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Solar Cooker

The solar cooker which cooks almost anything!

In this section we will see how to build a solar cooker, a very simple and inexpensive construction, which can cook any food or boil water, simply with solar energy and without electricity.

The solar cooker exists in the commercial market and it costs around 180 Euros. It will cost us less than 30 Euros!

An electric cooker can be set at 200 degrees Celsius for cooking. The food, however, could be cooked with much less heat, just with twice the time.

In fact, all foods can be cooked at temperatures of about 100 degrees Celsius. The solar cooker temperatures are between 100C to140C, depending on the sunlight.

How can the solar cooker develop such temperatures?

By omitting the details that we will see below, we can say that the solar oven is essentially an insulated box with a glass lid. The solar radiation penetrates the glass and is being converted into heat which is trapped inside the box, constantly raising the temperature.

In about 45 minutes it has reached 100 degrees, which is the boiling point of water. The solar cooker does not need constant sunshine. It only needs the sun to appear for 30 minutes every hour and let there be clouds for the rest of the time.

Furthermore, the solar cooker does not need high ambient temperatures. As long as there is sunshine you can cook even if there is snow and the temperature is 2C. It is reasonable to expect that the months from November till February there will be less sunny days than during the rest of the year.

How to build a solar cooker?

The construction is very easy and the cost of materials does not exceed the 30 Euros. Under other circumstances it might even be less than 5 Euros!

1. Firstly we build two boxes like in the photo. One of the boxes should be slightly smaller than the other so that the little box could fit inside the large, leaving about 3 cm gap between the sides and bottom. This gap will be filled with crumpled pieces of newspaper for insulation.
2. Then, we order a piece of glass with thickness 5 mm, having such dimensions as to cover the entire top of the large external box (like a cap).
3. Cover the inside walls of the small box with aluminium foil to reflect the light which does not reach directly to the pan (photo on right). Beware that the glue we use is non-toxic at high temperatures. On the basis of the internal small box we put an iron plate.
4. Place a strip of insulating foam (like the one we use to insulate the windows) around the upper part of the two boxes that will touch the glass. Warning, make sure that there is no possibility of air leaking out of the little box when you place the glass.
5. Finally, we are going to make a reflector made of wood and aluminium foil, which will reflect into the solar cooker for even greater efficiency. A slight tilt towards the sun increases the efficiency. The dish must have lids and it should be made of dark metal, preferably black. Also, it should not be very big (it should barely be able to contain the food).

If you want an economical and occasional solar cooker, you can use cardboard boxes and as a cup, instead of glass, a transparent plastic sheet for the ovens (you can find it in supermarkets). However the performance and durability of the oven will be much smaller.

The test of the solar cooker

The trial was conducted in April when the outside temperature was about 23 degrees C and sunny. The digital thermometer, as shown in the following photos shows the inside of the cooker to be 97 degrees Celsius! The burger was baked well in about 90 minutes as well as the sausages that followed!

General chunks, potatoes and the legumes want more time, while the thin pieces of meat, pasta (rice, pasta in a little water) and vegetables need considerably less time.