A Solar Oven For Solar Energy Cooking Is The Way To Go

A Solar Oven is a great way to reduce energy consumption almost anywhere in the world where the sun actually strikes the ground for at least a few hours a day.

The technology is as old as history, nothing complicated is required to build your own solar oven. You require a box made of a material that can withstand the internal heat that will be generated. This must be then insulated enough to hold the heat obtained from the sun. A pane of clear glass is needed to cover the top opening. A reflector adds extra area to capture sunlight direct the rays of the sun into the cooking area.

The Advantages Of Using A Solar Oven

  • A great way to cook outdoors without using any other energy.

  • Keeps your kitchen cooler – great advantage in the warmer months

  • You save money on your energy costs

  • You conserve non-renewable resources

  • Sustains high enough temperatures to cook most food where you would use a conventional oven

The Disadvantages Of a Solar Oven

  • Slower than conventional ovens – probably about twice as long to do the same task

  • You cannot apply pin point heat so there can be no searing or sealing of foods

As you can see the advantages of a solar oven far outweigh the disadvantages.

How Does A Solar Oven Work?

The sun delivers even warmth and consistent power to the oven, which means it is ideally suited to cook all sorts of foods – breads, pastries, cakes, meats, vegetables – that need to be baked or evenly heated.

Most are familiar with the concept of how a greenhouse works. Solar ovens work on the principle of the “greenhouse effect”. You have built a small version of what has been happening on earth since it first created an atmosphere. The rays of the sun easily pass through the clear top of the system and bounce off the dark interior surfaces.

When the sun's rays hit the dark surfaces inside the solar oven, they get converted into longer wavelength heat energy. This longer wavelength heat energy is unable to pass back through the glass so it becomes trapped in the container and the ambient internal temperature rises.

The actual cooking is done in a pot placed inside the solar oven. This pot should be as dark as possible, but not made of cast iron or other heavy and dense metal. Although cast iron is an excellent type of material for most cooking in conventional ovens and over open flames, the solar oven will require too much time to bring a cast iron pot to a suitable cooking temperature.

Select a light weight black pot that will easily hold the amount of food you want to cook. Shiny aluminum or bright stainless steel pots are also not good choices. Their exterior surface reflectivity greatly reduces the amount of heat they can transfer to the cooking contents within. Your lightweight black pot will be more likely to absorb the longer heat wavelengths in the oven and transfer them to the food. Those lightweight black speckled pots and pans (Graniteware) are amongst the best for use in solar ovens.

Some people feel that instead of lining the walls in black, they get better results if they use tin foil or some other highly reflective material. The feeling is that it can increase the efficiency of the heat transfer into the actual cooking area instead of going into the walls. You heat up the pot instead of the area around it. To make this work better, though, the bottom is often left black.

How your solar oven actually evolves becomes a matter for your personal experimentation. You should still ensure the base of the walls and the entire interior is painted flat black to absorb and retain as much heat as possible, no matter what other materials you may choose to try. Experimentation with internal reflective materials can be done once the basic unit is finished and tested.

As discussed in the actual construction steps, outlined below, the unit should be made to withstand the upper level of 350°F(176°C). In practice, the internal temperature of the solar oven will rarely get that hot. It can occur when the sun is shining without clouds for an extended period of time. Ordinary operating temperatures seem to be more within the range between 200°F and 250°F(95-120°C). Watch the internal thermometer (see Step 7 below) to see what the average temperatures are for your oven in a variety of conditions.

A solar oven does not cook as quickly as an electric or gas one. Plan on it taking about twice the time to allow the lower temperatures to slow cook the food. It may not be quick, but the results of cooking this way uses just the resources of nature. The best news, especially for the terrible cooks of this world, is that the food you place in the oven will never burn. And once its has been cooked, it can remain in the oven for extended periods to stay warm without being burned or drying out.

