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Author Topic: Solar Trackers, DIY, How to.......  (Read 43734 times)
clockmanFR
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« on: March 01, 2012, 11:15:39 AM »

I have other strings on this forum running so i thought i could bring them into one Topic string Here.

    Positioning Solar Trackers? (Inventions, Ideas, Innovation, Bodges etc.).
    PV Panels For Solar Trackers, please?.  (Solar Photovoltaic Systems).
« Last Edit: March 01, 2012, 11:22:09 AM by clockmanFR » Logged

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clockmanFR
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« Reply #1 on: March 01, 2012, 11:38:43 AM »

sorry biff trying to reply to your post here, getting mixed up.

Quote from: biff on February 29, 2012, 09:11:45 PM
Strewth,!! Clockman,
                            I am still learning to walk again and digging is still beyond me,I would dig it in seconds with my little ex60 but you are much too far away and the council frown every time i use the tracks on the public road.It might take a day or so to drive it over to your place.
    I am glad to hear you got your panels.It sounds a fantastic price.
    I have figured out what is wrong with the 2kw prop and if the weather tomorrow is kindly i should be able to put it right in 15mins and send the baby up again
.It has been a while since she and i have had a holiday and the last trip to marakesh was just ok(much too much poverty),So we might take to the road and journey through France again and you never know we could pay you a visit.
   Meanwhile i look forward to seeing some pics of your trackers.My own revised plan is a lot more simple,designed with wind survival in mind.
                                                                                                             Biff




Your allways welcome biff just finishing painting etc in the Gite, and for this year its free accommodation for folk who help us out. Do not worry no digging, but, do need help with a set of fiberglass blades i need to make with my moulds. Ps still got 50 bottles of good cider that requires using! 

This time of year the ground is fantastic to dig as it comes out in wedges on the spade, just right. In the summer it hardens and you need a pick axe.
I have 150 meters of trenches to do as well so might hire a little minidigger, but at 200e per day its expensive here.
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clockmanFR
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« Reply #2 on: March 02, 2012, 08:14:01 PM »

Okay, I have worked out the basic design and on collection of the actuall steel stock next week (Monday 5th March) i will put together the drawings. (If they don't have the steel stock in, i will have to take a different size and redesign accordingly).

The base mount and main 3.5m pole design is okay,
The main Panel frame is okay.
The East to West hinge mount system is okay.
The seasonal declination adjustment is okay.
Tracker circuit and actuator arm are okay.
PV Panels 8 for each tracker, are okay, but fastening the PV panels down is NOT.

There are 4 rails on the tracker frame that the panels will fasten onto.  These 4 rails are steel 4.2m long and 30mm by 50mm and 4mm wall, and an integral part of the structure, but i do not want to put holes in them or weld clips on to them, as they would be weakened. 
I had though about U bolts and ally clamp, but U bolts are never really successful at holding on a square box section.

The solution at present is to use Ally angle 40mm by 40mm by 4mm thick that has one side vertical along side the PV frame and secured to it with 2 self tappers, and the angle that sits on the steel box extends beyond the 30mm width and has 8mm bolts either side of the box and a plate underneath the box. Its easy to make but just allot of work and allot of bits, ie, 4 clamps per frame soon adds up. It wouldn't take long to make a jig etc but its just extra work.  I have allowed the 40mm between frames for clamps on the rails and hence the rails at present are 4.2m long.

ANYONE out there got a clamping solution that's easier and cheaper?Huh??      genuflect
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rogeriko
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« Reply #3 on: March 02, 2012, 08:39:13 PM »

Just use regular roof mounting rails and hardware, bound to be an easy way to fix them to the steel box section.
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DaveSnafu
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« Reply #4 on: March 02, 2012, 08:40:48 PM »

why not build frame from Unistrut ? no welding all bolts, lots of fastening options.
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stannn
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« Reply #5 on: March 02, 2012, 09:18:16 PM »

Hi Clockman
Without a sketch I am not certain that I fully understand your bracket proposal. However, I do not like self tappers in this fatigue loaded structure, especially in aluminium alloy.
Stan
« Last Edit: March 02, 2012, 09:38:11 PM by stannn » Logged

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« Reply #6 on: March 04, 2012, 10:06:02 AM »

Davesnafu, and rogeriko,

The ally standard roof mounting rails are not much use with my structure as i said the rails are integral in the structure and will take loading and twisting form the wind. Just clamping the ally roof rails to the steel structure unfortunately will not cut the mustard.

I saw these pics of std rails used in Trackers and the way they had twisted and thought.....  Cry

http://www.fieldlines.com/index.php/topic,145734.75.html?PHPSESSID=e1e0735a2dd24c61622906ec79a7611e

stann, here's a quick sketch on back of envelope job. As long as the angle brackets butt up tight to the PV panel on the 4 brackets per panel, then the self tappers are just locating points.
 


