Mounting panels with unistrut

[42OhmsPA]

I see it has adjustable tilt.

Yea, honestly I'll probably tilt it a little steeper and leave it be, it seemed like a great idea at the time.

Horizontal braces provide good compression against the wall, but little tensile strength. The anchor screws to some extent, but especially the toe nails through brackets. I've used brackets for a shelf and noticed they barely bite.

I'm not completely following?
Are you saying it's good, bad or could be better?
I still have to add bracing between the posts. The diagonals I added to the frame are at least 1.5" into the wood. For the joist hangers I ran screws to hold the wood instead of nails to make sure they bit well. I used 3.5" tapcons into the concrete wall. (I remember ripping an old deck apart and thinking how little the joist hangers did for strength, more for support)

 

[Hedges]

Well, the posts in concrete look sturdy.
I saw that joist hanger attached to brick wall, thought it could restrain against array tilting toward wall, but not pulling away.

You may only have wind. I'm in California so think about earthquakes, 1 g in any direction, oscillatory motion. So my 2" rigid pipe uprights have diagonals in X and Y.

 

[DrewLoker]

I used 5/16 stainless hex bolts sourced from eBay.

Thanks for the replies and suggestions.

Part of my challenge was that I "committed" to 3/8" at HomeDepot when I bought 3/8" cone nuts, bolts and lock washers. But, I assumed I would be able to find 3/8" square washers and/brackets. But, most are 5/16" or 1/4".

Should I just drop down to 5/16? (I got the wrong length of bolt anyway...need 2-1/2".)

 

[Brett V]

Thanks for the replies and suggestions.

Part of my challenge was that I "committed" to 3/8" at HomeDepot when I bought 3/8" cone nuts, bolts and lock washers. But, I assumed I would be able to find 3/8" square washers and/brackets. But, most are 5/16" or 1/4".

Should I just drop down to 5/16? (I got the wrong length of bolt anyway...need 2-1/2".)

Home Depot has a pretty liberal return policy.

 

[DrewLoker]

Home Depot has a pretty liberal return policy.

Right…but I live in the country, so, can’t just pop into HD…thus the shopping on Amazon to source things. But that is one area Amazon has not been competitive. I do have an Ace Hardware in the nearby town.

But the question is of support of 3/8” vs 5/16”. I had decided to go 3/8 for the small price increase, but better specs. But of the 2pm or so items in my AZ cart, most would have to be modified one way or another…drill out holes for 3/8”, replace flange nut, etc. If I drop to 5/16”, it does simplify the seelction.

EDIT: I stuck with 3/8…and found the square washers locally.

 

[justgary]

I used some scrounged heavy gauge hat channel. Very similar to unistrut, but it let me drill and through bolt the panels directly to the strut on the brim of the hat.

 

[ricardocello]

I designed and built my own Unistrut ground mounts, it was definitely a learning experience.
Cutting strut and 2" poles, cleaning, painting, etc. is a lot of manual work compared to buying a kit.
But they are built and installed, and working well.

I did do the mechanical engineering beam loading simulations, as I really want it to survive the 109 mph winds.
I'm not a PE however, so this design is not suitable for permitting.

My requirements:
All metal must be locally available, and fit in my pickup truck.
Thus, Home Depot, Lowes, and local metal shops only.
For Unistrut accessories, I ordered directly from Unistrut Buffalo, cheapest prices I could find.
I've got bifacial panels, so these are 5' off the ground.
And I want to be able to set the tilt angle easily by just swiveling the array 4 times a year.
The 2" gold galv pipe clamps holding the panels to the cross beam are rated 800 lbs each, and there are 8 of them.

I've attached my plans below, perhaps it can give others some ideas.

 

[Hedges]

Just two vertical pipes?
Wind could bend them. I'd add a second pipe to make inverted "V". My location has earthquakes, so 3rd pipe in a different direction.

Do you also have a strut to hold array at some fixed or adjustable tilt?

