Survivalism & Self Sufficiency Topics > Food Preps

Fresnel Lens for Solar Oven

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JAG2955:
My dad had a 12" square one from when he was a science teacher that I would play with a lot.  I do believe that I tried to heat a pot of water with it once, without much luck.  It would melt plastic army men like a champ, though.  Wear your welder's goggles, the focal point is extremely bright.

mangyhyena:
Fresnel lenses have several uses for self sufficiency.  At a web site called Green Power Science, large Fresnel lenses are sold.  They can be bought in a tilting frame, much like a full length mirror frame.  If you want one for free, you can look on craigslist for old big screen TV's people are giving away.  Those TV's have a Fresnel lens in them.  If you're willing to haul the TV away, you can get your big lens for free and frame it yourself.

You can purchase one here. http://greenpowerscience.com/SHOPFRESNELHOME.html

These lenses are extremely hands-on, meaning you can't just set it and forget it; you have to be there to operate it to ensure that nothing catches fire and to move it as the sun crosses the sky.  But, the sun is free and if you're willing to spend the time using one, there are a lot of things you can accomplish with it.

As mentioned already, you can cook with them.  I watched a video of a woman who used one to cook scrambled eggs in a matter of seconds, as well as another where a pasta dinner was cooked using only a Fresnel lens.  They are excellent fire starters, of course, capable of lighting a 2X4 in a matter of seconds.  They can easily distill water quickly by focusing the beam on a heat exchanger.
There are YouTube videos of people doing these things.  Green Power Science has quite a few of them up for viewing and I'd suggest viewing those.

A few things that I haven't seen done yet, but that should be possible, are:
Using a Fresnel lens as the heat source in a wood or coal gasifier.
Using a Fresnel lens as the heat source for a TEG, (thermal electric generator)
Using a Fresnel lens as the heat source to flash steam water, the resulting steam used to power a micro turbine to produce electricity or do other useful work.
Using a Fresnel lens as the heat source for distilling fuel alcohol.
Using a Fresnel lens to heat rocks or clay pots full of sand during the day, then bringing those hot rocks or clay pots in at night for a radiant heat source.


I think survivalists and preppers need to really look into the uses of a Fresnel lens for emergency purposes.  Who knows, with enough information and experimentation, maybe we can figure out how to use Fresnel lenses in a more set-it-and-forget-it way.  Seems like using a solar tracker is a first step toward that.  And perhaps a metal shield that sits much closer to the lens than the focal point, stopping the beam from focusing too hot, might make these things safer, in terms of accidental fires starting.

Nicodemus:
While not a fresnel lens, but a solar collector, here is the power of two square meters of sunlight when focused.

Take that you stupid rock!  :D

http://www.youtube.com/watch?v=z0_nuvPKIi8#

mangyhyena:

--- Quote from: Nicodemus on November 20, 2010, 01:27:30 PM ---On a similar note, a long parabolic reflective trough with a focal point directed at a black tube filled with water might prove to be an easier method to heat water for purification. If the trough is parallel to the path of the sun it might collect enough light all day long without any need to refocus for light intensity. I don't know if this would produce enough constant heat to purify water, but this is how some solar hot water heaters work.

--- End quote ---

You're right, for heating a lot of water, a parabolic trough is the way to go.  Length of trough, how reflective the reflective coating is, and flow rate of water will determine how hot the water gets.  A parabolic trough gets plenty hot for water purification. A parabolic trough makes a focal line that runs all the way along a collector tube, rather than focusing down to a little pinpoint.  That focal line running along every inch of the collector is the reason a trough can heat a large volum of water.

The beam from a Fresnel lens can be bounced off a mirror. I saw a video where the beam was reflected back up and onto the underside of a pan, cooking eggs really fast.  It can also go through CLEAR glass, so maybe it could jump start or enhance the performance of a standard solar oven.  If the glass isn't perfectly clear the beam will shatter it, so be careful.

Falling_blue:
Just got a free non-working rear projection tv off of cragslist, built a frame and stand for the fresnel lens and am currently cooking cornbread in a dutch oven.  Got a temp ~300 in the dutch oven before I started so it should turn out well.  I plan on finding a mirror to bounce the spot up to a grill for pans but couldn't wait to cook something with it.

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