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Fresnel Lenses

 
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I would appreciate anyone's experience with them , & how you have used them ! I am trying to figure out how I can apply them on my homestead ! Thanks in advance for sharing ?
 
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I have used them as a cover for copper coil pipe that I'm using for solar hot water. Focuses it, makes it a bit hotter. In the New Mexico sun, it can make it too hot, if you are not using copper, be careful! I have heard of plastic pipes melting! I had it focused at the intake point, to get the heat highest there fastest.

I suspect it would help in solar cooking, although I haven't tested it, not necessary in NM, and not having a cooker running in MO yet. Want to test them on a solar dehydrator too.

I currently have one off a projection TV (about 3 foot by 4 foot) and I have a stack of the little ones that you can get at the dollar stores as page magnifiers. I want to try them in a frame, making a multipaneled fresnel array, probably for dehydrator. For what it's worth, I have had a harder time finding the little 8.5 x 11 inch ones lately, don't know if they are going out of style or what. My mom called me from out of town "this dollar store has them, how many do you want?" I told her to take all they had, she brought home about 30 of them. If they work I don't want to say "I want more and can't find any!" I also check every dead tv I go by, to see if they have a fresnel screen. Haven't found any yet, but I keep looking! The one I have I paid 10.00 for, a tv repair shop that the guy said "I wondered if anyone would buy them!" Why yes, yes I would. He has my phone # in case he finds more.

If anyone is wondering why they are interesting to the solar types, this is what a fresnel lens does, and if you flip it over, it takes diffuse light and focuses it.


These are the little ones like I get at the dollar stores:


And these are the type of tv that has a fresnel lens. If you look across the screen from the side you can see the ridges in the underside of the glass (plastic, but looks glass.)
 
pioneer
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I get those TVs free on Craigslist and take the lens out.  There are almost always a couple available.
 
Pearl Sutton
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Trace Oswald wrote:I get those TVs free on Craigslist and take the lens out.  There are almost always a couple available.



My problem with that is the rule is you have to take the whole tv, not just the lens. And I'm not strong enough to load, unload and deal with those puppies. They are HEAVY.
 
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There's a guy that attends a regional energy fair here that has one on a pivoting frame.  It will burn wood with sunlight in a couple seconds.  So it can focus a ton of sunlight on a pinpoint spot.  Or a hell of a lot just in front or behind that spot.

I think the biggest challenge is that it is at maximum efficiency if it's perfectly perpendicular to the sun.   So for a heating application I think you'd have to pivot it very often.  Unless you're just trying to boil a cup of water and then you could do it pretty fast.
 
Trace Oswald
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Mike Jay wrote:There's a guy that attends a regional energy fair here that has one on a pivoting frame.  It will burn wood with sunlight in a couple seconds.  So it can focus a ton of sunlight on a pinpoint spot.  Or a hell of a lot just in front or behind that spot.

I think the biggest challenge is that it is at maximum efficiency if it's perfectly perpendicular to the sun.   So for a heating application I think you'd have to pivot it very often.  Unless you're just trying to boil a cup of water and then you could do it pretty fast.



I haven't found a real use for it yet.  I'm not sure there really is one,  for the reason you said. I just play with it for the "holy shit" factor when you melt a pile of pennies or ignite wood almost instantly.
 
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Trace Oswald wrote:

Mike Jay wrote:There's a guy that attends a regional energy fair here that has one on a pivoting frame.  It will burn wood with sunlight in a couple seconds.  So it can focus a ton of sunlight on a pinpoint spot.  Or a hell of a lot just in front or behind that spot.

I think the biggest challenge is that it is at maximum efficiency if it's perfectly perpendicular to the sun.   So for a heating application I think you'd have to pivot it very often.  Unless you're just trying to boil a cup of water and then you could do it pretty fast.



I haven't found a real use for it yet.  I'm not sure there really is one,  for the reason you said. I just play with it for the "holy shit" factor when you melt a pile of pennies or ignite wood almost instantly.




There is an experimental solar in Arizona or New Mexico that uses these to focus sunlight on a Stirling engine to produce electricity.

There is a company in Michigan I think that produces Sterling Engines for $1800, but is only 1 HP. Still, it would be possible to get electricity from one.
 
