Does this site survey justify pointing the array way away from south?

williatywilliaty Solar Expert Posts: 60 ✭✭
in Advanced Solar Electric Technical Forum #1
We're at the point of actually needing to start setting anchors into the ground for our solar install here at our house. Unfortunately, I did the initial site survey mid-winter, guessing about the obstruction from vegetation and also guessing about where I'd actually be able to put anchors into the ground for the panel mounts. OUPS came out and marked the underground utilities today and my preferred site for the array is out of the question. In trying to find an alternative, I also realized I'd really missed a lot of obstructions in the winter due to lack of leaves. So given that I'm really constrained by where I can put anchors in the ground, there's one site where just looking around I could see a lot more sky than anywhere else. When I did a new survey (using Spyglass on iOS), I realized that due south is basically clobbered by 2 large cherry trees that are in a place I can't access to cut down. I've attached a chart that has the path of the sun through the sky each month vs the treeline. Given that the East sky isn't great, and the South sky is completely clobbered, it seems like the array needs to face southwest (roughly 225*) to maximize the clear sky available from the only location that's even slightly viable. However, "ignoring" half the day just feels really wrong if I'm trying to catch sun! What do you guys think of this?



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  • BB.BB. Super Moderators, Administrators Posts: 32,639 admin
    #2
    You might look at "virtual tracking"... 1/2 the array facing ~120 degrees, and the other half facing 210-220 degrees.

    Standard elevation (best year round) would be ~40 degrees from horizontal (your latitude). Roughly + or - 15 degrees for winter/summer optimization.

    You can use PVWatts and download the spread sheet data to play with the numbers and your hard shadow times (as well as play with tilt):

    https://pvwatts.nrel.gov/pvwatts.php 

    Can you raise the array off the ground by 20 feet (2 story)?

    And the other concern... Trees do grow both in width and height. They run the risk of blotting out more of your harvest in the future unless you can do something about them now.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Dave AngeliniDave Angelini Solar Expert Posts: 6,147 ✭✭✭✭✭
    #3
    Whatever you do, you need sun all day offgrid. No excuses that you will regret later. If it feels wrong to you, you know what to do.
    The good news is it is easy to do later as long as there is a place to locate it. Keep in mind that if you have to a long way out, you can use the 600vdc mppt's from Morningstar or Schneider. Good Luck!
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

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  • softdownsoftdown Solar Expert Posts: 3,609 ✭✭✭✭
    #4
    I do not believe that an array only pointing southwest will work with any satisfaction at all. BB pointed out a good solution.
    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
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