Use the Scientific Method to Test the "Scientific Method"!

The concept shown in the link (one parabolic trough focuses solar energy onto a line segment, and a second parabolic trough supposedly focuses this line segment to a point) doesn't quite work in the simple form shown. The basic problem is that the second reflector, being curved, does not lie along the directrix of the first. In this example, the light also diverges upward and downward after encountering the second reflector. There might be some ways to fix this, but they too might require compound curvature.

But don't necessarily be defeated by this. Either a parabolic trough or a conical reflector will focus energy onto a line segment, which is suitable for a heat collection pipe. (Focusing to a point gets you several thousand kelvins, which might just melt any point collector you can devise; but focusing to a line can get you a few hundred kelvins, which should be promising, such as for a boiler or Stirling engine.)

I think you may be on the track of a useful idea, but just in need of refinement. In particular, I think it conceivable to devise a simple system with basic clock-drive solar tracking. I haven't worked on it enough yet. But if this is true, there could develop some DIY technologies suitable for off-grid and second/third-world use. I hope to see some interesting ideas arise on this forum.

The guy is a mathematician and there are about 5 videos of it working online. Remember the scientific method? So how can you claim that it does not work? Where is your proof?

Here is one video of it working

http://www.youtube.com/watch?v=FYzgYI9_h6s&feature=channel_page and his link at the side

http://kmr.nada.kth.se/wiki/Main/PointFocus gives more details about the discovery.

And he published his proof over 30 years ago. The focal line of the first lies on the directrix of the second. I, myself am not that interested in 2 troughs to make a burning glass. I am much more interested in useing them as a design factor in making better solar cooking dishes and combined troughs with long cook times. Dismissing the concept "Out of hand" is potentially dismissing a great tool for building better solar devices.

Brian

Please excuse me, but I did not dismiss this concept out of hand. I suggested it was a good idea with considerable potential, though in need of refinement (or so I thought at first.)

Thanks for correcting my mistake; I got hung up on the focal line and confused it with the directrix. The video explained it better than the drawing alone.

As before, good luck with this.

Sorry and Thank you very much for responding again.

I think that the explanation needs better translation to English. The guy is swedish so he is working in his second language. I did not understand some of the terms he used.

If anyone has good explaining skills, a good place to translate would be on the solarcooking wiki. I have been asked to explain it further there, but to be quite honest, I do not understand it very well. It IS released under a community commons licence so no fears of reprisals if you do a good explanation or copy his drawings.

Brian

I'm not sure of your point. I experiment all the time. Always have and always will (at least till the little men in the white coats come for me). I can make a decent parabolic reflector in less than an hour that will cook food (say 400-500K). Or, I can simply buy a cheap one for less than $5 (US). A linear parabolic is even easier.

But, anyway, go into manufacturing your idea. You don't need to restructure the whole system to get that done. Just do it.

You totally miss the point. Can you make your parabolic reflector cook food for 1 or 2 hours unattended? Thats the point and thats the problem that needs to be solved.

It is one of those "boldly go" problems that engineering and science is supposed to be all about.

You can get dozens of templates for parabolic dishes online. But why bother? They have to be adjusted every 15 minutes or so. With all the brainpower available, it should be easy to twist the arms of smart people (Not me) to get them to do something that will be useful to starving people in poor countries. And if you do not care about the people, remember that their alternative to solar for cooking is wood for cooking. And if you do not care about the wood, the alternative to starvation when all the wood is gone is a one way ticket to YOUR country where they will take away YOUR job and you will lose your house and your car.

Maybe we can harness zenophobia for good?

Cooking food is about watts transferred into the food, not about reaching 400 or 500K.

I do not know what motivates people but maybe one of the motivation factors are above?

I have long ago found out that if I do something new, nobody gives a crap. It took 20 years until someone with a little curiosity made a pulser pump. First I had people getting on their high horses saying that it cannot work. A few years later, it was, "it works but nobody tested it because they know it will not be efficient enough". Incredible stuborness is at work here. Pathological stubborness. We need to factor in this incoherant stuborness into our system.

I got to convince "smart" people that it is in their interest to do this stuff.

People listen to smart people. Will some of the smart people listen to me?

No, I don't miss the point. I'm afraid you have missed the point that is a fundamental problem with a solar reflector that does not require aiming. Do you have a working model?

It is not a fundamental problem at all. The cooking pot has area. With the right curve to the dish, you can focus one half of a dish near the top of the pot and the other half near the bottom. As the sun moves, the focus at one side moves up and at the other side moves down so you can get up to 4 hours of cooktime.

http://www.youtube.com/watch?v=uX9Z-nsUHiA was my attempt to explain it a year or so ago.

(snipets of that video plays on the trams in Zurich as part of an engineering round the world video).

Problem, It works great along the path the sun takes across center of the dish, it fails at the sides.

The solution is a dish with a shape like 2 upcurled leaves (Alighed with the path of the sun).. The sides of the leaves are curled up too.

I do not have the mathematics to solve the problem. Perhaps I can solve it with trial and error on art of illusion.

These dishes, if ever designed would probably be very user friendly and could be stamped out in the millions.

Anyways, the deeper you look, the more you see.

One way to get people to experiment more is to make experimenting easier. A low cost optical simulation program would allow an experimenter to configure reflectors in all kinds of shapes and measure the results very quickly. A wind tunnel simulation program for the masses would make it easy to setup all kinds of shapes and arrays of wind energy capture devices, and test and measure their efficiency. Other low cost simulation programs would encourage inventors to 'experiment' a lot before building a real prototype.

