Solar

[bj]

    Hi all:

   It is 5 in the morning here, and as usual, I can't sleep.  Thoughts

going through my head--has anyone tried using an old satellite reflector

as a reflector for sun energy?  Most of the old ones (8 to 12 foot) are

I believe perfect paraballs(spelling).  This would mean, that if coated

with a morror like surface, they would focus the sun's heat on a focul

point.  Kind of the thing that some of us did as kids with a magnifing

glass.

    Anyway, my thoughts were, that if a 3 inch glass can burn paper,

what could a 8 to 12 foot dish do?  If time lets me, I may try with a

28 inch that I have, just to get a feel for the amount of heat.

   Will post results, but would welcome any comments,or experiences.

bj

[AbyssUnderground]

People would probably use smaller dishes for solar cookers. They work quite well when you have a full days sun. Wouldn't be much use in the UK though, the sun is pretty sporadic here.

[fcfcfc]

Hi:

I have a 3 meter dish that I use for high temp solar demos. The big thing is that most of the dishes are not smooth surfaced, but a "crinkle" finish and you have to sand them down if you wan to use a reflective film product. VERY TIME CONSUMING!! Great for demos but really for a regular source of heat, you have to be in clear sky country sense diffuse radiation is not captured. Tracking is not the easiest thing either, despite what you may see out on the internet.

[Volvo farmer]

Back thirty years ago, a class I was in cut 1" pieces of mirror and pasted them on a 6' or 8' fiberglass dish. It would instantly ignite a 2x4 placed in the focus.

Over at Redrok.com there's a short writeup about a guy who cast a copper coil in a hunk of aluminum with the intent of heating water or making steam with a large parabolic reflector. No real data on it though, as I remember.

[Bruce S]

bj;

   back in 2005 there was a flury of discussion about heliostats , which is similar to what you're looking into. Nando IIRC , had a good handle on the angles and tracking.

The quickest math for the focal point if F=d^2/x*16. F=focal point, d=diameter of parabloic, x=depth. Easiest why to find "x" is to get a tape measure , put two flat surfaces one on bottom one on top and measure.

This works on big ones and little 1 meter ones. The surface , if you're going to work with this can be covered with mylar or old chip bags, Al on the inside makes nice reflective surface. The Focal point can get hot enough to melt Aluminium so please becarful.

Also Redrok has a pretty good write up. Plus on here there are a couple people who are in fact doing this kind of stuff in Texas:-) hopefully they'll chime in as well.

Cheers

Bruce S

 

[PHinker]

   Redrok (www.redrok.com) has a number of writeups on this sort of thing.  If you're ambitious and handy, there's a very complete description of how to build a large concentrator here (http://www.ida.net/users/tetonsl/solar/solarhom.htm)

   Another interesting (and much more simple to build) concentrator which is built with plywood, small mirrors, and silicon caulk is here (http://www.eskimo.com/~billb/amateur/mirror.html)

   I don't have any affiliation with Redrok but have found the website to be an interesting diversion from time to time.

[Bruce S]

VF;

 what you said :-)Redrok's write up is good reading.

There's Nando, and a really smart guy on here down in Texas that was/is building that large heliostat.

Cheers

Bruce S

[kurt]

veewee77 i think his user name is, Doug polished a 9' spun aluminum dish and used it for a solar cooker.... there are pictures in his irc gallery...

[TomW]

I think Dougs stuff is archived over here on the IRC gallery.

http://www.anotherpower.com/gallery/dougs-place

Just because not everyone knows what the IRC or its gallery are.

TomW

[stop4stuff]

here ya go

http://www.fieldlines.com/story/2006/10/12/143057/35

[feral air]

The Mythbusters did the same thing in one of their death ray episodes.

[vawtman]

Hi Beej

I've got an 8ft dish that i'm planning to convert to a solar collector.Thinkin of a plan of attack yet though.Would be easier and maybe almost has efficient i think.

Have Fun and alot of times my r.e. thoughts help me sleep.

[Jeff]

>> Have Fun and alot of times my r.e. thoughts help me sleep.

Funny, my r.e. thoughts gave my ex nightmares!

Seriously though, parabols make excellent concentrators, and also can gives humans instantaneous (and very nasty) burns! Make sure you have a very good collector!

[hvirtane]

I made once a reflector of a 80 cm satellite antenna. Used to test for solar cooking.

For solar cooking satellite antennas are not the right things. The focus point is too far and the thing becomes quite dangerous for your eyes.

To tell about really dangerous things. We once tested a high quality 1,5 m diameter parabolic searchlight mirror made of glass. We could melt steel with it. You might imagine what would happen if you put your head in the focus.

- Hannu