A little math help for the Cromagnon please lol

Alrighty,

I’m in the next stages of upgrading my setup.

My panels are currently mounted to portable skids using Tamarack UNI-90 ground mounts. In the current configuration, I have 4 panels mounted to a skid, facing horizontally.

I just bought 20 more ZN Shine 370w panels for my project expansion. I intend to mount these a little different, using 2-3/8ths pipe and C-Channel.

Where I could use a little help is on my measurements to get the panels at a 35* angle which is optimal for my geographic location. I plan on mounting (2) panels vertically, for 8 total on a skid.

Admittedly, math was always my weakness lol. With my old skids I was able to mock up what I needed to and play with the measurements to get it right. With this new setup, I’d like to have my math right before I start tinkering away. Hopefully the diagram makes some sense.

Thank you for supporting your local Marine/Cromagnon lol

So if I understand your question, you want to know how to pre-determine the front/back pole heights so that your new panels will be at 35deg. To do that, you need to know the horizontal distance between the front and rear vertical pipes. With that info, it's simple trigonometry. The "extra" height of the back poles divided by the horizontal length between the front and back poles needs to equal the tan(35), which is 0.7002. Or to solve it, 0.7002 x (length between front and back poles) = extra height. Doesn't matter how high off the ground the front pole is, as long as the back pole is that calculated extra height taller than the front pole, your panels will be at 35deg. Of course this all assumes that the T's, brackets and other mountings you put on will be of equal height on the front and back, which usually is the case.

BTW, nice job on your current mount. Not sure how windy your site is, but adding a few diagonal brace pipes from the top of one pipe to the base of an adjacent one, would greatly strengthen the mounts. The diagonal pipe can be much smaller pipe, and they can be attached in various way (fencing clamps do work and don't require drilling). A couple of diagonals (one in each direction) at each end can help quite a bit in wind storms. May not need it where you are, but cheap insurance if you do...

Steve777 said:

So if I understand your question, you want to know how to pre-determine the front/back pole heights so that your new panels will be at 35deg. To do that, you need to know the horizontal distance between the front and rear vertical pipes. With that info, it's simple trigonometry. The "extra" height of the back poles divided by the horizontal length between the front and back poles needs to equal the tan(35), which is 0.7002. Or to solve it, 0.7002 x (length between front and back poles) = extra height. Doesn't matter how high off the ground the front pole is, as long as the back pole is that calculated extra height taller than the front pole, your panels will be at 35deg. Of course this all assumes that the T's, brackets and other mountings you put on will be of equal height on the front and back, which usually is the case.

BTW, nice job on your current mount. Not sure how windy your site is, but adding a few diagonal brace pipes from the top of one pipe to the base of an adjacent one, would greatly strengthen the mounts. The diagonal pipe can be much smaller pipe, and they can be attached in various way (fencing clamps do work and don't require drilling). A couple of diagonals (one in each direction) at each end can help quite a bit in wind storms. May not need it where you are, but cheap insurance if you do...

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Thanks for the input!!

It gets EXTREMELY windy here. The skids I just built didn’t have an issue with around 60-70mph gusts. We generally have a N-NE wind direction, the goal is to have the front of the panels as low as possible to the skid. I also understand that putting 2 panels vertically now will increase my wind surface value considerably.

I’m working on determining the distance between the front and rear skid rails to determine how far apart they need to be to get my optimal angle. I guess that and the height for the poles is what I’m struggling with.

I know I can start setting it up, mapping it out and get it right but my way of doing things is definitely not the most efficient lol

If you have the room, you could put the panels up in landscape mode, 2 high. That would lower to total height, and front to back dimension of the mount/panels, but of course increase it's horizontal length.

If it's windy by you, I think some corner diagonals would be good insurance.

Steve777 said:

If you have the room, you could put the panels up in landscape mode, 2 high. That would lower to total height, and front to back dimension of the mount/panels, but of course increase it's horizontal length.

If it's windy by you, I think some corner diagonals would be good insurance.

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So that was the reasoning with going vertical vice horizontal. I have them horizontal now and they take up quite a bit of space. Adding more in a similar configuration would be possible, but not ideal.

I’m definitely open to some design ideas, I want to build this robust and I’m not concerned with spending a bit more to make it strong. I’ve also contemplated revising my current skids to this concept to handle more panels each.

I’m working on sourcing some 2-3/8ths Sch 40 pipe for the majority of this so it should be pretty strong, I also was looking at some H-Brace fittings to tie in the front and rear verticals.

I can cut, build and weld without issue, the “mathing” side of this project is where I’m lacking lol.

The 2 main front/rear joists will be 12’ long, with 1’ projected to hang over on each side. The spacing between the front and rear is what I’m working on trying to figure out.

I want to ensure the skid is wide enough to handle the winds while aiming for the 35* angle. Keeping the front edge lower also will help with the wind load.

Without going to full blown structural engineer (which of course is an option), the further apart your front and back row are, the stronger the mount will be. Of course you want both those rows to sit under the panels with some overhang. 1' to 2' overhang seems fairly typical, but there are likely other considerations for your situation.

In general, rectangles can rack under enough force. Imagine a hinge at each corner of a rectangle, you could push that rectangle so that it would be almost flat. Putting diagonal bracing in to form triangles prevents that (triangles cannot change shape, put hinges in their corners and you can't fold them). That is why adding diagonals strengthens structures, makes for triangles which don't fold. Without those triangle braces, you are relying the the "effective" triangles in your T's or weld to prevent racking, and that may or may not be enough.

While a part of the overall strength calc, the distance between the front and rear poles is not the only thing which goes into the equations. In theory the front and rear post could be 1' apart and it could be made to work, you would just have to greatly increase the strength/size of the other components to compensate (think of a pole mount, which it would be approaching). Not recommending that at all. Just saying it will be the whole system which ultimately determines its strength.

Probably have not given you the answers you are looking for. But wanted to raise the other "things" which need to be considered, like: how the panels will be secured (and grounded), uplift, racking (as mentioned), as well as wind loads.

The top of the upper panel is going to be 6'-6" above the bottom of the lower panel. That is a lot of area to the wind.

Also, with a portrait layout you need an extra row of structure-- your main horizontal pipe for your supports, something going vertical, and then the strut running horizontal. What do you see that intermediat support being made from?

If you are using Unistrut or similar then your maximum span is something on the order of 10' for the double height strut, but it is going to flex.

You can always use aircraft cable/guy wires with turnbuckles for cross bracing and a ground screw or two for uplift protection.

I appreciate the input and didn’t even think about using cable and turnbuckles as guy wires!

I planned for front and rear vertical stanchions off the base with (3) sets going vertically.

I then planned for 3 horizontal stanchions, all 3 being tied into the verticals at the ends.

They offer the strut in 10ft or 20ft sections, I’m now trying to calculate if I can do it with the 10ft or, if I need to go with the 20ft and cut to the (2) panel length. I think the 10ft may work.

I’ve also been looking into H-Brace cross bars to help strengthen it up. My current skids are set up with 2 panels, horizontally and they’ve done very well with the winds here. Obviously putting 2 panels vertically will change things quite a bit. I wish I was better at drawing my ideas lol

This is my first skid project designing the mounts as well so I appreciate the feedback for sure!

ChrisSwolls said:

I think the 10ft may work.

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Your strut is going to need to be at least 165" long to support all panels. I think you are going to want a pipe connecting the high-side supports together and another for the low-side supports; it makes it a lot easier to level things out.