 

[ricardocello]

Just two vertical pipes?
Wind could bend them. I'd add a second pipe to make inverted "V". My location has earthquakes, so 3rd pipe in a different direction.

Do you also have a strut to hold array at some fixed or adjustable tilt?

The anchors/poles are rated 3000 lbs lateral in this soil, and pullout at 2500lbs.

I am installing a third anchor connected to the bottom of the array in the center to form a triangle for stability as you suggest,
with an adjustable channel to get any angle between 45 and 10 degrees. Not installed yet, maybe this weekend.

 

[Hedges]

The anchors/poles are rated 3000 lbs lateral in this soil, and pullout at 2500lbs.

"Lateral", but that says nothing about bending moment.
I don't think height of pole figures into your equation, but it must to determine if the upright will buckle at the base and fall over. How much bending strength must Archimedes' lever have?



Form a triangle with another pole. Assume all ends are pivots with no torsional resistance. Geometry will then let you calculate lateral force and pull-out force for a given wind force (which you can probably get from a table.)

 

[Hedges]

I am installing a third anchor connected to the bottom of the array in the center to form a triangle for stability as you suggest,

Third leg to a point off the line of the other two should eliminate the bending problem.
Transfers it to the horizontal, which always has that (but distributed force, supported multiple places.)

I've poured concrete in thin metal fenceposts to make them stronger. Now can't buckle, has to stretch the metal.

Kinks are often done deliberately to facilitate bending. Prevent that and it is a stiffer, stronger structure.

 

[Sanwizard]

How are the panels attached to the unistrut ? I had planned to make up a fitting using a short piece of 90 angle but there may be other methods.

There are large square washers at home depot near where they store the Unistrut. The spring nuts work great with the washers. Use bolts from the hardware isle that fit the washers(3/8 or 1/2).
Unistrut works great for ground mount or roof mount.

 

[Hedges]

If you use 1/2" threads anywhere, I find the spring nuts' thread deformed by crimp process to retain spring. You might get the bolt in, but it seizes and can't be removed.

I chased some with a tap. When possible I buy without the spring. Plastic cone or no retainer.

 

[ricardocello]

"Lateral", but that says nothing about bending moment.
I don't think height of pole figures into your equation, but it must to determine if the upright will buckle at the base and fall over. How much bending strength must Archimedes' lever have?

View attachment 171181

Form a triangle with another pole. Assume all ends are pivots with no torsional resistance. Geometry will then let you calculate lateral force and pull-out force for a given wind force (which you can probably get from a table.)

I ran a cantilever beam calculator quickly to see what the deflection on the vertical supports would be at 3000 lbs dynamic load from 108 mph wind (30 psf) with the panels tilted 90 degrees (worst case, mine actually won't go below 45). Deflection was 6.3" per 5' pole, which means they would snap. Max deflection should be L/180 or 0.3 inches.

So the third leg is really mandatory. I'll have to do a real simulation to see what it actually buys me.
Or I can add 45 degree supports.

 

[ricardocello]

There are large square washers at home depot near where they store the Unistrut. The spring nuts work great with the washers. Use bolts from the hardware isle that fit the washers(3/8 or 1/2).
Unistrut works great for ground mount or roof mount.

stainless 5/16 and 1/4 hardware holding 5’ unistrut on sides in portrait orientation bolted directly to panel mounting holes
tape and nylon washers and painted unistrut to avoid corrosion
unistrut crossbeams with 5 hole U bracket, spring nuts(hate them), 3/8 stainless 1” hardware with washers, use anti-seize on bolts

 

[Skypower]

Just avoid the jello jiggles. Short corner braces are useless as in the first picture. From highest corner to lowest point will get you rigidity as seen in the last two pictures. Even if you extend short pieces to do it, its worth it(last picture) It also won’t take as many braces to do it.

 

[Hedges]

How much resistance to uplift does your design have?

 

[Skypower]

How much resistance to uplift does your design have?

View attachment 171227

Gravity ?

 

[Skypower]

How much resistance to uplift does your design have?