* P3040101b.JPG (78.53 KB, 323x430 - viewed 2050 times.)
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clockmanFR
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« Reply #7 on: March 04, 2012, 10:15:56 AM »

biff, Nice day yesterday, saturday, 2 holes 2m/2 dug just another 5 to go.

As regards wind problems have a look at this thread on US forum Fieldlines, and at the end of the thread is a craker of a tracker, just the thing for the BIG boy's, desperate is this what you thought about?.

http://www.fieldlines.com/index.php/topic,145508.25.html?PHPSESSID=e1e0735a2dd24c61622906ec79a7611e
« Last Edit: March 04, 2012, 10:29:14 AM by clockmanFR » Logged

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stannn
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« Reply #8 on: March 04, 2012, 10:17:32 AM »

Hi Clockman
Yes, hollow sections such as RHS or round tube are the order of 100 times stiffer in torsion than are equivalent-sized open sections such as angle, channel or I-section. I would use aluminium-alloy rivets any day in preference to self-tappers between PV frame and bracket. They can be drilled out if it's ever necessary.
4mm thick looks lightweight for those ally angles, which you will be trying to bend when you tighten up the clamp bolts. I think that 6mm thick would be more appropriate, with the bolts as near as poss to the sides of the RHS. The lower bracket ought to be angle section too rather than flat plate.
Stan
« Last Edit: March 04, 2012, 10:31:58 AM by stannn » Logged

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« Reply #9 on: March 04, 2012, 11:24:07 AM »

Morning clockman,
               You asked about clamps.May i suggest you get your hands on some 50mm scaffold pole fittings,brackets and swivels..Split the swivels by removing the swivel pin(drill it out), If you sit down with these for a while you will see that there is lots of different ways you can use these,,especially when you discover that they can clamp 50mm box just as well.
   Buy new fittings,they are quite cheap and are really strong.
                                                           Biff
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clockmanFR
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« Reply #10 on: March 04, 2012, 01:11:54 PM »

Good afternoon biff, firstly good luck with that heat and hammer.
Regards scaffold clips, yes i see your concepts, and yes they are stupidly cheap, and i have sacks of them for my scaffolding.
But i am trying to keep the distance between panels as small as possible and at present the angle bracket works out at 40mm plus the thickness of the angle itself when the brackets are double stacked.

stann, Thanks for your comments and the riveting system is noted, although i have never been enthusiastic about pop rivets. (brings back memories of the late 1970's car body repairs argh!). so might fit 4mm bolts with nylon lock nuts.

Yes i had intended keeping the clamp bolts as close as possible to the box section, probably allow 0.5mm to 1mm clearance. As regards the thickness of the ally angles, yes i would prefer 6mm, but then thinner would bend slightly to get a good seat, and 12  of them would be double stacked as they are between frames. And i certainly do not want to bend or deform the steel box section. Regards the bottom plate, i had allowed for it to bend slightly. But on reflection 40mm x 40mm x 6mm angle would be better.   

Its a fine line between minimal materials that does the job, safety margins, and going Agricultural with massive over engineering that triggers/cascades those extra materials into the finished design.. 


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DaveSnafu
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« Reply #11 on: March 04, 2012, 04:14:31 PM »

The unistrut I use is 41mmx41mm, galvanised 3m lengths, you use the zebidee nuts that go in the channel, drop bolt through existing mounting holes in panels and tighten, job done, if you can bend a length of galv unistrut then you are a stronger man than me.
Its also really cheap and can be found in scrap yards.
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stannn
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« Reply #12 on: March 04, 2012, 05:04:09 PM »

Here's the coffee-time challenge to show the vastly superior torsional stiffness (not bending stiffness) of a closed structural section (like RHS) over an open section (like a channel). Take a toilet-roll core in both hands and try to twist it; it's pretty stiff huh! Now, with scissors, cut the tube once along its length and try twisting again. The torsional stiffness has all but disappeared! That's because it is now an open section. Notice that, when twisting, the 2 cut edges slide parallel but opposite ways to each other. That is because the shear forces on each side of the cut (caused by torsion) no longer have a path to react each other.
It's exactly the same with metal structures, etc.
Stan
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« Reply #13 on: March 05, 2012, 08:56:39 PM »

which is why unistrut has returns on each plane to increase torsional rigidity, check it out, its dirt cheap, it is grown up mechano.
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« Reply #14 on: March 05, 2012, 09:29:54 PM »

DaveSnafu
Those returns on the 2 free edges of unistrut are there to increase the buckling strength of the section when those edges are in compression, as occurs when the section is carrying a bending load or is carrying an axial compressive load. You can imagine that, without those returns, the free edges would buckle into a series of waves.
Unistrut is an open section (for obvious reasons) and filling in the missing face to create a closed section would make it perhaps 100 times stiffer in torsion. It may be harder to see this than in my toilet-roll experiment but a much higher torque on the steel section would show that this is true.
Stan
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