Why are solar panel mounts aluminium?

[frackers]

Greetings all

Just awaiting the delivery of 6kw of panels that I'll be mounting on top of the (nearly) flat roof of the shed (barn) so I'm starting to think about mounts, especially being able to set a summer/winter inclination.

I was planning on making the basic tilt frames welded up from 1.5" square steel tube but all the commercial mounts seem to be extruded ali - is this just for convenience or is there some other factor such as heat expansion, differing materials etc coming into play here.

When the panels arrive I'll be able to see if their frames are pre-drilled (is that normal?) or require some special clip.

So far I think I'll have 3 rows (24 panels, each 1.65x1m) mounted on their side, so only requiring 2 rails, on the roof which is 14x6m. The back row I might stand vertically, not done the geometry to check on shading yet!!

I live in a high wind zone so I'd prefer the added strength of steel, I don't want to end up doing things twice due to missing some basic facts!!

Cheers

[phil b]

Hi Frackers,
In the states, we can get "Superstrut" that's channel steel with oval holes every 6 inches or so. There are bits that make them work like Legos. I used the superstrut for backing on my panels almost 2 years ago. It has yet to rust except where I welded 2 pieces together. That might work for you if you can get it at a good price.

This link was easy to grab. several big box stores stock it. http://www.homedepot.com/buy/superstrut-1-5-8-in-x-10-ft-12-gauge-metal-framing-channel-za12hs10pg.html#.UPStC3jRL3w

Here's a man using the superstrut from start to finish. It IS a long story, but also detailed.http://ecorenovator.org/forum/solar-power/2070-4kw-grid-tied-battery-backup-system.html

6 KW of solar power? That should power about anything. I see lots of batteries in your future. 

[dnix71]

Steel rusts. Solar panels have a rated life of 20 years or more, steel doesn't. Weight is also a factor when roof mounting. Aluminum is much lighter, and certain aluminum alloys are actually stronger than steel. Aluminum is much easier to machine than steel, too.

We used Superstrut to reinforce rollup bay doors at work against hurricanes, but it's heavy. A/C guys use it to hang split systems, it can handle the loads.

[birdhouse]

one point that has not been mentioned yet, is the potential steel to ALU connection.  dissimilar metals...  and the corrosion/oxidation/electrolysis.  whatever it's called, i know it isn't good. 

maybe incorporate some dense rubber chunks between the steel and ALU so they never actually touch.

i used some chunks of roofing between my panels and the welded steel frame.  but my frame fully encapsulates the panels front, back and sides, so the roofing is just a buffer.  without it the panels still couldn't come loose. 

a heavy coat of paint might even be enough. 

6Kw...  WOW  jealous big time!

adam

[Mary B]

Aluminum and galvanizing are okay together. If they weren't the galvanized mast holding my antenna would have eaten the aluminum mounting plate by now.

[Bluevitz-RS]

I don't know about where you are, but here in Ontario, Canada the panels have to be electrically bonded to the chassis on which they're mounted and grounded in case of lighting strike.

[SteveCH]

The frames are pre-drilled. The predrilled holes often don't work for me, so I drill new ones. It is quite easy to do with aluminum. Place a block of wood behind the frame member so you don't slip up and hit the panel when the drill bit breaks through.

[madlabs]

I'm just starting to build a rack for 4kW worth of panels and I am using steel. Steel will easily last 25 years if properly coated. I chose steel because I have all the tools to weld it and so on. And I have to assume it is cheaper as well. I spent 800 bux US on steel.

Jonathan

[tanner0441]

Hi

As said steel if treated/coated properly can last, but maintaining the coating can be a problem if they are difficult to access. The problems with electrolitic actions can be minimised  by bonding out the mountings with tinned brass terminals with copper brading between them. It also keeps the complete setup grounded..

I would go for aluminium with stainless fixings. I have 4 X 20W panels so not even looking at your capacity but I bought ally angle and made my own adjustable mounts, the frame on my panels were pre-drilled. When I put my panels up I was in a position to weld aluminium but after a bit of thought went for nuts and bolts so I could modify or update without having to buy another welder.

Brian

[frackers]

Well you've all given me something to think about!! Some of the ideas I'm following up so far are:

• How long a length of steel can be cheaply powder coated locally
• How long a length of steel can be hot dip galvanised locally
• Find out about bonding requirements here in New Zealand
• Visit some of the local manufacturers of steel framing (used to build houses!) to see if its appropriate
• Experiment with mounting clamps with butynol roof membrane isolation

[birdhouse]

not sure about new zealand, in the states, 20' is a standard steel length.  both the powder coating, and galving shops around here can easily do 20'.  i'm trying to remember the booth at the powder coating spot last time i was there.  i think it was almost 30' long.  IIRC. 

even a quality, oil based, self etching, red oxide primer (two coats), and a few coats of oil based high solids paint should give at least a decade of protection w/out any signs of rust.  i always brush this stuff, as it seems to last a lot longer than rattlecans.   

i guess it depends on if you time is more or less important than you wallet...   

adam

[madlabs]

I just got a quote for powder coating and I think that is the way I am going to go. The quote was around 350 bux US. Considering that it would cost me close to 100 bux just for paint and primer etc, that seems very reasonable.

Jonathan

[tanner0441]

Hi

The size constraint on Powder coating is normally the oven, or if it is sprayed or fluidized bed. I became involved in making frames for plastic plating vats and they had to be epoxy powder coated.

Brian

[ghurd]

Usually, standard practice is to use SS hardware, and a SS washer between the rack and frame.
That way nothing except SS is touching any iron or AL / ali.

Personally, I use SS for all the fasteners.  Bolts, washers, lock-washers, jamb nuts, and nylon lock nuts.

A couple $ differnce in hardware keeps the AL/ali frame from rotting out.
Just my thoughts and practices.
G-

[madlabs]

Frackers,

Finished the first of my steel racks. I did get it powder coated and it is fantastic, much better than paint and worth the price. I posted a pic here:

http://www.fieldlines.com/index.php/topic,147530.0.html

Jonathan

[frackers]

I decided in the end to use galvanised steel box so I have 320m of 40x40x2mm box to be cut, drilled and welded. The prototype frame has been built and the cutting list optimised to get a frame for 2 PV panels out of 3x 8m lengths. The prototype will be used on the RE system to keep the batteries topped up. The frames are adjustable from 19 to 56 degrees which is the 2 summer/winter positions for this latitude. The prototype was tested by 2 of us jumping up &down on it - no flex!! Will use all SS fixings from the panels to the main runners on the frames.

Still waiting to hear what deals I can get on inverters, should know that in the next few days and then all the paperwork can go in. Already got the nod from the grid supplier and a quote for what they will pay per kw-hr

Cheers