A solar oven

by Victoria Aguilera Velazco

Make it yourself (Issue IV/2021)

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Ein Solarofen Modell Ulog. Foto: Victoria Aguilera Velazco


A solar oven uses thermal solar energy to cook food. Like in a greenhouse, the sun's rays are absorbed and converted into heat. However, the temperatures reached are lower than with classic ovens, 120 to 140 degrees Celsius, and sometimes 150 degrees Celsius if the sun is strong. So you have to allow a little more time for cooking. Depending on the food, preparation takes twenty to thirty minutes longer.

I myself have been cooking for a long time, exploring different ways of preparing food. I studied renewable energy in Oaxaca in the south of Mexico and then I was looking for possible applications for solar energy. I met people who were already working with solar cookers, and that's how I came to the project “Cocina solar México” (Solar Kitchen Mexico) almost ten years ago, which promotes solar cooking in some communities in the state of Oaxaca. In the meantime, I have founded my own company - La Sazón del Sol (The Spice of the Sun). There we use different solar cooking techniques to produce food - some of them already existed, others we developed. For me personally, it's about showing how versatile solar cooking can be.

“A reflector with an aluminium foil attached to the oven directs the solar radiation into the cooking trough”

The solar oven I am presenting here is similar to the Ulog model developed in Switzerland. It consists of two boxes, one inside the other. The outer box can be made of wood, plywood or cardboard. For the inner box, you can use aluminium, sheet metal or cardboard - aluminium and copper transport the heat best. The inner box is painted with matt black paint. An insulating layer of wool, insulating foam or glass wool is placed between the two boxes to reduce heat loss. The stove is closed by a window with double glazing. An air space between the two panes of about two centimetres also prevents heat from escaping, and a reflector with an aluminium foil attached to the stove directs solar radiation into the cooking well. The reflector is aligned according to the position of the sun.

We offer workshops for organisations and rural communities to learn how to build and use solar cookers. In the beginning, we showed how to prepare simple traditional Mexican dishes in the courses. Then I thought if there were more recipes, people would be more likely to use the solar ovens in their everyday lives. So over time, more and more dishes were added. Stews and sauces can be slow cooked in solar ovens, but also bread, biscuits and cakes can be baked. Fruit can be dried in them. And with the seeds roasted in the oven we make granola for muesli. You can also use the ovens to preserve food.

“Vegetables go into the oven without any water. Even potatoes and eggs can be cooked without adding water”

The ovens have the great advantage that they do not need electric energy, gas or firewood, only sunshine. And you don't have to be there all the time while cooking. At most, you stir once in between. With bread or cakes, you don't have to do anything else. Slow cooking also preserves many nutrients, as well as flavour and colour. For sauces, you need to add less liquid. Vegetables go into the oven without any water. Even potatoes and eggs can be cooked without adding water. You only have to be careful when you take the pots out of the oven, as they can get quite hot.

To build a large solar cooker, we need two whole days. Simpler models made of cardboard and aluminium foil just take a couple of hours. Most recently, we assembled 35 solar ovens in San Dionisio del Mar, a small community in the south of the Tehuantepec Isthmus. By now, through our workshops, there should be around three hundred ovens in the state of Oaxaca. And not only in rural areas, we have also given courses in the capital Oaxaca. To set up a solar oven, all you need is a small garden.

When it is in operation, the oven does not emit any emissions, but the individual materials needed for its manufacture, such as aluminium, consume a lot of energy during production. That's why we use environmentally friendly paints and certified wood.

As told to Timo Berger


 



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