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Ambjörn Naeve discovered that if you put 2 parabolic trough concentrators in series at the right distance appart, you can get a burning point of light. Professor Naeve has given me permission to use his images here to show his device.[[File:PointFocus-Discovery.jpg|thumb|Click to enlarge]] He showed that by bending 2 pieces of reflective sheet material you can mimic a parabolic trough. It is much easier to bend 2 pieces than the bend and cut and bend and cut many times to make a parabolic dish.
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Here is the proof[[File:Pointfocus-proof.jpg|thumb|Proof, click to enlarge]]
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Here is Naeve using the device to melt copper![[File:Pointfocus-melting_copper.jpg|thumb|Click to enlarge]]
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Here is Naeves diagram of a Solar wheelbarrow
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:'''See also:''' [http://solarcooking.wikia.com/wiki/Parabolic_solar_reflectors#Using_Two_Perpendicular_Troughs_to_Simulate_a_Paraboloid Parabolic solar reflectors - Using two perpendicular troughs to simulate a paraboloid]
[[File:PointFocus-wheelbarrel.jpg|thumb|Click to enlarge]]
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Ambjörn Naeve is a professor at the Royal Institute of Technology, in Stockholm, Sweden.<ref>In Swedish, the name of the institute is "Kungliga Tekniska högskolan". Its initials, KTH, are to be found in many of Naeve's files.</ref> In the 1970s, he discovered that if you put two parabolic trough solar concentrators in series at the right distance apart and in the right orientation, you can get a burning point of light. He has given permission to use his images here to show his device. He showed that by bending two pieces of reflective sheet material you can mimic a paraboloidal reflector. It is much easier to bend two pieces than to bend and cut and bend and cut many times to make a parabolic dish.
I believe that Ambjörn Naeve made a great breakthrough back in the 1970"s when he discovered and worked on these concepts.
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Here is the proof.
http://kmr.nada.kth.se/wiki/Main/PointFocus is his story of the discovery and how he tried to spread the knowelege.
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[[File:PointFocus-Discovery.jpg|thumb|Diagram of device.]]
For me, I think the naeve cross holds the potential for people
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[[File:Pointfocus-proof.jpg|thumb|left|Proof.]]
to design a combined trough solar cooker with a 2 hour cook time (or a 3 hour cook time)
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{{clr}}
(Which would be excellent in its own right) and then
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Here are more images. (Click on the icon at the bottom-right corner of any image to enlarge it.)
"reverse engineer" a dish from it.
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[[File:Pointfocus-melting_copper.jpg|thumb|left|To demonstrate the high temperatutes it can reach, here is Naeve's device melting copper!]]
This combined trough or dish with a 2 or 3 hour UNATTENDED cooktime
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[[File:PointFocus-wheelbarrel.jpg|thumb|Naeve's diagram of a solar wheelbarrow, which holds the troughs in proper alignment. The red lines represent rays of light being focused.]]
would be a wonderful breakthrough for solar cooks all over the world.
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{{clr}}
Brian White
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Unfortunately, the Naeve Cross does have disadvantages. Compared with a paraboloid, more mirror material is needed. Also, since, the light is reflected twice, more of it is lost. The device does not share one of the main advantages of simple trough cookers, their tolerance of movements of the sun parallel to the length of the trough. This can allow a trough cooker to work for hours every day without any need for tracking the sun. But movement of the sun parallel to the length of one trough of a Naeve Cross is perpendicular to the length of the other, so the Naeve Cross has to be moved continuously or frequently to track the sun, like a paraboloid.
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Nevertheless, Naeve's device is potentially very useful. [http://kmr.nada.kth.se/wiki/Main/PointFocus Here] is his story of the discovery and how he tried to spread the knowledge.
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There are now commercially available cookers that use the Naeve Cross principle. See: [http://www.prosolartec.com/the-invention.html]
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== Footnote ==
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<references/>
 
[[Category:Solar cooker designs]]
 
[[Category:Solar cooker designs]]

Latest revision as of 04:58, March 9, 2015


See also: Parabolic solar reflectors - Using two perpendicular troughs to simulate a paraboloid

Ambjörn Naeve is a professor at the Royal Institute of Technology, in Stockholm, Sweden.[1] In the 1970s, he discovered that if you put two parabolic trough solar concentrators in series at the right distance apart and in the right orientation, you can get a burning point of light. He has given permission to use his images here to show his device. He showed that by bending two pieces of reflective sheet material you can mimic a paraboloidal reflector. It is much easier to bend two pieces than to bend and cut and bend and cut many times to make a parabolic dish. Here is the proof.

PointFocus-Discovery

Diagram of device.

Pointfocus-proof

Proof.


Here are more images. (Click on the icon at the bottom-right corner of any image to enlarge it.)

Naeve Cross solar concentrator

To demonstrate the high temperatutes it can reach, here is Naeve's device melting copper!

PointFocus-wheelbarrel

Naeve's diagram of a solar wheelbarrow, which holds the troughs in proper alignment. The red lines represent rays of light being focused.


Unfortunately, the Naeve Cross does have disadvantages. Compared with a paraboloid, more mirror material is needed. Also, since, the light is reflected twice, more of it is lost. The device does not share one of the main advantages of simple trough cookers, their tolerance of movements of the sun parallel to the length of the trough. This can allow a trough cooker to work for hours every day without any need for tracking the sun. But movement of the sun parallel to the length of one trough of a Naeve Cross is perpendicular to the length of the other, so the Naeve Cross has to be moved continuously or frequently to track the sun, like a paraboloid.

Nevertheless, Naeve's device is potentially very useful. Here is his story of the discovery and how he tried to spread the knowledge.

There are now commercially available cookers that use the Naeve Cross principle. See: [1]


Footnote Edit

  1. In Swedish, the name of the institute is "Kungliga Tekniska högskolan". Its initials, KTH, are to be found in many of Naeve's files.
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