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http://www.instructables.com/id/CERC-Green-Solar-Oven/

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CERC Green Solar Ovenby 3point2 on April 15, 2010

Table of Contents

License: Attribution Non-commercial Share Alike (by-nc-sa) .............................................................................

Intro: CERC Green Solar Oven ..................................................................................................

step 1: Supplies and Materials ...................................................................................................

step 2: The Science Behind It ....................................................................................................

step 3: The First Cut ..........................................................................................................

step 4: Create the Reflector Paddles ..............................................................................................

step 5: Assemble the Reflector Paddles ............................................................................................

step 6: Install the Glazing and Reinforce ............................................................................................ 1

step 7: Assemble the Cooking Chamber - Heat Collector ............................................................................... 1

step 8: Assemble the Cooking Chamber - Insulation Layer .............................................................................. 1

step 9: Building the Stand ...................................................................................................... 1

step 10: Test it out ............................................................................................................ 1

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License: Attribution Non-commercial Share Alike (by-nc-sa)

Intro: CERC Green Solar OvenA solar oven is a great way to conserve resources and tap into the wealth of energy that hits the Earth every day. In this Instructable, we will show you how to construa high efficiency solar oven out of mostly waste or scrap parts you probably have lying around your house. The intention here is to use these materials that wouldnormally take up space in landfills for harnessing the power of the sun. In this way, we are not only re-purposing and reducing waste, we are conserving resources.Many people believe that these ovens are novelties and can not be used for anything. The truth is this oven heats up very fast and care should be taken when handinor any contents when at operating temperature. Under spring weather conditions and when pointed properly at the sun on a clear day, it will pass 150C (300F) with10 minutes.

step 1:Supplies and MaterialsFor this project you will need to find:

Several Different Sized Boxes (some very large ones are useful)Clear Packing TapeStyrofoam Packing Peanuts or Shredded PaperRazor bladeBlack Spray Paint (enamel) or Black Enamel Paint in a can (you should not use latex paint)ScissorsPaper ClipsAluminum Foil (heavier and shinier the better)A piece of Glass or AcrylicGlass cutter (if glass is used), a Saw (if acrylic is used)Rubber BandsCan to cook food inShort pencils or dowels which no longer have a useA ruler (yard or meter stick would be best)Pen or PencilsCalculator

Optional:Thermometer Probe to monitor temperature
http://creativecommons.org/licenses/by-nc-sa/2.5/


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Image Notes1. An 8" x 8" x 5" box was used as the cooking chamber in this Instructable


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Image Notes1. Shredded Paper will work as an insulation layer to trap heat. Because papercan be recycled otherwise, its probably best to use the packing peanuts.2. Styrofoam Packing Peanuts make a great insulation material. Because they arenon-biodegradable it is great that you are keeping them out of a landfill!

step 2:

The Science Behind It

Before you begin building your oven, you may be curious as to how one works. You may also wonder why prior ovens you have built did not work very well. Today, ware here to help with a quick explanation.This oven works by concentrating the sun's energy into a smaller area and absorbing it with high efficiency. Parabolic or trough solar cookers work by concentrating tsun's rays. They are more efficient than this linear reflector type but generally only heat one side at a time and can only generate heat in a small point. This oven usepiece of glass, known in the industry as "glazing", to trap heat in a small chamber which has been painted black. The reason the cooking chamber is painted black isbecause this color absorbs all wavelengths of the sun's light. Black appears black to our eyes because none of the light rays are able to reflect back. Because of thisthe energy in the light gets converted into heat which in turn is trapped in the pocket of air enclosed by the glazing. Neat huh?But how do those reflectors work? Well, the trick is the angle that they are pitched. It might seem logical to set the angle of the reflector paddles at 45 degrees (as I hseen many suggest in their instructions) but this is absolutely wrong. If you set the angle at 45 degrees you will create what is known as a retroreflector. It is the samthing used in traffic signs which seem to "glow" at night when your headlights hit them. All the sun's energy which hit reflectors at this angle will be directed right backthe sun. See the illustration for an explanation.The angle you actually want is about 32 degrees from vertical. You can find this value yourself by assuming the sunlight is hitting the collector area in a parallel fashioFrom there, we take the half-angle and get the final spot where the light beam lands. It is important to not make the reflector too big because with a straight reflector itonly possible to get a certain concentration factor. For this oven, it is 5:1.


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step 3:The First CutWe are about to begin. Safety should be the first thought! We will be using razors to cut most of the cardboard. You may use scissors as well but most people finmore difficult. Always remember to ask for help when you need it. Always cut away from your body or hands so that if the blade slips, it will not strike you (or anyone

around you). Also, again remember that this is a real oven which within minutes reaches temperatures that can cause significant burns. Treat it like a real oven whenopening to recover cooked items.

USFand CERC present this as a guideline by which to build your own oven. We do not assume any responsibility or and assume no liability (expressly stated or implas to the performance or safety of this project. Please exercise caution when attempting to build and use this oven.

