Pier locations

MontanaCowboy Registered Users Posts: 1
Hello, new guy here and I'm thankful to have found your forum.
I own an off-grid ranch secluded deep on a Montana mountain.  We've been living on generators and battery banks/inverters (that charge from the generators) and I'm in the process now of installing a complete solar power system.  Since I'll never be able to eliminate generators completely (for farm equipment/welders/etc.) I bought a system just to meet the needs of my house to at least eliminate running generators at night (after awhile you can hear them running even after you turn them off!).

I ended up purchasing the 4.43kw "Homesteader" package from Wholesale Solar (https://www.wholesalesolar.com/1891300/wholesale-solar/complete-systems/the-homestead-4.43-kw-15-panel-solarworld-off-grid-solar-system ).  After much comparison, I came to believe that this is a well engineered system but I'm certainly no expert which brings me here to this forum in search of assistance.  The salesman Jeremy Allen is clearly knowledgeable and courteous and is willing to assist with specific questions.  The trouble is, I don't possess the skill set yet to know what questions to ask.  I own a commercial refrigeration and welding company, and I've worked as a Journeyman electrician and certified welder (both pipe and structural), but the specifics of solar power are new to me.  My only complaint with the system from Wholesale Solar (at this point, at least) is that the accompanying instructions absolutely suck!  There is no step by step detailed instructions on how to install their system and they instead refer you to the manufacturer websites of the individual components in most cases and I find this unacceptable.

This is my cabin.  The red square in on the hillside is where I plan to install my solar panels (the small solar panels in the picture no longer work).  The hillside faces almost perfect true south and around a 45 degree incline (being near the 46th parallel, I need a 46 degree slant as I understand it).  I want to begin sinking my piers, but I'm having difficulty determining spacing and true square.  The Wholesale Solar website refers me to the Iron Ridge website, and the Iron Ridge website appears to assume previous working knowledge of installing solar panels.

Perhaps I'm just overwhelmed with pieces, parts and stacks of papers and cannot see the answers that should be directly in my face.  Any advice on setting my piers would be much appreciated.  The CAD drawings assume level ground so the front to rear spacing would be different than when mounted into a hillside if measured laterally across the ground.  I suppose I could extend the first level of piers upward and measure level across the top, but am hoping there is a commonly known geometric formula to simplify my measurements.  Any other advice and recommendations appreciated.


  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    I would set up a series of corners and strings near the ultimate flat plane of the racking. The piers will have varying heights above ground level (but the same absolute height), and ground will have whatever slope. Even on prairie, there is no such thing as perfectly level ground.

    Level and square the strings to establish the pier locations. The only formula is the sum of squares, or 3-4-5. A right angle is square if the long side of a triangle formed with the corner is equal to the square of the length of the other two sides. Practically, 3x3=9, 4x4=16, 16+9=25. If the long side of the triangle is 5x5=25, the angle is square. A cheap laser level is handy to establish level.
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    edited September 2017 #3
    Having worked as an electrican, you should be no stranger to unistrut, very handy, extremely ridged, adjustable setup, kind of like a Mechano set. My findings are it's easier to build the entire structure in a shop, move to the site, then dig holes, I made separate frames, each supporting 3 panels, for ease of moving to location. This was much easier than my first array, which was one large welded structure, the second was bolted, I found welding tends to distort the steel due to heat. Using slotted unistrut 45° brackets for triangulation would mean less drilling and adjustable to boot using bolts and spring nuts, I didn't have the luxury of unistrut due to unavailability, but would have use it, if it were available. Triangulation dramatically improves strength and rigidity. In my case the ground is level so placement was simply placing on the ground, leveling then pouring concrete into a 6" form encasing the legs, which had feet welded, so the entire array is on a slab, weeds don't grow on concrete, in the tropics if left on open ground the weeds would completely cover the array if left unchecked. Just sharing ideas FWIW.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,442 admin
    Is the hill stable? If not, you could need to go pretty deep for pier footings/columns. The few trees I could make out, seem to indicate the slope is stable--You don't see any trees that are "bent" at the base (hill moved after tree started growing)?

    Image result for trees on moving hill bent at base
    1024 × 768 - biology.stackexchange.com

    Beautiful country there.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
    Good point Bill, I thought it might be a man made hill when grading for the cabin.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • peakbaggger
    peakbaggger Registered Users Posts: 16 ✭✭

    A few comments. A 45 degree slope may be optimal for production but a PITA for snow accumulation. Plan on having to shovel off the array and that means leaving plenty of space at the lower edge of the array to let snow accumulate on top of your local snow pack. So if you have 4 feet of snow pack you probably want that lower edge 3 to 4 feet above that. If you get that much snow you probably have a deep frost line so you also need to go deep to get below the frost line. You could put in some real stiff pipe columns but it make a lot more sense to put in some reasonably sized posts and then put in diagonal bracing to stiffen things up. You can drop the array lower to the ground but it means you will need to shovel out in front of it. My pole mounted array was upgraded with larger panels at one point and the lower edge is too close to the ground with winter snow so I need to run my snowblower past it on occasion before I get a big frozen lump that covers the lower edge of the panels. Given that potential height if you have livestock it may be worth lifting it up bit higher and using it for shelter for the animals (make sure you have your grounding done right).  

    The alternative some folks use in snowy climates is to go with far steeper panels. Most people use more power in the winter than in summer (unless you need AC) so optimizing for more winter production may be desirable. Snow is a real good reflector and panels are more efficient when its cold so going with steep almost vertical panels will maximize your winter production (realize the short number of daylight hours still really makes a dent in production). On occasion folks will just hang them vertically off the side of barn or other accessory building. The down side is the production is poor in summer. 

    The ideal alternative is setting up panels with adjustable angles. I have two small arrays, a wall mounted one and pole mount that both can be adjusted for winter and summer angles. I cant go vertical but I can adjust in a range between 30 degrees and 60 degrees (I am just below 45 degrees latitude). This obviously requires more complexity but given your trade I expect its something you can figure out. My pole mount is balanced on a center pivot so changing the angle takes me about 5 minutes. The wall mount requires a wooden pole and hydraulic jack to move it around, it takes me about 15 minutes with most of it set up time as I leave the pole all set up in the garage. I still can get snow buildup as Northeast snow can be wet and sticky but a steep angle cuts it way down and usually they will self clear. I actually adjust them a couple of times a year, I adjust to winter angle in early November, then crank them up to 45 degrees in late march and then go to summer angle in late april, then crank them down in late August.

    Be aware that rarely do off the shelf designs factor in unusual wind loading. If you elevate the array you need to factor in peak winds. That usually means lots of bracing and adequate footings. Generally the panels are well attached to the rails but it wouldn't hurt to go a bit generous on attachment clips. Usually what fails is the underlying structure, through bolts are far preferable to screws and nails.