How to make a really hot Solar cooker?

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Until a decade back solar cookers were still in the experiment stages. Over the years the design and technology has evolved and now these ecofriendly solar cookers have definitely reached a stage where you can cook without a lot of hassle. However the solar energy technology is fairly new and still evolving. As the technology improves and solar technology becomes more efficient the market trend towards solar cooking will change. There are different models of solar cookers and other related solar energy products available in the market, but many still have doubts on whether the solar cooker can really make a difference and cook everyday sauces, meat, mac and cheese etc. The reason for the solar cookers not being very popular is due to a variety of reasons, while many are not aware of this technology as a part of everyday use in the kitchen, in colder countries it is only seasonal and also the notion that it is not very efficient contributes to it being not used as much. One will be surprised that a really hot solar cooker can be used to roast, bake, steam, cook as well as preserve food. So if you are energy and environment conscious, who think out of the box, and like experimenting with alternate ways to reduce energy, you should try this emerging technology and make one this summer and test it for yourself.  



When was the first concept of solar cooker developed?

One of the first experiments on a solar cooker or a solar hot box was made by Horace de Saussure in the (1767)19th century. This hotbox is the predecessor for the current solar cookers. Horace de Saussure was a Swiss physicist who came up with a helio-thermometer and explained the solar radiation. The reason there is a difference in the temperature between the mountains and plains, is the density of the atmosphere. According to him the earth gets equal amounts of solar radiation both on mountains and plains but the plains get heated more due to the presence of water vapor and carbon dioxide(density of air is higher on plains) in a higher proportion in the air on plains. In the mountains as the density of air is much lesser the solar heat is not trapped and thus the temperature is cooler. He demonstrated this by using a hot box on the mountain Cramont in the Swiss Alps. The box itself was a wooden box with a glass cover and the outside temperature was only 16ºF while the hotbox recorded 190ºF. A similar temperature was recorded when he put the hotbox on the plains below where the outside temperature was 43ºF. The box could trap heat very effectively that no matter where it was placed it recorded the same temperature of 190ºF. This same principle is used today in solar collectors and solar cookers. The goal is to trap the solar heat so the internal temperature rises high enough to heat the substances inside, be it water or food.  



What are the  3 principles on which an efficient solar cooker is built?

There are three fundamental principles of heat on the basis of which hot solar cooker is built so that the heat loss is minimum and maximum heat is stored and used inside for cooking. These are: 

  • Heat gain: When the visible light in the form of heat energy enters the glass, it gets absorbed and then reflected with the help of materials that are enclosed inside the space. The dark surfaces absorb the energy then convert this energy into heat energy with comparatively longer wave length. Due to longer wavelength this energy now cannot pass out of the glass and is trapped inside, which makes the solar cooker gain heat for cooking.
  • Heat loss: Conduction, radiation and convection are the three fundamental principles of second law of thermodynamics on which the theory of heat loss is based on. According to this principle, heat always moves faster from hot to cold. Similarly, when the heat within the solar box moves from tin foil, cardboard, glass and insulation molecules it transfers heat. But to prevent this heat loss, the bottom of the really hot solar cooker is covered with an absorber plate that is held up from the bottom and small spaces of insulation slow down the heat loss. Loss of heat through radiation is achieved by using glass surface which can trap heat very effectively.
  • Heat storage: With the increase in the density of material, the insulation and heat retention capacity of the solar box increases and it can then hold much more energy. So, more solid insulation material gives the box more capacity to store heat.



How to make a really hot solar cooker?

You can start your contribution to the eco-friendly living by making a really hot solar cooker at home on your own without using expensive material. Check out the steps for making a hot solar cooker below:

  • Get two boxes. One box should be slightly (2 to3 inches) smaller than other so that the smaller one fits comfortably inside the bigger one leaving a bit of space from all the sides
  • Arrange crumples of newspaper at the bottom of the box
  • Now, put the smaller box above this layer of newspapers
  • Fill the gaps on all the sides with newspapers for better insulation
  • Use non-toxic tapes to line up the sides of the smaller box with aluminum foil from inside and fix it tightly
  • Place the black construction paper at the bottom of the smaller box. Black paper is used because it absorbs the heat fast and also helps in retaining the temperature for long period
  • Cut a cardboard with the size 2 inches more than the top of large box. This will serve as a reflector
  • Cover this cardboard cut out with aluminum foil and secure it tightly by using non toxic tape or glue
  • Attach this  reflector to the large box from its outer back side with the help of staple
  • Keep the very hot solar cooker under the sun with the reflector facing the sun rays at a right angle
  • Put the food to be cooked on a glass or plastic plate (a pie plate is good) and place it inside the smaller box
  • Cover the larger box fully by plastic wrap and secure it from all sides with the help of tape



What can you cook with a really hot solar cooker?

You must be wondering as to what you can cook in this really hot solar cooker. You can almost do all the things that a conventional stove will do such as,

  • Baking: You can use it for baking breads, sandwich loaves, yeast breads, sweet dinner rolls and heavy cakes such as fruit cakes and gingerbread
  • For drying food items: Really hot solar cooker can also be used for drying food items. You can use wire rack or solar dryer for putting the food stuff inside the cooker
  • Coffee roasting: To use solar cooker for roasting coffee is the latest idea tried and successfully implemented commercially by two brothers-David and Mike Hartkop for Solar Roast Coffee. Since all the aroma and richness of the coffee beans is trapped inside the really hot solar cooker, powder grounded from these beans is richly flavored
  • Pasteurization: A simple really hot solar cooker can boil water to more than 149 degrees Fahrenheit. This is the temperature at which the infection causing microbes are destroyed. Usually WAPI or wax based water pasteurization indicator is used to check the exact temperature of water. When the water inside the really hot solar cooker goes beyond 149 degrees Fahrenheit, the WAPI melts. This indicates that the water is free of germs and drinkable
  • Canning: Really hot solar cookers are used for canning acidic food stuffs such as tomatoes and pickles. It is important that you first try basic cooking things before trying innovations


Please add your experience with homemade solar cookers  in our comments section as other innovators will learn from your experience.

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