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The solar design T-Square is a simple device to represent the sun and greatly aids the design process. My aim is to design better solar cooker reflectors for unattended cooking. Imagine the sun as a giant spotlight shining down. It moves at about 15 degrees per hour across your solar cooker. For a couple of hours the arc path of the sun is pretty close to a straight line i.e. the chord to the arc.
This means that we can use 2 laser pointers on a slider to represent the sun,s motion in the sky. One laser pointer represents the sun at the START of the cook time and the other pointer represents the sun at the END of the cook time.
If you mount the laser pointers on a slider on a T-square, above your model, you can slide them along slider to test how the light rays bounce off of every part of your model! (something that you cannot do with sunlight itself because it hits every part of the reflector at once!)
The t-square and laser pointers together could also be used to design box cooker reflectors to catch more sun with side reflectors to the box!
Picture of the Solar Designer
In the picture above
- the T-Square is outlined in orange,
- the laser pointers are pointed to with green arrows and
- a blue arrow points to the target which is a ball.
- The silvery foil between the spray gun and the styrofoam cup is the reflector.
- Additional details of the device are given a little later and more photographs show the device being used..
- All other items are essentially clutter and were just there.
In this case, the reflector is basically parabolic with strips of material to redirect the light towards the target. The model in this picture is almost correct. It is a half parabolic trough with 6 strips of reflective material to refocus its light onto the ball. (The top of the strips should bend and touch the ball, but I could not hold them in place). Other than that, the model is pretty correct and is good for about 2 hours and 20 minutes of unattended cooking! (In theory!) I set the laser levels to 35 degrees in this case. If you want a one hour cook time, you would set them to 15 degrees. Incidentally an unattended parabolic solar cooker cannot evenly cook for 2 hours and 20 minutes .
Dishes designed for unattended cooking with the t square are NOT parabolic dishes!
Modeling the Solar Cooker
Start modeling with the lasers are in line with the sun at the start and end of its path.
Then slide the laser pointers to plot how the reflectors will focus light as the sun moves during the cooking time.
You can adjust your model a little at a time, like clay animation, a stop motion technique, until you get the desired results. You can make different models of your new solar cooker reflectors and use the laser pointers to see where the light ends up after hitting the reflectors. If the light bounces from your reflector and misses the target, it is a relatively easy task to adjust the angle and size of reflector so that it hits its target.
Modeling additional reflectors
The diagram above shows how you can try adding additional reflectors near the target solar box to increase the unattended cooking time. The additional reflectors bounce the sun light into the solar box. This becomes apparent after 20 minutes using the device! Indeed, people will be able to use it to improve the performance of current parabolic dishes, giving them an extra few minute between adjustments, etc. :Using the T-Square, it should be relatively easy to design better cookit's and to design whole new ranges of solar cookers to better suit individual requirements. You can go for as much simplicity or perfection as your circumstances dictate!
Additional Details of Solar Designer
The cheap laser pointers used to make the device do not have an on off switch. They have a button that you must keep depressed. That button is being kept depressed during modeling by the clothes clip.
The setsquare has degrees marked on it.
It is important to see how it is done.
In the picture above you can just see a laser dot on the bottom of the setsquare.
In this picture you can see the laser spot at 75degrees.
I use Mylar reflective plastic for the models. It is "stuck" to a plastic backing (a thin plastic table mat works) with water droplets from the sprayer.The sticking is fairly easy. I also cut it into strips for the upright part that focuses the light further onto the ball. It is quite the task to keep them in place and that is a part that I have not figured out yet.
The laser point hits the ball (target) and is reflected in the mirrors.
The dots are the laser reflection from the ball
Animation Gif to show the modeling process
I have used the solar design t square to get the clam shape shown in the above picture. The little mirrors are adjusted so that the light from each laser pointer hits the mirror and bounces to hit the target ball. I used clay underneath the mirrors to hold and adjust them.
When the clay mold is completed, the mirrors can be removed, the clay surface smoothed and the material for the real reflector put on the mold and molded to the shape. You can see a video of the earliest version of the designer at http://www.youtube.com/watch?v=xbiVo12kuKA
"Scallop shaped" may be too hard, simpler options are available.
- See Brian White.