tytower

I gave up smilies in Kindergarten

Anyone who would make a solar collector out in the sun would be a dope wouldn't they?

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I Hate Microsoft-the site below says it well
http://www.vanwensveen.nl/rants/micr...eMS_intro.html

Sig239

Well I'm glad you can count to 11 without removing a shoe now, but on forums the smilies/emoticons are used to convey the context of what someone is typing.

I'm sure someone as brilliant as you has never made a stupid mistake! See, just not quite the same without the emoticon is it?

Marks256

lol, Sig239 told you, tytower! (oops, that is right, you are in first grade, and are too good for the smileys...)




hell, one more for the road...

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phantomroller

HarveyH42

I read your post and the replies with some interest; I have a 10 footer I plan to get around to playing with at some point in the future. A few points…

1. Mylar is very reflective, but bubble wrap is terrible for focusing as the bumps (bubbles) will scatter the light all over. If this is just a short term experiment grab a couple rolls of aluminum foil at the grocer and a can of spray adhesive, works great but will develop an oxide layer very soon when exposed to weather ( wont reflect well anymore). If you feel a need to use the bubble wrap (true recycling) I suggest you flatten it out before application, maybe borrow a lawn roller or use a baking roller etc to flatten (pop) the bubbles before application, the resultant surface will still be wrinkled and imperfect as a reflector but you will focus a lot more power. ( 3 M spray adhesive such as super 77 should attach the mylar very well)(Contact adhesive applied with a roller will work as well).
2. When attaching you will need to do so in sections roughly pie shaped with convex edges, the easiest way to explain what I mean is to take half an orange, cut it in eights, then peel the sections, the skin is not a perfect pie slice, the sides bow out slightly, being a half sphere (roughly) this is exaggerated to what you will face with you parabolic dish but you get the idea. The easiest way is to make a pattern out of clear (or semi clear) plastic such as visqueen, but since you have a mesh dish you can just work in the Mylar if you like. I would still deal in eighths, cut you sections generous in width, have a friend hold the pieces in place and mark the edges from the other side with a marker (sharpies work well).
3. Be careful, there will be a lot of power the focus pt. Keep this facing AWAY from the sun when working on it
4. Much has been said about the focus, but you probably want to be a little inside the focal distance (closer to the mirror). You will need a larger collector, but the temperatures will not be so extreme (though still plenty hot) so it will be easier to make a practical collector. I would guess that a 6 to 8 inch disk would be the smallest practical collector diameter. Yes, as has been mentioned this will cast a shadow on the dish, but if we assume the following The sun is a nearly infinite distance away therefore the suns rays will be coming in parallel to each other there fore the size of the shadow is the size of the collector so any energy lost on the mirror can be absorbed on the backside of the collector (paint both side flat black). I took some liberties, but from a practical standpoint working with homeowner tools, any variation from what I said is negligible. ( P.S. at the exact focal point you will have a hard time not just burning holes in your collector).
5. Be careful!!
6. Oh yeah, the collector, I would suggest a copper disk with copper tubing soldered to the back. You can get the materials from a hardware or home center ( if they don’t know they have the copper for the disk ask for a piece of copper flashing) (You could also try a metal recycling or scrap yard) the copper id a great conductor of heat and solders easily ( aluminum is a great conductor but hard to solder, unless your skilled I suggest copper) I would wind the tube in a flat coil, clean the metal surfaces both disk and tube, lay the coil on the disk, apply flux and heat ( camp stove, BBQ , torch, etc). Remember you want both the tube and the disk to be at the same temp and just a little hotter than hot enough to melt the solder. Once soldered kill the heat and let it cool, don’t wiggle it before it sets as this will create micro fractures in the solder that will mess up you heat conduction. In operation if your flow rate of water (or other working fluid) is great enough you should be able to keep the temperature of the collector below the melting point of the solder. There are plenty of possibilities for a collector but this is easy.
7. Be careful!!! The energy at or near the focus is considerable, but it does diminish rapidly at distance, at twice the focal length the intensity of the reflected light will be equal to ( or actually less than) the incoming light, so no death rays or beam weapons here.

OutToLunch

this has been done by the guy at cockeyed.com ...

http://www.cockeyed.com/incredible/s...h/dish01.shtml

HarveyH42

I did the mylar bubble wrap a year or so ago, wasn't too thrilled with the results. Think it was around 160 F. Been cleaning up the yard, and need to move the dishes. Kind of thinking about trying the 12 foot dish this time...