Solar Tracking for Solar Cookers and Solar Panels, Project Update

Nice project.

It isn't a tiny imperfection, here in Canada, the entire surface of foil has little corrugations on it. Its like the roof of a mini shed all across the bright side of aluminum foil. I got so much pushback from the solar cooking guys, (who absolutely refused to point a laser pointer at pieces of various different materials), like chocolate bar wrappers, or metalized chip/crisp bags or tinfoil or aluminum roofing sheet, I couldn't believe it! I just thought "these guys are being weird, whatever happened to experimental evidence and repeating experiments to prove right or wrong?". And I also found them to be acting like a cult. My tests clearly show that foil and alu sheet has vastly different reflections in different directions, which might mean that if they apply the foil in a different direction, they will get more heat. But they simply "don't want to know". I just find that incredible. The only people using foil are people doing youtube videos, and people in refugee camps. I think both sets of people should be told the truth, especially the poorest of the poor. The other weird thing is that for the commercial solar cooker that they (solar cooker group leaders) use in videos, no foil is in evidence, its all polished anodized aluminum, and metalized tape from China! As far as I can see, they are a cult, AND a bunch of hypocrites. So I took out my microscope and looked at the surface, and then shone lights and sunlight on foil and rotated it. Same effect as the laser pointer. I Then I found this research from India. Comparison testing different materials These guys in india didn't try foil because it was too hard to put on. They used Foil tape instead. They were testing specifically with a parabolic dish. https://www.jetir.org/papers/JETIR1905A27.pdf I will use a tighter curve than a parabolic dish when I get round to it, but the lost heat from aluminum foil's erratic reflection will still be very significant. I am still mad that they refuse to test different materials at solar cookers dot org. They do comparisons of different "commercial" solar cookers but amateur designers like me don't know which materials give the best results so we are at a huge disadvantage. Based on the Indian tests, vinyl car wrap is a good material, and I will probably buy it. But I don't know what brand to use. A swiss guy used some German tape to do his parabolic dish, so I might go with his recommendation. It's just hard to get stuff direct from a German factory here. Anyway, another issue with foil is that it whitens, (oxidises) very easily. Polishing and adonizing are non starters for normal aluminum sheet too. Adonizing just thickens the oxide layer so if it has grooves in it at start, it will still have them when the oxide skin is thicker. And polishing doesn't work because the oxide layer is Aluminum oxide (polishing grit). Members were not forthcoming about the reflectors on their fancy solar cookers either. They kept mum about the materials used. But anyway, here's the deal, if you can't see your reflection in it, it is a bad reflector for covering parabolic dishes. Pure and simple.

The corrugations are due to the manufacturing process & are from the rollers used to move the sheet through the system.

Mirror polish aluminium sheet is commercially available ie here. In the UK, there are companies that small sheets at around 300mm square for about £5 or they will cut to size. You should be able to find someone local who does the same.

I looked at some kitchen aluminum foil and it's not as reflective as I remembered.

Here is something that looks promising:

https://vivosun.com/VIVOSUN_Horticulture_Reflective_Mylar_Film_Roll-p58820960379606002

You have the problem of converting the flat film to a paraboloid of revolution reflector. The best way I can think of is to cut out long thin triangles, for example, 36 triangles with a 10 degree angle at the pointy end. With all the pointy ends meeting at the center, the triangles could be supported by a parabola shaped support. Just a thought, you may have a better idea.

Hope this helps...

Thank you, yes, foil may have changed over time. I don't remember it being terrible 15 years ago when I did my original experiments. (The worldwide solar cooking community refused point blank to point laser pointers at any reflective materials to check if my results held out everywhere). I do "cone solar" where I make sections of cones out of chloroplast to approximate the parabolic dish shape. This means I (hopefully) won't have too much of an issue sticking reflective material to the backing. (Plus it doesn't come to a sharp focus like you mentioned) so less likely to burn food or nearby objects or burn or blind people. A solar cooking researcher from Norway originally told me about the cone solar idea. Before that I was only aware of the "petal" method for making solar dishes. I can't upload my pic so its text only for now.

How big is the reflector? Could you get a parabola 3D printed & use that to form the reflector?

I have already made the reflector, but haven't added the reflective material yet. Originally I was going to use foil, but then I realized it won't work well in a parabolic dish. And it has to work well or everyone will conclude that my dish is rubbish. I'll try to edit my original post to put in pictures of the dish and its "tighter than parabolic" shape.

I've designed many reflectors in the past (long ago), parabolic, elliptical & other shapes, in my days as a commercial lighting designer. Used to use silver anodised aluminium from Anacoil, either polished or stippled depending on the requirement.