Now, lets get started.

step 4:Create the Reflector PaddlesYour first goal is to find a (somewhat small) to make the cooking chamber. To make the math simple here, we am going to assume you will find a box with identical silengths. What we mean by this is that where the box opens up, the length is equal to the width. The depth should ideally be no more than the length or width.The reflector paddle is a simple trapezoid with the following special formula. The small upper part of the trapezoid is the same as the width of your cooking chamber bThe wider size of the trapezoid is 2.25 x [cook chamber width] and the height is 1.25 x [cook chamber width. Using these simple multiplications, the reflector will scaleto whatever size you desire. Additionally, it will effortlessly create the desired 32 degree angle talked about in the theory section.Get some foil and tape it at the back to the cardboard with the SHINYSIDEFACINGOUT. Try not to put too much tape on the surface of the reflector side. You willneed to repeat this 3 more times . Easy!


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Image Notes1. An 8" x 8" x 5" box was used as the cooking chamber in this Instructable


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step 5:Assemble the Reflector PaddlesAfter you have 4 reflector trapezoids, start by placing two adjacent with the shiny side facing in and tape along outside the diagonal side as shown in the pictures.Continue this for all 4 pieces and you should end up with what looks like a pyramid with the top missing. If you did this right, the reflective side will be on the inside of pyramid.


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step 6:Install the Glazing and ReinforceNow comes the dangerous part. You will need to find either glass or acrylic and cut it. If you have glass on hand, you need to borrow or purchase a glass cutter whicwill allow you to score and snap the glass to the desired size to fit perfectly into the small square of the pyramid as shown. If you have never worked with glass, it isprobably a lot safer for you to work with acrylic. Polycarbonate can be used as well but there will be a 2.2% loss in oven efficiency. Cut the acrylic to the desired size tape in to the reflector. At this time, add some tape around the edges to strengthen the easy to tear foil in preparation for the next step. It is okay to have a layer of taon the reflective side near the edges.

step 7:Assemble the Cooking Chamber - Heat CollectorLets focus back on the cooking chamber. Grab some more foil and gently crumple it to obtain a textured surface. You should not crumple it to the point that holes stadevelop. When you straighten it back out, hold it up to the light to verify that it is not full of holes. Repeat this step as many times necessary to cover the inside of thebox. From here, tape the protruding foil down.

You now have to paint the collector black. You must use a paint which can handle higher temperatures. Latex paint is not acceptable. Try to find a matte or flat finishblack enamel paint. You can use a spray paint but be sure to get one without CFC's which can harm the ozone layer. Also, spray paints will require many thin coats bcan produce and easier to apply and more even coating. Brushes work just as well because we are actually NOT looking for a smooth finish. In the end, be sure thepaint is VERY black since there are many times it can look tinted and will reduce efficiency greatly.

After the paint is dry, fashion some clips to hold everything together. Grab your rubber bands and paper clips and connect them in a paperclip-rubber band-paperclipsegment. Depending on the size of your oven, you may need one, two, or three clips per side. Below, we show an example of one and two clips per size. On theCooking chamber, push one end of the paperclip through the cardboard to anchor it. Place the reflector on the cooking chamber and stretch the rubber and to clip theother paperclip to the edge of the reflector. Repeat for all sides.


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step 8:Assemble the Cooking Chamber - Insulation LayerFind a box about 2-3 inches (5 - 8cm) larger on all sides than the cooking chamber. Fill the bottom with a layer of foam packing peanuts (or shredded paper) about 3inches (8cm) thick. Place the cooking chamber on the peanuts and center in the box. Proceed to fill the box with packing peanuts and tape secure.

The last picture shows one of the two optional stands you can build. If you find a box just slightly large than the insulation box, you can build a very simple but somewflimsy base. Continue on for detailed instructions on the base.


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step 9:Building the StandNow that the oven is ready to go, you need a base stand so that you can easily and accurately point it at the sun.

NEVERSTAREDIRECTLYATTHESUNTODETERMINEWHERETOPOINT!!!!

One option is to build a simple stand out of a box slightly larger than the insulation holding box.

Because this design was not as stable, we decided to show an option to a more complicated but far steadier box frame design.

The first two pictures show the easy way of building a stand out of a single box and putting pencils through as pivots. Alternatively, you can create a box frame by findlong rectangular pieces of cardboard and scoring the board with a knife creating 4 equally spaced panels. Tape this together to make a square-tube of sorts. You canit with more cardboard to stiffen if desired. Tape them inside a larger box and push the pencils through. This design is a little more elaborate and is customized for evbuild. Because of this, we can not really go into greater detail about how to build it.


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step 10:Test it outNow that your oven is ready, here are some final thoughts. Cooking containers should also be black so consider finding a can and painting it black as well. Because paint may need some time to cure and may release extra solvents (read: bad smell), it is probably wise to run the oven a full temperature a few times without food in itclear any smell. Find a place with a clear, unobstructed view of the sky. The time of day does not matter as much as one would expect. We easy got past 115C(240F) in minutes at 6pm. Align to the sun by pointing in the general direction and tilting/turning until no shadow from the sidewalls could be seen in the cookingchamber. Remember that you need to adjust this every so often for optimum performance. Use a meat thermometer or temperature probe to ensure the position is

perfect and the hottest temperatures are being achieved. Lastly, if your food needs to be kept flat and the tilting might cause a spill, you can push a wooden dowel, piof metal, clothes hanger rod, just about anything through the middle of the chamber to be able to hang a gondola for food. This will allow you to boil water even whensignificantly tilted.

So there you have it: an oven that can be built out of things normally destined for a landfill. Be sure to post your best temperatures in the comments below. Enjoy anthank you for reading.

-University of South Florida, Clean Energy Research Center Team

design and writeup by: mec 2010


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