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Green Power Science

This guy has been messing with solar death rays for years, along with other cool stuff.
 
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The fresnel lenses that consist of parallel ridges can be curved slightly to improve ambient and indirect light capture. It would also narrow the beam's focus.

I could see these, the letter-sized ones, arranged singly over solar cells to increase the amount of solar energy hitting them, gathered from static collectors that don't track the sun. The lenses would naturally be much larger than the cells, and some measure of cooling would be necessary to keep the cells within operational temperature range, but it would mean far fewer solar cells and hardware for better performance.

Conversely, they could be used in solar thermal power generation, where there is a half-cylinder reflector positioned with a boiler tube at its focal point. Fresnel lens panels could be used instead of clear glass to increase the amount of light gathered and then focused by the reflector onto the boiler pipe.

I was also thinking about their use, incorporated as panel arrays with the glazing in a greenhouse, where their focal points would each increase the amount of solar energy hitting black-coloured water barrels used for solar heat storage.

-CK
 
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This guy has been obsessed with Fresnel lenses for some time...
https://www.youtube.com/user/GREENPOWERSCIENCE/videos
 
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Greenpowerscience is where i saw it too. We have a bigun in a frame and the easel is almost complete. I use a store display shoe rack (for slat wall) mounted on a pedestal.

We kept a mirror from a smaller tv and use it to reflect sunlight upwards onto the bottom of the mug.

The rack is chromed wire and it lets the sun shine through it on the bottom of my large stainless mug, which is fire blackened from a decade of camping and backpacking. We have written cursive on sheets of plywood and destroyed a number of items for the science!

I snag them right out of the tvs but leave it neat. A phillips and a flat screwdriver will get you most of them in a minute or two.
 
William Bronson
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Right now I'm preoccupied with the idea of moving heat via steam.
I've figured 300 gallons of ground tempature water heated into steam, carries enough heat to keep my house warm for 24 hours.
If I could use  Fresnels to boil the water,  that would be great.
We would like to have sun tracking in order to maintain the focus.
But what if we could set up multiple Frensels to do the same thing?
What about a geodesic dome skinned in Frensel lenses that focus on a single spot in the center?
 
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I have one of the large tv fresnel lenses. It can burst a 2x4 into flames almost instantly. A project for this year ... hillbilly hot tub. Gravity fed into a holding tank in the garage. Small pump to refill the tub the next sunny day.
 
Pearl Sutton
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Chris Kott wrote:The fresnel lenses that consist of parallel ridges can be curved slightly to improve ambient and indirect light capture. It would also narrow the beam's focus.

I could see these, the letter-sized ones, arranged singly over solar cells to increase the amount of solar energy hitting them, gathered from static collectors that don't track the sun. The lenses would naturally be much larger than the cells, and some measure of cooling would be necessary to keep the cells within operational temperature range, but it would mean far fewer solar cells and hardware for better performance.

Conversely, they could be used in solar thermal power generation, where there is a half-cylinder reflector positioned with a boiler tube at its focal point. Fresnel lens panels could be used instead of clear glass to increase the amount of light gathered and then focused by the reflector onto the boiler pipe.

I was also thinking about their use, incorporated as panel arrays with the glazing in a greenhouse, where their focal points would each increase the amount of solar energy hitting black-coloured water barrels used for solar heat storage.

-CK


The reason I got all  those little ones was to try them in frames and make multi-focused framed panels I could try in various places and see what I like most.

I think framed panels like that might make good privacy screens on windows that you want the heat in, but not clear view, like a bathroom or sauna room.
 
Mike Jay
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If the sun is a few degrees off of perpendicular does it still do a pretty good job?  Or is it all or nothing?  I like the geodesic dome idea as long as it still does something if the sun is 1 degree off.
 
Mike Barkley
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I forget the spec but they can be off a few degrees. You could see the tv's from 20-30 degrees off center. The sweet spot is the exact center though.

I don't think an entire geodesic dome would be necessary for the small lenses. I believe a slice of the dome is enough since the (more or less direct) sun won't reach all sides of a dome during the course of a day. Would be an interesting experiment.
 
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