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Old 09-01-11, 05:18 AM   #11
Paloma
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Which collector is good to use for home and cheap able also whether flat plate and evacuated tube collector. I need for all home equipments to save electricity problem.

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Old 08-17-12, 02:30 PM   #12
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Default brazing copper tubing to aluminum sheet

Hi all, I was just reading the thread blahname started on brazing copper tubing to aluminum sheet. I'm planning a DIY solar pergola project and am going to do my own flat plate collectors and integrate them into the pergola joist cavities. I've been to the local recyclers and have pricing on copper vs. aluminum for the absorber sheet. Its about 3 times the price and the sizes of their sheet will make it painful to work with. I'm also hearing a lot of problems with brazing copper to aluminum

Any advice on the tradeoff between cheaper aluminum and brazing challenges ?

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Old 08-17-12, 09:34 PM   #13
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Jeremy,

I did some testing on brazing copper to aluminum.

Step 1: braze something to the aluminum that can also stick to copper - something with a lot of silver in it.

I found I could buy two brazing rods for aluminum for $5 (retail), yes for only two and I did get it to melt in a pool atop bare aluminum then scratch under the molten pool with something stainless (like a brush) to get it to stick.

It stuck well, but the aluminum has to be quite thick to get it to work before you burn a hole in the aluminum sheet. I experimented with some bare flashing roll from a hardware store but wasn't pleased with the results.

Step 2: Braze same material to copper pipe

No problem, worked fine without issue.

My conclusion:

So this left me with the problem of either getting thicker aluminum and trying again, or going in another direction entirely.

I found that thicker aluminum was difficult to find and I really didn't like paying $5 for 2 brazing rods that might do 12" of copper pipe to aluminum sheet.

My chosen method is just plain 'ol silicone between the copper and aluminum.

Tip: If you'd like enhanced thermal conductivity from the silicone, you can add aluminum flakes or possibly aluminum oxide power to the silicone, mix well and apply somehow. I've not found a good way of making or getting any of that, so I'd likely not bother and make my solar collector a little larger and out of cheap materials instead.
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Old 08-18-12, 08:43 AM   #14
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Non-tracking reflector collector?
It seems like a well bonded flat aluminum/copper collector will have the edge,
until the sun is directly overhead.
Concentrating collectors work well in tracking arrays, but their 'gain' isn't
that great when the light is coming in from the side.


Redraw those lines coming in at a 45 deg angle. Much of that light isn't going
to bounce back to the water pipe.

Here's some tracker testing.
georgesworkshop: Index - Comparing concentrator to flat plate solar collector

I'm not sure if a stationary concentrator was tested.. Didn't read it all.

From my experience testing microwave antennas, I wouldn't use a 'gain' reflector, unless it could track the sun.
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Old 08-19-12, 07:43 PM   #15
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I have to agree on the reflecting collector not working at glancing sun angles. Trackers are a bit difficult, especially with moving parts and plumbing if you want to heat water, which is what I want to do. That and more moving parts = more points of failure. What would be nice would be a passive tracker that could rotate the reflectors inside a collector around the copper pipe, but the build complexity and cost goes far beyond the performance benefit over a flat plate collector in my view.

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