Design an exotic reflector for unattended solar cooking. Your design might get used worldwide.
http://solarcooking.wikia.com/wiki/Solar_design_T-Square is the main page
I put in a new step 5 today (November 17th) with pictures to better explain it.
http://solardesign.ning.com/photo/albums/solar-design-tsquare (feb 9th) has pictures of models I made recently for 2 hour and one hour reflectors.
People say "why do it?" and "it cannot be done". Now companys in the western world are using carbon offsets to pay for the manafacture of parabolic solar cookers in India. They are even paying people to use them to cook their meals!
(In this way Solar energy is substituting for firewood and lets the forests regrow!)
But problems with light getting flashed in peoples eyes and having to constantly move the reflectors are being reported. These are BIG problems.
A dish for unattended cooking would alleviate the problems substantially.
It CAN be done! Check 5 minutes into this video for a (Probably patented) (and too complicated) design! http://www.youtube.com/watch?v=TSMzKg6fwJ8 and pause it at 5min 56 seconds in for the shape.
It is the tube horns that I am interested in. I believe 2 horns, lined up with the path of the sun is likely to be pretty efficient.
Here is another link with a picture to help get the idea
http://en.wikipedia.org/wiki/Holmdel_Horn_Antenna When you look at that picture, do you think of solar box cookers "with ears"!?
Please note that I use image notes extensively to explain
The method I choose is similar to "claymation" in that it will produce the grand design by a series of little steps. In this case, 2 laser levels are used to simulate the suns rays. If your design is to be unattended for 2 hours, then the laser levels shine at angles 30 degrees different to each other.
Step 1: The Design Process on One Page
Step 2: Compromise
It makes for light and easy to move apparatus.
Step 3: The Reflective Dish Problem
This is a back to the drawing board experience!
Step 4: Concepts
If only one hits the target, then you have to adjust the angle of the strip of reflector until it hits.
Preferable it should hit with just one bounce. However it may be worthwhile to have it bouncing a few times if it increases the reflector size sufficiently.
Step 5: How to Set Up the Lasers and Model
I include one drawing of how it can be done with the "sliding model" and I will add a diagram of the "edge of sliding shelf" concept later. (Just 2 different ways to achieve the same result).
I do not know which will be best in the long term.
Step 6: My System and My Model
I also show something of the start of a model. Here I ran into problems because I do not have suitable strips of material for the backing of the reflective mylar. But not bad progress, i think.
See the photo's for the progress. I use image notes to explain more of the detail.
Step 7: You Only Need to Make a Quarter of the Design!
When the shape becomes clear it can just be transfered to the other 3 quarters.
This means that the design process is not as tough as it first seems!
Step 8: Strips or Slices?
This might work but it is probably harder to handle cuts that get wider the further they are from the inside.
Strips all the same width are probably easier to handle because you can make standard pieces and wedges to keep them in place after you adjust them.
Also, in the design phase, gaps may be fine. It may even be helpful as you try to find the complete shape.
Step 9: Starting Your Model
From making the model, I though of a few things.
1. It is sometimes hard to see where the reflection bounces on the ball. Sometimes it is on top, bottom or side.
2. No ball is needed if you just make a round hole at the back of the reflector. That might be the easiest way because then all you have to do is have a white sheet of paper over the hole and you can always see the laser dots on the paper if it is properly adjusted!
First of all I got a red ball to represent the cooking pot. This can be suspended a few inches above the table or screwed into the table at that height.
Below the cooking pot, you must have your strips of reflective material laid out. The ideal material might be a thin plastic with reflective material stuck on it.
I might drill holes in the bottom of all the strips and attach them all to a center using a pin or small nail.
I still have not figured out how best to keep the strips in position as I and after I adjust them to the laser points.
I show a procedeure to adjust the strips in the image notes.
If you are willing to have 2 or more bounces of light and (if you want to produce a more exotic beautiful shape), Then I suggest you start at strip 10 and work backwards. As your reflections start to go out of range and start missing the target, start using strips 1,2, etc to redirect them!
In this way, you both enlarge the reflector shape and get an exotic and perhaps beautiful shape!
Step 10: Refining the Shape
Step 11: Tradeoff Time. Sine Rules and Bounces.
And its average power over those 2 hours will be 98% or better WITHOUT HAVING TO BE THERE TO ADJUST THE DISH. But of course, you might have to do 2 bounces in some places.
With a 3 hour dish, the sine goes from .924 to 1 and back to .924 so a lot more loss. Perhaps you only get 95% over the 3 hours. And with 4 hour dishes, you go from 86.6% to 1 and back to 86.6%
So you get tradeoffs depending on how unattended you want your dish to be.
At some points your design may have 2 or even 3 bounces of light before you get to the target.
You can assume 10% loss at each bounce. 1 bounce is the same as a normal parabolic dish so first bounce does not count. 2 bounces is 90% and 3 is 0.9 X 0.9 = 0.81 4 is 0.9 X 0.9 X 0.9 = 0.729
so we get tradeoffs whereever we go!
Hopefully people will use this idea to design dishes with the right amount of tradeoffs for their own situations.