PT Wood + Iron Ridge Design

[karamazov]

Ok so I have done a ton of research and browsing of various threads on this forum, probably for a good two weeks now. I am in the process of installing a 36 panel bifacial array that will be ground mounted in the pasture next to my house near my utility pole, which is where my equipment shed will be.

My thoughts leading up to this design, based on all the research are basically:
- all metal designs/kits are way too expensive for me (says the guy who bought 18kW of panels...)
- mounting panels directly to wood is probably not a good idea even though you can get it to work
- unistrut is expensive

So I've decided to mash together everything I've seen others doing in this same situation and came up with the following, which I think is pretty simple:
- build the frame out of 4x4 (vertical supports) and 2x6 (panel supports/cross members)
- anchor 4x4 vertical supports to concrete piers, with one north and one south support every 2 panels
- use iron ridge horizontal rails to mount the panels, in two rows of 18

No I did not hire an engineer to vet this design. I did some back of the napkin math for static load along with expected wind force and snow load (both pretty light in my area) and went above and beyond that (as far as I can tell anyway). I will be treating the heck out of the wood and reapplying every couple years to make sure it lasts as long as possible.

Anyone see any glaring issues with this? here are some pictures from sketchup with dimensions shown.

 

[TomC4306]

4x4 legs. 2x8 beams. 2x4 ripped at an angle and attached to the 2x8 to stiffen it and provide a mounting surface for unistrut. Unistrut cone nuts, quarter inch by 2 1/2 in stainless bolts and washers.

 

[TomC4306]

9 x 235 pointed at 155⁰, 9 x 255 pointed at 205⁰. 39⁰ tilt (matching my latitude)

 

[karamazov]

@TomC4306 nice, thanks for posting pics! That's a heck of a grade you had to deal with there. I'm curious about a few things I noticed with your design:
- any reason why 2x8 instead of 2x6 other than strength?
- why split the panels up pointing SSW/SSE instead of all of them just pointing due south?
- why set your tilt to your latitude? currently I have mine set to a rough average based on the entire year, came out to 26 degrees for me

Still new to all this so I apologize for any dumb questions in advance.

 

[TomC4306]

My first two arrays were slapped together only two strings each and I learned a couple of things.
It was taking about an hour and a half after sunrise for the sun to come around and shine on the panels and the same problem in late afternoon. I would lose the Sun before sunset. By breaking the arrays I sacrifice absolute peak power but I improve my morning and afternoon production. Another thing I learned was that weather here is either clear in the morning and cloudy in the afternoon or vice versa and I wanted to optimize my opportunity to harvest.

The price difference between 2x6s and 2x8s was only two or three dollars and I wanted to over build a bit so that I can upgrade the panels at a later date without having to rebuild the underlying structure and 2x8s are a little bit stiffer than 2x6s for the span.
At 39° North latitude the sun is at 90° to the face of the panels twice a year, spring equinox and fall equinox. So that diminishes summer and winter but optimizes spring and Autumn. I'm getting ready to add a third array that is more optimized for winter production and thus will be tilted more steeply.

 

[Northernchateau]

My panels like TOMC4306's are all mounted on Kindorf / Unistrut to keep each array lined up then the bottom of the panels on fastened onto 2" EMT tubing so I can rotate them and change the angle as I need to.
All that is fastened to a pressure treated frame work which is screwed down to my garage roof or side.

 

[chilly2]

Nice! How has it held up since? Snow, wind, etc.

I wanted to try unistrut and clamps (as my panels don't have frame holes for bolts) but was worried the clamps one sees on Amazon will be the wrong size to slot into the unistrut, so I have two questions for you!

- It looks like you have used clamps, but I can't quite tell. What did you use? Do you have the part number / source?
- If that is unistrut, what exact size is it (and can one get it at Home Depot / Lowes?)

 

[42OhmsPA]

Nice! How has it held up since? Snow, wind, etc.

I wanted to try unistrut and clamps (as my panels don't have frame holes for bolts) but was worried the clamps one sees on Amazon will be the wrong size to slot into the unistrut,

They are.

so I have two questions for you!

- It looks like you have used clamps, but I can't quite tell. What did you use? Do you have the part number / source?
- If that is unistrut, what exact size is it (and can one get it at Home Depot / Lowes?)

Here's what I used.
Post in thread 'Mounting panels with unistrut' https://diysolarforum.com/threads/mounting-panels-with-unistrut.10109/post-889667

 

[TomC4306]

Nice! How has it held up since? Snow, wind, etc.

I wanted to try unistrut and clamps (as my panels don't have frame holes for bolts) but was worried the clamps one sees on Amazon will be the wrong size to slot into the unistrut, so I have two questions for you!

- It looks like you have used clamps, but I can't quite tell. What did you use? Do you have the part number / source?
- If that is unistrut, what exact size is it (and can one get it at Home Depot / Lowes?)

Over two years, no issue.
I used stainless ¼x2½ bolts/washers and the strut channel nuts. The outer bolts need a spacer. Use ¾ EMT.