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Need anodized aluminium flashing for solar concentrator

March 31, 2009

Hello,
I have been searching for a viable way to make a solar concentrator (parabolic dish) for cooking meals , heat water and such with the sun.
I guess the best reflective material (the main concern being shape preserving and best reflectivity) for this pourpose would be aluminium flashing as I have seen it is used here:
www.backyardnature.net/j/solardsh.htm
Now I wonder if it is possible to find anodized aluminium flashing at a reasonable price ( I haven't been able to find it on Google).
I need 'anodized' aluminium because I read that is the only way to have it last longer (5-7 yrs).
Thanks

Gabriele Betti
- Florence, Italy

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Hi, Gab. Millions of anodized aluminum reflectors are in use on street lights, indirect lighting fixtures, and doctors & dentists lights -- so it's probably the appropriate material. The issue is that, unlike aluminum which is relatively soft, anodizing is a very hard and brittle material. I don't think you'll find rolls of anodized aluminum; rather it is usually anodized after fabrication. That may be cost prohibitive for you. That article you reference is great.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
March 31, 2009

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April 2, 2009

Hello,
thanks for appreciation .
If you are interested in the subject here is a link to a serious source of informations of developing such items (solar cookers):
home.arcor.de/ernst.willand/amsi-contents.html
This are plans for rural areas development of solar cooker:
home.arcor.de/ernst.willand/amsi2.pdf
I am waiting for an answer from a local supplier of anodized aluminium , we'll see..

Gabriele Betti
- Florence, Italy

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Hi,

Ted is correct in his comments. However, aluminium is electropolished and anodized in sheet form and coiled. For the reasons that he states, it is only suitable for use in flat reflectors or those with simple curves.
It is important to understand that the reflective properties of anodized aluminium are very different a visible light wavelengths and at infrared. Light passes readily in the visible range but at IR is absorbed. If I remember correctly peak absorption is at ~ 3 microns wavelength. For this reason reflectors for heating should be limited to less than 1 micron thickness of anodic film. In the visible range this results in significant iridescence. The corrosion resistance would only be slightly improved over unanodized aluminium for outdoor applications. Also polishing does not bring the same improvement at IR than it does at visible.

The moral is: if you are mainly interested in IR don't assume that you can use visible light data.

Harry Parkes
- Birmingham, UK
April 2, 2009

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It appears that some recent inquiries about bright dipping and electropolishing of aluminum have hit one of Mr. Parkes' sweet spots. Thanks, Harry, for the very knowledgeable responses!

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
April , 2009