Thursday, August 20, 2015

How to Make a Solar Oven

Learn how to make a solar oven that works beautifully, is built to last, and costs less than a purchased solar cooker.
By Eric Smith
October 2011 Web
The following is an excerpt from "DIY Solar Projects" by Eric Smith (Creative Publishing, 2011). 
Solar ovens are simple devices that capture heat from the sun with a reflective surface that's angled or curved towards a cooking pot. Because they can be easily made from cheap materials like scrap cardboard and tinfoil, they are widely used in areas of the world where trees and fossil fuel are scarce or expensive. Once made, they can be used to cook food and boil water in a reasonable amount of time for absolutely no cost.
There are dozens of possible designs; some angle the rays down into a small center area, while others focus the rays upward toward the underside of a pot, like a reversed magnifying glass. You can also buy portable solar ovens assembled from polished metal online—they're great equipment for camping. But if you're serious about integrating free fuel from the sun into your cooking, the plan below features a solar oven that works beautifully and is also built to last. Plus, you can build it for a fraction of the cost of a purchased solar cooker.
Depending on variables like location, ambient air temperature and the angle of the sun, a solar oven can reach temperatures above boiling (212° F). In ideal conditions, some types can reach 300° or more. This temperature range is high enough that you can safely cook any food, including meat. Cooking times are longer, but because the temperature is lower there's little danger of overcooking, and the food is delicious.
Solar Oven Types
Solar cookers can be made in a wide variety of designs. The main criteria is that they have a reflective side or sides that focus sunlight toward a heat-absorbing (usually black) pot or base.
Made from cardboard and aluminum foil, this solar cooker is still capable of heating food almost to boiling. Variations of this basic design are widely used in poor areas of the world that have abundant sunlight but limited fuel; their use helps preserve dwindling forests.
Solar Oven
There are numerous ways to make a solar cooker—one website devoted to the subject has dozens of photos of different types sent in by people from all around the world—and all of them seem to work reasonably well. We settled on this model mostly because we're carpenters and we like working with wood more than metal. Feel free to modify it as you wish.
The cooker is big enough to hold two medium-size pots. All the pieces are cut from one eight-foot-long 2 × 12 and a sheet of ¾" plywood. The cooker would work just as well with ¼" plywood, but we used ¾" because it made it simpler to screw the corners and edges together. The base is made from 1½"-thick lumber for ease of construction and for the insulation value of the thicker wood, but thinner material would also work.
The foil we used was a type recommended for durability and resistance to UV degradation by an independent research institute. Unfortunately, it was expensive, and if you're just starting out you may want to do a trial run with heavy-duty aluminum foil. Although foil looks a little dull, it actually reflects solar rays almost as well as specially polished mirrors.
Tools and Materials 
• Straightedge
• Circular saw
• Jigsaw or plunge router
• Tape measure
• Drill/driver with bits
• Speed square
• Stapler
• Eye and ear protection
• #8 countersink bit
• ¾" × 4 × 8-ft. BC or better plywood
• 2 × 12 × 8-ft. SPF SolaRefle× foil  or heavy-duty aluminum foil
• 1⅝ and 2½" deck screws
• Clear silicone caulk
• Contact cement, or white glue and brush, optional
• Mid-size black metal pot with glass top
• Wire rack
• ¼ × 17¼ × 17¼" tempered glass
• No-bore glass lid pulls (Rockler item no. 29132)
• ¼ × 2" hanger bolts with large fender washers and wingnuts
Cutting List 
1½ × 11¼ × 19"
1½ × 11¼ × 16"
 ¾ × 19 × 19"   
 ¾ × 10 × 17"
Adjustable Leg
  ¾ × 20 × 33¾"   
 ¾ × 10 × 25¼"
 ¾ × 20 × 31¼"
  ¼ × 17¼ × 17¼" 
Tempered Glass
Sun rays reflect off the foil sides and are concentrated at the base of the cooker, where they are absorbed by the black pot. The glass cover (or clear oven cooking bag) helps hold heat and moisture in the pot. The cooker should face the sun. Raise or lower the box depending on the time of year so that you catch the sun straight on. Shim the wire rack as needed to keep the pot level.