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is this fresnel lens suitable for high temp solar oven?

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Posted by Eric Jones on August 24, 2007, 4:28 pm
 
I desire to build a solar furnace with a fresnel lens.  After some
searching, I came across this candidate:

http://www.goldmine-elec-products.com/prodinfo.asp?number=G16400

The only question I have is whether or not this highly concentrates light,
or is it a diffuse concentration?  Some info I've come across recently
suggests that not all fresnel lenses make ideal solar ovens because some
types have too wide/ diffused focal point.

If anyone has used this lens and can tell me about it's solar collection
abilities, please share.  Most importantly, how tight the focal point is.

Thanks in advance,
Eric



Posted by Anthony Matonak on August 24, 2007, 4:56 pm
 
Eric Jones wrote:

I don't have this lens but from the report of "a two inch" focal point
I would say it's good enough. You're not going to get a true point from
the sun because the sun itself is not a point. The best you'll get is
an image of the sun.

Have you considered building your own? A multi-element reflector or
parabolic dish isn't very difficult to build and you and make it any
size you like.

http://graffiti.virgin.net/ljmayes.mal/var/parabola.htm
http://www.solarcooking.org/plans/default.htm
http://amasci.com/amateur/mirror.html

Anthony

Posted by Duane C. Johnson on August 24, 2007, 5:33 pm
 Hi Eric;


 > I desire to build a solar furnace with a Fresnel
 > lens.  After some searching, I came across this
 > candidate:

 > http://www.goldmine-elec-products.com/prodinfo.asp?number=G16400

Looks pretty good.

 > The only question I have is whether or not this
 > highly concentrates light, or is it a diffuse
 > concentration?

The add says the concentration zone is about 2".
That's pretty good. The concentration ratio is
about 400X. This is a bit diffuse but quite
workable.

The solar power captured is about 900W less the
light losses in the lens, maybe an efficiency of
about 75%, or about 650W.

A perfect lens with a 31" focal length would have a
solar focal zone of about .27". This would imply a
concentration factor of about 22000X.

 > Some info I've come across recently suggests that
 > not all Fresnel lenses make ideal solar ovens
 > because some types have too wide/ diffused focal
 > point.

 > If anyone has used this lens and can tell me about
 > it's solar collection abilities, please share.
 > Most importantly, how tight the focal point is.

Of course, a dish will work better and be cheaper,
possibly free, than the Fresnel lens. Especially in
larger sizes.

 > Thanks in advance,
 > Eric

Duane

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