View attachment 171227

It’s between the house and a newer fence so it’s well sheltered. It’s only got to last a few more years at this location then it’ll either be disassembled and go with or more likely given to a buddy to make it go away before the next owner gets it. Think of it as a way to get my feet wet in solar. We had heck of a wind storm last winter and went out to see how stable it was and it seemed like everything else was moving but that. If this was out in the open your damned right it would be anchored in the ground and probably an engineered mounted system. If this heavy low angle panel thing lifts at this location, it would have to be an F3+ tornado which we just don’t get here. But yeah, your eyes are good.

 

[DrewLoker]

For the end panels where there's only 1 edge and the square hold-down doesn't have 2 panels to hold 'flat', I used a strut near the edge but completely under the panels. Used a piece of semi flattened EMT conduit to provide a base for the square hold-down to lay flat and not tilt off the edge of the panel.
View attachment 161272

I am re-examining your solution. I came up with something from seeing your solution initially based on what I had on hand, but it is not acceptable. I cut 1/2" PVC pieces at 1.5". The problem is the 1/2" doesn't fit well as it doesn't sit flat inside of the plastic ring with nut, and each piece I cut varies a bit.

So, I need to come up with something else. I see what I missed the first time of your...something under the panel, on top the strut. But I don't have much extra bolt to put too much there. The 2.5" bolt is not long enough for much to go under another 2mm thick washer.

So, I am trying to think of another piece I could put between the top square washer and rail. Maybe 3/4" PVC?

Any other ideas from others for the End Mounts?

Thanks!!

 

[OffGridInTheCity]

I am re-examining your solution. I came up with something from seeing it initially based on what I had on hand, but it is not acceptable. I cut 1/2" PVC pieces at 1.5". The problem is the 1/2" doesn't fit well as it doesn't sit flat inside of the plastic ring with nut, and each piece I cut varies a bit.

So, I need to come up with something. I see what I missed the first time of your...something under the panel, on top the strut. But I don't have much extra bolt to put too much there. The 2.5" bolt is not long enough for much to go under another 2mm thick washer.

So, I am trying to think of another piece I could put between the top square washer and rail. Maybe 3/4" PVC?

Any other ideas from others for the End Mounts?

Thanks!!

I used metal EMT conduit, flattened into an oval. I used the square mounting pieces under (and over) the EMT.


In another array/area I used these adjustable edge mounts to hold the edge down against the unistrut - had to fiddle a bit to attach to the unistrut but they are adjustable so I could find a solid fit.

Solar Panel Mounting Brackets-Adj End Clamp fit 35mm to 50mm -Pack of 20 | eBay

They are clear mill finish.

www.ebay.com

 

[DrewLoker]

Thanks the additional info. I had missed that you used an extra square mounting piece...thought you had stated it was something else even though it looked like another square. Makes sense. What size bolt did you use? I bought a box of 2.5", but may just need to buy some 3" singles. I don't think 2.5" is going to go through another square and have enough threads to get through the nut. I did put a lock washer also above the top square. Those squares are THICK!!

 

[OffGridInTheCity]

Thanks the additional info. I had missed that you used an extra square mounting piece...thought you had stated it was something else even though it looked like another square. Makes sense. What size bolt did you use? I bought a box of 2.5", but may just need to buy some 3" singles. I don't think 2.5" is going to go through another square and have enough threads to get through the nut. I did put a lock washer also above the top square. Those squares are THICK!!

Yea - I had about 3 lengths of bolts. Don't remember the details but it's details like this that just drive me crazy sometimes

 

[DrewLoker]

Yea - I had about 3 lengths of bolts. Don't remember the details but it's details like this that just drive me crazy sometimes

If my panel is 1-3/8, how thick should thick should the spacer be?

 

[OffGridInTheCity]

If my panel is 1-3/8, how thick should thick should the spacer be?

The EMT tube - you cut so the top washer is 'roughly' flat - so the distance from the base to the edge of the panel. I used a hack saw and got it on the 2nd try.