Possibly the Perfect Reflective Surface for Solar?

Tho here's a tip; make sure the grain of the aluminium is running across, ie horizontally to the curvature. Vertically for some reason badly affects the optics.

Had to learn that the hard way.

I see a "grain" in bought aluminium sheet too. If you shine a laser pointer on the material, you will a strange scattering of the light. I think the grain is bad news. Maybe a little polishing will greatly improve your results?

Just buy the correct reflective material and be done with it - no big deal.

Seems like flogging a dead horse.

There is a price performance scale, so there is no correct material. It goes all the way from kitchen foil price to space aged price. And everything degrades over time. He is trying to do this as cheaply and robustly as possible.

I know that he is trying to do it cheaply - why not use someone else's experience?

Good material as George used in the link is not at all expensive.

Looks like the stuff he's ended up using is about 8-10 times the price of the aluminium, if you can find it. Seems like good stuff, but these sheets should be about as reflective and easier to source. Might require a polish...

Just a note that I suggested showing the effects of polishing with a laser pointer to Ed (who owns the solar projects group at yahoo groups). I cannot remember which aluminium surface he polished but the effect was remarkable! It might just have been a buffing. The "grain" in aluminium has a terrible effect on reflected light. I just came across this thread again by accident. He has a before and after picture of the pointer light bouncing off the material. http://groups.yahoo.com/group/solarprojects/photos/album/1550335105/pic/list You might have to join to see the pics. Anyway, it is the reflected "point" before and after polishing the aluminium.

Brian

Very interesting.

It looks like the reflection is only being blown out in the direction of the grain, so in the case of a parabolic trough as long as you have the curve running across the grain it shouldn't make too much of a difference.

Buffing/polishing is an option, but if it can be avoided then it's one less thing to do.

I don't remember for sure, but I think that if a strip of material sags a bit, and you simply push the edges closer together, you get a parabolic trough. If so, this would work for a hardware cloth backing with a layer of foil in front, or for a somewhat thicker sheet of reflective material without backing. On that basis, mass manufacture would be easy. Then use a suitable ratio "clock drive" for tracking. This seems to be what you have done already, which looks quite good. Best of luck in advancing this concept.

Re: I don't remember for sure, but I think that if a strip of material sags a bit, and you simply push the edges closer together, you get a parabolic trough.

I guess a purist would tell you it's a catenary, but there is so little difference I don't think it matters--see the graph on this page: Catenary and Parabola Comparison - Math Forum - Ask Dr. Math

It's also interesting (to me ;-) to note that while an overhead transmission line is a catenary, the cables on a suspension bridge with a suspended flat roadway beneath it is more nearly (but apparently not quite) a parabola. A suspension bridge like a footbridge where the walkway follows the curve of the cables is a catenary. I found these in the Wikipedia articles on catenary and parabola.

I'm not sure, but I thought it was actually a parabola rather than a catenary. This is deflection/bending rather than tension/hanging by an "infinitely" flexible member. Your link sounds interesting; I haven't checked it out it but will go there next. Whichever way it turns out, it should still work as a solar reflector.

The weight of a catenary is spread evenly along its arc length; the weight of a suspension bridge is distributed nearly horizontally.

Re: deflection/bending rather than tension/hanging by an "infinitely" flexible member

I didn't think of it as deflection/bending rather than tension/hanging, so you may be right--I'm probably way out of my league. I just know that overhead transmission lines are catenaries, and assumed (I know) that this was a similar situation.

Just for curiosity sake, someday I'd like to know for sure, but I won't lose any sleep over it. ;-)

I managed to get a catenary into my cad package and compare it to a parabola. Basically what I took away is that if your curve is cut level with it's own focus, ie where it's 45 degrees, the difference between the two is pretty much within optical tolerances.

However, after that the caenary starts to deviate and after two or three times the focus depth is pretty far off.

Might be a catenary, which is superficially similar , but not the same as a parabola.

Look at what this guy has done - neat and well laid out.

Materials sourced etc.

http://georgesworkshop.blogspot.com/

What about Fresnel lenses made of broken bottles ;-)

I have read your comments concerning these aliminum plates but how would you use them, you know set them up? How many do you need overall, to say, run a household? I'm rather quite curious? Maybe to curious for my own good some people say?