b799b6e1c64f7108c10e45c4f3d77bfbcustomer_chart.aspx?SID=33372dbca8f89a76130c7ab1b02f6ae0
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  • SpartanScott
    SpartanScott Solar Expert Posts: 41 ✭
    #36
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    Re: Inverter Selection for: 8.8KW Array

    Hi Mr. Petku,

    I'm glad to see that you were able to get a solar system installed. I'm always happy to see another solar system go live in Michigan. I am also happy to see that you were able to work with H.E. as your installer. Jeff has a quality group of men working installs for him.

    I'm interested in seeing how well your system sheds snow with the steep tilt? Do you have any pictures after the 12" blizzard we had Feb 2nd? If your system sheds snow well, then those trees will be more of an issue. Otherwise, the snowcover will cause more of an issue than the trees. For comparison, this winter I saw a 40% loss due to snow cover in the winter months with our installed systems with a 5/12 tilt.

    -Scott
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  • cpetku
    cpetku Registered Users Posts: 22 ✭
    #37
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    Re: Inverter Selection for: 8.8KW Array

    Hi Scott,

    I bought a 23' extension pole from the painting department at Home Depot and placed a lightweight shop broom head on it. I cleared the panels just about every monring before going to work. No pictures after any of the storms but in general I'd never have more than about 4" of snow on the panels regardless of the overnight percipitation. As long as I cleared the panels to avoid thaw and refreezing at the gap between strings, I never had a problem. In many cases the panels would have self cleared during the day, but being a new install I wanted to make sure the system was working right.

    Compating my system to yours, you have a much more symetrical generation profile. I have shading in the mid-morning but I am not willing to cut down all of the trees. That said, my generation this month has been about 1.55x yours if we can believe our data loggers (I think my Fronius logger is a little high at times). This reflects the shading issue since based on the size of the DC array it should be more like 1.6x. I'll let the trees live if the shading is really only 3%..

    Another unit in the area with 30 Enphase inverters (200w ea) occasionally outgenerates my 36 x 240 Watt Sharp panels. I'm not sure if this is due to shading or the cloud pattern, but I've been impressed by it. In my case I considered the steep roof angle to be a significant servicability issue for installing Enphase units. Even though they have good specs, I just don't trust any inverter to last more than sbout 12 years. The idea of replacing all of theose inverters as they fail or pre-emtively just didn't seem resonable in my case. Had I been ground mounted or a shallow pitch I would have gone that route.

    Looking at the different Electrical Panel loggers I decided to go with Brultech since they had the most data collection channels. I bought two of their boxes and instrumented over half of my panel getting the most critical loads. After a couple of weeks I was able to establish the cause of high bills. While I need to leave the refridgerator(s) and computer alone for now, I have changed the temperature profile for the hot tub to reduce demand on days where it is idle. I'd post a link to the energy reports but a weak point in their SW is I have to allow users access to the setup screen. I don't think this is a good idea, so here's a static image for those considering Brultech.

    Best wishes to M.M.S. and H.E.

    --Craig
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  • cpetku
    cpetku Registered Users Posts: 22 ✭
    #38
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    1st Year

    A little over 8MW generated over the course of 365 days on an 8.65KW array in mid-lower Michigan.

    I had originally estimated 9MW using SAM (NREL) but after tweaking the shading hours to align better with my location I'm tracking reasonably well over the course of a year.

    The Net Present Value with adjusted shading was around $7K for my location :D.

    In general this project made a lot of sense even though Michigan doesn't get near as much sun as the south or west coast.

    --Craig
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