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Roof mounted vs ground mounted solar array

Discussion in 'Tesla Energy' started by sunnyfield, Jul 10, 2018.

  1. sunnyfield

    sunnyfield Member

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    #1 sunnyfield, Jul 10, 2018
    Last edited: Jul 10, 2018
    Obviously most people go for roof mounted, I'm just wondering what the experience has been like for those of you that went ground mounted. My wife and I are considering going ground mounted so we can have a larger array than our rear roof will allow, but we're not sure if it has some unintuitive drawbacks. The main issue I can think of is that Maine gets a bit of snow in the winter months, so it'll require shoveling to prevent the snow from piling up at the bottom.

    Also, has anyone leveraged automatic tilting panels? Probably not leaning that way, but they look cool.
     
  2. Gwgan

    Gwgan Almost a wagon

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  3. sunnyfield

    sunnyfield Member

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    Thanks for sharing this! That is an incredible difference! How far away were you able to make the clearing? My wife would prefer we put it in a clearing that isn't visible from the house (with trees in between), but I'm sure it's cost prohibitive to run it 400 or 500 feet underground. The AllEarth Solar Tracker looks incredibly impressive.

    Also just a quick question since I noticed you're also in Maine, what are you using for heating?
     
  4. BerTX

    BerTX Supporting Member

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    Tracking is cool, no doubt. From an economic standpoint, you are much better to spend less money and get more panels in most cases if you have space.

    I know nothing about dealing with snow. I don't like the stuff and avoid it.

    I could have put panels on the roof, but like having them on the ground so I can clean them. I also adjusted the angle of them this year, and that wouldn't have been easy on the roof. Putting them on the ground may require gravel underneath or something to stop vegetation growth. Birds like to sit on mine and eat (and poop out) seeds, I guess. I get all kinds of odd plant growth that occurs nowhere else on the property, including saplings growing up through the array.
     
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  5. AudubonB

    AudubonB Mild-mannered Moderator Lord Vetinari*

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    #5 AudubonB, Jul 10, 2018
    Last edited: Jul 10, 2018
    I have 44 panels on the roof, just took down 4 on a tracker that were 65’ up on a tower, and have 18 on the ground that are about to be joined by another 18, so I think I’m qualified to present some information.

    Also, we’re at 63ºN latitude....

    1. The original ground mounts are on a tiltable rack. I didn’t fab those...unfortunately, I guess, as it’s a telspar-based system wherein a 2” spar fits into a 2 1/4” spar....

    It does NOT work well: I have to perform the adjustments either with my excavator bucket or tallest forklift, otherwise, if I try to perform them manually (one support at a time, of course), they’ll rack and go kaflooey - FORTUNATELY, I determined that the diminution of solar gain during our summer, were we to keep the angle at winter-max, was negligible so that is exactly what I do: keep it now permanently at the steepest winter angle. If that is so at 63º, it certainly also will be so at Maine’s 45º or so latitude.

    This should lower the capital costs enough to make a nice little difference (and with the 18 new ones I’m working on right now I am, of course, not providing any adjustability).

    2. The ground-mount is just over 300 feet to the control center. Yes, cable is hellishly expensive. I was super-lucky to snag some 660 feet of 3/0 armored copper cable from the Fort Knox gold mine north of Fairbanks, otherwise I’d have needed my own Fort Knox to pay for it. If you're 400-500’ away.....ouch. You may need to go to Plans B, C or X.

    3. Trackers: To a great extent, the increase in gain from a tracker is, nowadays, NOT justified by the price of a tracker. If you want 30% (or whatever) more solar electricity, buy 30% more panels....that’s cheaper than the tracker. This is a shame, as trackers are so compelling, but. Of course, other constraints may dictate that 30% more panels cannot be emplaned, in which case you can make an effective argument for a tracker.

    That said, does anyone want to purchase a gently-used tracker? Fully functional; this is a non-motorized one: boiling refrigerant moves from one side of the tracker to the other as the sun hits a radiator. Works great at -56ºF and +84ºF (the range it encountered when I had it installed). It’s a Zomeworks....don’t know the model. Make a bid.

