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Parabolic Solar Cookers Page 3 of 5
Why Use a Parabolic Shape?			Some people prefer to design custom shaped parabolic cookers rather than starting with a satellite dish. Click on the links provided below to access interactive graphs that allow you to model custom parabolic curves and 3D paraboloids. Graph 1: Graph 2: Graph 3: Graph 4: Once you have decided which curve and 3D representation you wish to model your parabolic solar cooker you can copy the 2D cuve image onto a transparency. That image can be projected onto a wall where it can be traced and used to create a template. You may prefer to use the parabola drawing tool referenced near the top of the last page.
When a three dimensional parabola (i.e. a paraboloid) is aimed at the sun, all the light that falls upon its mirrored surface is reflected to a point known as the focus. If a black cooking pot is placed at the focus it will absorb the light's energy and become very hot. A satellite dish is an example of a parabaloid that can be made into a cooker. Parabolic Solar cookers heat up quickly and are used like a standard stovetop range to sauté or fry foods, boil water, or even bake bread. They can also be used to generate steam, power sterling engines, crack water to produce H2 gas, and even plasma matter. It is easy to see in today's world that this shape is successful in its use. The parabolic shape can be seen in satellite dishes, radio towers, and yes, even in solar cookers around the world. It is simple to say it works, and just as simple to understand how it works.	.Diagram 1 shows the unique reflecting properties of the parabola .Click on the diagram to activate an interactive graph demonstrating how to vary the height of the focus of the parabola by altering the equation the curve and thus changing the relative shape of the parabola. Diagram 1: Click on diagram . Diagram 2: Focus Height Click to Enlarge Diagram 3 attempts to give an intuitive understanding of deep focus vs shallow focus parabolas. Each curve represents a different arch length of the same parabola, at varying magnifications.	Diagram 3: The curve on the far left is an enlargement of the vertex region of the curve of the far right. Each curve has the same focal point. Some people prefer the "bowl" shape of a deep focus paraboloid rather than the relatively flat satelitte dish. This deeper bowl shape helps shelter the cooking pot from the wind. It also causes the pot to be heated evenly from all sides instead of just the bottom. The bowl shaped paraboloid can be aimed at the sun with out the use of a stand or tracking device. Click on the images of deep focus paraboloids shown below to see enlargements.
Click to Enlarge	Click to Enlarge	Click to Enlarge	Click to Enlarge
Click to Enlarge Bart Orlando instructing an HSU student in mapping facets to be cut from an aluminum sheet Click to Enlarge A 4x8'sheet of mirror finnished, anodized aluminum with mapped facets to be cut Click to Enlarge Professor Mort Scott demonstrates how to cut mirror finnished aluminum with a beverly shear at the HSU sculpture lab	How to Build a Parabolic Cooker
	One of the easiest beginnings for a parabolic solar cooker can be found in thousands of backyards across the United States-the satellite dish, from the large C-band to the small digital dish. What happens to these relics once they are discarded? They are large and awkward and not easily recycled. Building your own solar cooker is a great way to reuse these parabolic-shaped units while reducing waste in the landfill. Once you have decided to build your parabolic solar cooker it is important to find a dish that is as concave a s possible in order to have an accessible focus point to cook at. Next, measure your dish and locate your focus. If you have a satellite dish with the receiver/antenna still	attached, your work is done for you since these are located at the focus of the dish. However, if you obtain one without it, you will need to make some simple calculations. Use the sample problem on the next page to guide you through this process. The focus can also be found by direct observation after you have lined the dish with a reflective material. Hold a piece of cardboard close to the center of the dish, then move it up and down toward the sun and back. A circle of light will appear on the underside of the cardboard. When the circle is smallest, the position of the focus is found. The most popular material used to line the dish is a reflective, mirror-finished, anodised aluminium sheet. These are cut into Click to Enlarge Counter weight system made from used weight lifting equipment Click to Enlarge A gimbled pot mount structure made from used bike rims allows the pot to remain level	narrow triangular facets no wider than ten inches, then riveted to the dish. Sheet metal supply companies can be found online or in the phone book. Riveting supplies can be found at a hardware store. The pot stand, located at the focus, can be made from a used 12" bicycle rim attached to pieces of metal tubing so that the rim and cooking pot can be levelled. Place a grate across the rim to support the pot. Remember while you are constructing your cooker, NEVER STARE DIRECTLY into the cooker once you have installed your reflecting material. ALWAYS WEAR UV PROTECTIVE DARK SUNGLASSES WHEN WORKING WITH YOUR COOKER!
	Click to Enlarge HSU student riveting aluminum to dish. Click to Enlarge Garrett McSorley and Bart Orlando attaching a salvaged satellite dish mount pole

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