How To Build Your Own Solar Oven

It really isn't difficult to build your own solar oven. The actual steps required are outlined below.

Step 1: Find a good box for the project. It can be made from just about anything. Cardboard boxes are a real possibility, I prefer an old aquarium but if you have a metal box that has good dimensions, or even an old wood or plastic box. Something like a discarded portable beer cooler with its insulation already integrated can be a wonderful choice. Always remember, there will be regular heat applied and the structure must be able to withstand these temperatures.

As mentioned, I prefer an old aquarium, the 40 gallon (breeder) is the size I use, 36"(0.9m) L x 18"0.45m) W x 12"(0.3m) H makes an excellent size for a family oven. The rectangular shape makes it easy to find a suitable glass plate as a cover and the material will easily withstand the regular application of heat.

Step 2: Paint the inside of the box. Visit your local hardware or paint store and purchase a non-toxic flat black paint. The inside of the oven needs to be uniformly covered in this paint to ensure that the heat that is transferred inside remains trapped there. The paint concerned needs to be able to be cleaned easily and not be damaged by mild cleansers.

Step 3: Create a seal at the top of the box to allow the cover to be placed easily. In most cases weatherstripping works great as a buffer between the top of the black box and the glass cover. Modern "peel and stick" stripping usually has a glued surface to ensure a strong bond between the top edge of the box and the stripping material. This should be easy to find at your local hardware store. Make sure the box is airtight.

If an aquarium is used, there is often a black plastic frame around the top edge of the tank. This is an automatic surface to seal the glass plate and makes it even easier to implement. To satisfy the requirement that it be air-tight, a bead of silicone can be run around the edges of the glass cover to allow it to seal to the plastic frame when the oven is assembled and in use. DO NOT add the silicone bead around the tank frame, as silicone does not bind well with plastic - it is a much better adhesive for glass.

Step 4: Insulate your box with Styrofoam panels recycled from old fish shipping boxes (check at your local pet store). Alternatively, use left-over sheets from a home renovation. Even wood can help hold in the heat. Cut the panels into properly sized pieces and attach to the external aquarium glass in a number of ways. At the absolute minimum, use the fish box by itself and line it with a material that can be suitably painted and cleaned. The name of the game here is to prevent the heat from conducting away from your container.

If you want a permanent installation you can use the earth as your insulation by burying your box and back-filling.

The heat can be intense within the black box. Make sure whatever insulation material you do choose will not melt in temperatures close to 350°F.

Step 5: Cover your oven usually with a standard piece of clear float glass that covers the entire opening. It needs to be sealed tightly by the weatherstripping or silicone bead mating to the top of your box. You have insulated the sides and bottoms, you don't want any heat to escape out the top.

Step 6: Construct the reflector. Although some heat will enter the oven directly, the majority of the heat trapped is usually reflected into the oven enclosure by a reflector assembly attached to the side of the box and faced to the sun. There are a few choices you can make here:

  • strong cardboard panels
  • plywood
  • acrylic panels
However, the stronger materials are a better choice for protection in strong winds or unexpected storms.

No matter the actual material you choose to make the reflector from, it needs to be covered with highly reflective material. The shiny side of aluminium foil is a good choice Find a glue that can adhere to both the aluminum foil and your backing material. Glue carefully and smooth out any trapped air bubbles.

Once the panels are as reflective as possible, all that is required is to place the reflector onto the sealed oven and the unit will immediately start to heat. You may have to experiment with ways to attach the reflector to the oven body to ensure it will remain in place. One way, when using Styrofoam would be to insert a couple of pegs into the oven insulation material and strap the reflectors to the unit with elastic or even "bungee cords"

Step 7: Use a metal oven thermometer to track the internal temperature of the food, to know when it is safely cooked. Be sure is it kept plainly visible through the glass cover. Removing the top cover will cause a rapid drop in temperature so only remove the top cover when the food has reached the proper temperature and is fully cooked.

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