    Lastly: snow. The bottom edge of my ground mount panels are about 4’ off the ground. This is NOT sufficient - by late April there always is a huge snow bank obscuring the lowest panels. Some time this summer I’m going to carve away at the ground in front and provide another 2 feet or so of room for the snow to accumulate. Also, I’ve heard of a spray-on product, used on airplanes, to make the panels’ glass more slippery and ease the snow off. Am extremely interested to try it.
     
  6. TomDiego

    TomDiego Member

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    I live in San Diego, exact opposite corner of the country from you, and we installed a 6.3kW ground mount solar array in April 2016. We live on an acre of land, most of it undeveloped, and we have a hillside behind and below the house that was nearly the optimal angle for a ground mount system, pointing almost due south-southwest. Except for Dec-Feb with the fewer solar hours and rain, we produce more than enough to power the 4 bdrm, 2.5 bath, 2137 sq. ft house during the day, fill the 2 Tesla Powerwall 2 batteries, and send energy back to the grid. The most recent exception was the 100*+ days we had the last few days, where the A/C has been running almost constantly 24/7, which has eaten up more than the solar can produce, thus reducing excess energy to the Powerwalls and requiring us to draw from the grid.

    Ground mount arrays are more expensive than roof mount solar, because of the necessity of installing fence posts in concrete footers and a more robust railing system, and the trenching necessary to go from the array to the house, and possibly conduit to get to the main panel. In our case, the array is mounted on the farthest side of the house from the main electrical panel, so it required conduit up to the attic on one corner of the house, across the attic, and back out to the main panel on the opposite side of the house. The advantage is that the panels can be aimed at the optimum angle, producing more power from fewer panels.

    Full details of our installation, including pictures, can be found on my public Enphase Enlighten site: Enphase Energy - Enlighten | Sign in to Enlighten.
     
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  7. nwdiver

    nwdiver Active Member

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    Why 3/0? I helped install 27kW of solar and we just ran each string independently with #10 ~220'. Yeah... that's 16 lines of #10 but that was 96 panels and 16 strands of #10 is half the price of 2 strands of 3/0...
     
  8. AudubonB

    AudubonB Mild-mannered Moderator Lord Vetinari*

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    It’s not half the price when the 3/0 was free.....:)
    A little more seriously:

    1. Did you test the real-world DC voltage drop along that 220’ of #10? Can it really be within acceptable limits? I’d be delighted to learn if so.

    2. Did you run the 16 lines in conduit? If so, what diameter will accommodate that many? I’m using 1.5” sliptube - great stuff to use over very long lengths, but I’m not sure how much #10 I can jam in there.

    3. Wait a minute: your job was -

    96 280W panels
    16 strings
    “hot” & “neutral” means 8 legs
    Divided into 96 means one pair of lines per each 12 panels. So 3.3kW per each #10 line. Can that be correct?
     
  9. nwdiver

    nwdiver Active Member

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    #9 nwdiver, Jul 11, 2018
    Last edited: Jul 11, 2018
    Yes. 16 #10 run in conduit (2" IIRC). <8A per string at ~400v so yeah ~3.3kW per string. I've not measured the voltage drop directly but I have visibility of system voltage and it appears acceptable... The great thing is that on good days the inverters are maxed out at peak so line losses are free :)
     
  10. wwhitney

    wwhitney Member

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    Random Internet voltage drop calculator says that #10 copper, one way length of 220', and 8A gives a voltage drop of 3.5V, so less than 1% at 400V.

    Cheers, Wayne
     
  11. ElectricTundra

    ElectricTundra P85D AP1

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    For a group home in Minnesota we split panels between roof and ground. We were thinking to keep the panels 4-5' off the ground to avoid snow problems and then decided to raise them a bit more, lay some pavers below them, and make a nice pergola for people to sit under. So in some ways our ground system became a sort of roof system.

    We've also done veggies, herbs and fruit/berries as well as ornamentals that do well in the shade under panels to avoid wasting space.
     
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  12. SKRGO

    SKRGO Member

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    Try this Nano coating, it was designed for solar panels that get covered with dirt and made cleaning a breeze. Make sure the panels are cleaned with a high proof alcohol before applying. This should work to keep snow from sticking also does well on Tesla Windshield and Pano glass. ;)

    Products


    I am note connected with this company.
     
  13. AudubonB

    AudubonB Mild-mannered Moderator Lord Vetinari*

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    I’ve got some 151º in the back of the liqu.....

    Oops! All gone!
     
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