There IS a low cost optical simulation program. I started with art of illusion modeling software early this year. At first, I got great help in their forums and a guy donated a "scene file" to me. Over time, I added models of different dishes, and a camera flying overhead (to take a sun's eye view) and changed things quite a lot. Anyone can download my new scene file, fire up art of illusion, and add their own models or modify the sun's movement . One goal is to have a light mimicking the sun moving correctly so that you can show how the shadows would go on any given day at any given latitude. A "sun engine". That would be incredibly valuable right now to landscapers round the world!

And those in the art of illusion forums know how to create "fog" to show how the light spreads and concentrates from mirrors. My problem is to convince people that this is worthwhile!

NOBODY has joined the group I started for this work. I use ning because it accepts .aoi scenefiles easily. I had earlier versions at instructables.com but the scenefile extensions used to change to .temp so bad for storing them.

http://solardesign.ning.com/ I have links to about half an hour's worth of explanatory video there too. So that is considerable effort.

(And some of this video got praised in the art of illusion forums for explaining concepts very well). http://sourceforge.net/projects/aoi/forums/forum/47782/topic/2915545 is the thread where I got the most help. You can get a lot of help at art of illusion homepage too of course. I like it because the main views are elevation, plan, endview and perspective view.

I made a movie to compare 4 different cooking dish shapes and their likely efficiency and it is at

http://www.youtube.com/watch?v=IIRhNRk_0js That was only possible because I had the art of illusion software. I do not believe anyone else in the world has shown the comparison.

And that was with my primative skills. Art of illusion is capable of much more. Free download, full program, nothing crippled and it works on windows, linux and on my netbook in limping linux.

A bunch of people have basically labeled me as a nut for trying to design a reflector for unattended use. BUT I can now point to other people doing it. (People way way smarter than me too!)

Bill Gross has a video at http://www.youtube.com/watch?v=TSMzKg6fwJ8 and if you start 5 minutes in to the video you will see that I am NOT the only person thinging about this. (Gross's design is probably patented and it is seriously "overbuilt" in my opinion anyway).

I am starting to write an "instructable" today about how to use a almost "claymation" technique to design reflectors for solar cookers so that they can designed for 2 3 or 4 hours of use. I will use 2 laser levels to simulate the sun shining on the reflector. In the first design, I will have the lasers angled at 30 degrees and coming to a point. The lasers will be allowed to move up and down on a stand but not allowed to twist. They will be alligned with the long side of the table.

Meanwhile underneath on the table there will be the model of the pot and 1/4 of the reflector. (You only need 1/4 because there is symetrical ballance to the reflector) Your model is on a rectangular sheet of material and you move the sheet around on the table using a set square to keep it alligned with the edge. It needs to be clamped when you adjust the reflector. The reflective material is somewhat springy and is cut in strips radiating from the center. Adjust the reflector so that the spot is exactly shining on one point of it. Twist the reflective material so that 2 spots from the spot bouncing are produced on the target. That means that all the sunlight for 30 degrees will hit the target. (This is to design a reflector for 2 hours of unattended solar cookingl)

Readjust and repeat until your shape becomes evident. Several good solar cooking shapes can be designed with this method.If you take a parabolic dish as 100% efficient (but you have to move it 8 times in 2 hours) if you design the dish for unattended cooking to have one bounce of light from everywhere to the cooking pot, it will be over 98% efficient over the 2 hours! So you lose 2% but save on 2 hours of labour every time you cook!

Brian

To solve the solar heat problem try solarfire.org , they provide solar dish plans that can be made from scrap. I don't know how frequently they have to be aimed, but their purpose is the same. The plans are scalable.

No, because the solar fire stuff has to be aimed very frequently. And no, because it does not solve anything. Most people just rehash the same old stuff. Solar fire are just rehashing. Nobody is redesigning the dish to make the operation safe. Have you ever worked with a solar cooker?

Biggest problem? Getting flashed in the eyes with the sunlight.

And that even happens with popular gso solar cookers. A lot!

Parabolics and gso also have a freaky second order focus which can be 8 or 10 ft away from the first focal point.

Thats part of the reason I tried making "compound" parabolic dishes.

Solutions, tracking or design the dish for unattended use.

Tracking is far easier on equatorial mount (also called polar mount).

90% of the solar stuff that you see online is copycat gimmics.

We should be designing to solve problems not copycatting.

Brian

http://cr4.globalspec.com/comment/429610/Re-Stationary-Solar

here is an idea that seems somewhat relevant. it may be the same as "The focal line of the first lies on the directrix of the second."

Chris

It might have merit, The track might have to change every few days and that might be difficult. Normally reflectors are mirrored and they do not use lenses that much. (Too heavy).

Some Windmills in Holland could be moved by hand when the wind changed direction so it should be possible. A track is a whole lot bigger structure than a hinge, though.

I would like to know some scientific methods.

well, this is my untested but rejected idea concerning people centric solar thermal, (i think photovoltaic is a waste of sunlight). my idea is to bend the light, and do away with moving the troughs, manually or diy heliostat. imagine a cone, consisting of multiple solar tubes, (the kind used to bring sunlight into an interior room). point this array at the high noon suns' position. the center tube would be unbent, each succeeding ring around this would have the appropriate angle elbow to bring the light to bear on a fresnel lens. the focal point of the lens should be hot enough for steam power, or adsorption refrigeration.