Large Fresnel lens
Large Fresnel lens
(OP)
Is it possible to build a Fresnel lense with an diameter of 50 - 60 metres, maybe assembled in a frame/patchwork style construction? Maybe somebody already did this - are there any references?
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RE: Large Fresnel lens
<nbucska@pcperipherals.com>
RE: Large Fresnel lens
What is the end purpose?
TTFN
RE: Large Fresnel lens
I agree it would be a statics nightmare if one would make this a monolithic structure. But if one uses a structure like those made by Sprung Instant Structures and replaces the stressed membrane between the load carrying profiles with an optical material?
RE: Large Fresnel lens
in a steel grid.
The problem is that you need to have many "Fresnel-prisms"
and each need separate tooling.
I think it would be cheaper and easier to use a large #
of large flat mirrors with separate positioning systems
<nbucska@pcperipherals.com>
RE: Large Fresnel lens
RE: Large Fresnel lens
need thousands of pieces. Do you have any idea, how
many different ones you would need ?
<nbucska@pcperipherals.com>
RE: Large Fresnel lens
RE: Large Fresnel lens
jeanpaul - thank you for the idea. Is this, on a smaller scale perhaps, being done already?
RE: Large Fresnel lens
Any optical design faster than f/1 is usually impractical, particularly for simple optics. So if you want an f/2 design, you're talking about a focal length of at least 200 meters, with a clear aperture of 100 meters. This structure would be too big to steer and would have extremely poor efficiency.
Additionally, the plastics and polycarbonates used in most fresnel lenses usually cannot tolerate continual UV exposure to the sun.
A fresnel lens is composed of an array of prismatic features, which is what allows it to bend light. These prismatic surfaces have to change angle as a function of distance from the center of the optics, which is how normal optics works. A sheet of water will bend light at the same angle across its area, unless you vary the thickness.
TTFN
RE: Large Fresnel lens
But why not use a cylindrical fresnel lens with a bunch of glass or PC cases in prism shape.
You could in this way obtain a sort of greenhouse...
RE: Large Fresnel lens
TTFN
RE: Large Fresnel lens
RE: Large Fresnel lens
I wouldn't even consider water: it can freeze, it can spoil
(algae, bacteria, etc.) Do you even know if it is transparent to IR ?
Do you want to build one unit or mass produce it ? The two
approaches are 100% different !
<nbucska@pcperipherals.com>
RE: Large Fresnel lens
To answer questions and post some final ones:
+ The application requires solar energy from about 5000 squm
+ It could, if built inexpensively enough be replicated several hundred times
to IRstuff
What is your experience with sunlight exposure of PC or Metaacrylate? Does it last days, months or years?
I will be travelling the next 6-8 weeks and not able to participate - please feel free to continue, it has been teaching to me so far. Thank you.
RE: Large Fresnel lens
Honeywell made a solar system with many large flat mirrors
individually servoed but they abandonned it -- I don't know
why.
<nbucska@pcperipherals.com>
RE: Large Fresnel lens
Maybe you can find Large Fresnel Lens from http://www.3dlens.com
RE: Large Fresnel lens
The lens must be between the Sun and the target -- i.e.
elevated. The mirror can be located at ground level.
<nbucska@pcperipherals.com>
RE: Large Fresnel lens
RE: Large Fresnel lens
vr. plane mirrors.
<nbucska@pcperipherals.com>
RE: Large Fresnel lens
To nbucska (Electrical)- to my view mirrors are expensive and unlikely to get less expensive, if compared with Acryl the cost factor for the same collection surface seems to be 1:2 in favour of acryl. Also - consumption of area can be a critical issue and I would assume that while mirrors need thorough constant polishing it should be easier to keep fresnel lenses clean?
RE: Large Fresnel lens
TTFN
RE: Large Fresnel lens
RE: Large Fresnel lens
David
RE: Large Fresnel lens
To SolarDave - can you point to a source for mechanical property data on acryl?
RE: Large Fresnel lens
Sorry 4 delay...
On mirror the dust is worst for it effects the light twice.
<nbucska@pcperipherals DOT com> subj: eng-tips
RE: Large Fresnel lens
Semi-transparent particles tend to diffuse the energy anyway, so they are essentially opaque as well.
TTFN
RE: Large Fresnel lens
Yes but even in the case of front surface mirrors a particle due to its thickness may obstruct more light
on the second pass, especially at more acute angles
of incidence.
<nbucska@pcperipherals DOT com> subj: eng-tips
RE: Large Fresnel lens
David
RE: Large Fresnel lens
RE: Large Fresnel lens
The water can be replaced with alcohol, to avoid algae and has lower density than water, Lavoisier used a giant alcohol lens in the 18th century to melt platinum.
People have mentioned infavourable span to weight ratio for giant fresnel lenses, however i wonder if one could overcome this by using a pressurized plastic dome or balloon like structure..?
RE: Large Fresnel lens
Likewise one could envision pressurized greenhouse like Fresnel structure floating in lakes ?
RE: Large Fresnel lens
http://members.aol.com/stiffcrust/pharos/lens.jpg
RE: Large Fresnel lens
Now compare it with a number of flat mirrors on the ground independently servoed -- the only disadvantage is than
it occupies larger area.
<nbucska@pcperipherals DOT com> subj: eng-tips
read FAQ240-1032
RE: Large Fresnel lens
One possible advantage I am having in mind putting your solar furnace on water is that you could put some stirling engine in the focal point of the furnace, wich will get heated and make helium expand, now the the second chamber of the stirling engine actually runs under water providing active cooling allowing the expanded helium to be compressed agin.
RE: Large Fresnel lens
http://www.nasatech.com/Briefs/Mar99/LEW16662.html
RE: Large Fresnel lens
http://sleekfreak.ath.cx:81/3wdev/VITAHTML/SUBLEV/...
RE: Large Fresnel lens
Steve