Solar Cooker

What is a solar cooker?

A solar cooker is a device which uses the energy of direct sunlight to heat, cook or pasteurise drink. Many solar cookers currently in use are relatively inexpensive, low-tech devices, although some are as powerful or as expensive as traditional stoves, and advanced, large-scale solar cookers can cook for hundreds of people. Because they use no fuel and cost nothing to operate, many nonprofit organizations are promoting their use worldwide in order to help reduce fuel costs (especially where monetary reciprocity is low) and air pollution, and to slow down the deforestation and desertification caused by gathering firewood for cooking. Solar cooking is a form of outdoor cooking and is often used in situations where minimal fuel consumption is important, or the danger of accidental fires is high, and the health and environmental consequences of alternatives are severe.

How does it work?

1) Concentrating sunlight: A mirrored surface with high specular reflectivity is used to concentrate light from the sun on to a small cooking area. Depending on the geometry of the surface, sunlight can be concentrated by several orders of magnitude producing temperatures high enough to melt salt and smelt metal. For most household solar cooking applications, such high temperatures are not really required. Solar cooking products, thus, are typically designed to achieve temperatures of 150 °F (65 °C) (baking temperatures) to 750 °F (400 °C) (grilling/searing temperatures) on a sunny day.

2) Converting light energy to heat energy: Solar cookers concentrate sunlight onto a receiver such as a cooking pan. The interaction between the light energy and the receiver material converts light to heat. This conversion is maximized by using materials that conduct and retain heat. Pots and pans used on solar cookers should be matte black in color to maximize the absorption.

Advantages

  • High-performance parabolic solar cookers can attain temperatures above 290 °C (550 °F). They can be used to grill meats, stir-fry vegetables, make soup, bake bread, and boil water in minutes.
  • Conventional solar box cookers attain temperatures up to 165 °C (325 °F). They can sterilize water or prepare most foods that can be made in a conventional oven or stove, including bread, vegetables and meat over a period of hours.
  • Solar cookers use no fuel. This saves cost as well as reducing environmental damage caused by fuel use. Since 2.5 billion people cook on open fires using biomass fuels, solar cookers could have large economic and environmental benefits by reducing deforestation.
  • When solar cookers are used outside, they do not contribute inside heat, potentially saving fuel costs for cooling as well. Any type of cooking may evaporate grease, oil, and other material into the air, hence there may be less cleanup.

Models

Box cooker

A box cooker has a transparent glass or plastic top, and it may have additional reflectors to concentrate sunlight into the box. The top can usually be removed to allow dark pots containing food to be placed inside. One or more reflectors of shiny metal or foil-lined material may be positioned to bounce extra light into the interior of the oven chamber. Cooking containers and the inside bottom of the cooker should be dark-colored or black. Inside walls should be reflective to reduce radiative heat loss and bounce the light towards the pots and the dark bottom, which is in contact with the pots. The box should have insulated sides. Thermal insulation for the solar box cooker must be able to withstand temperatures up to 150 °C (300 °F) without melting or out-gassing.

Parabolic cooker

Parabolic solar cookers concentrate sunlight to a single point. When this point is focused on the bottom of a pot, it can heat the pot quickly to very high temperatures which can often be comparable with the temperatures achieved in gas and charcoal grills. These types of solar cookers are widely used in several regions of the world, most notably in China and India where hundreds of thousands of families currently use parabolic solar cookers for preparing food and heating water. Some parabolic solar cooker projects in China abate between 1-4 tons of carbon dioxide per year and receive carbon credits through the Clean Development Mechanism and gold standard. ‘

Panel cooker

Solar panel cooker designs incorporate elements of box and parabolic cookers. They often have a large reflector area and the cook pot has some form of enclosure to retain heat. Panel cookers are capable of cooking up to approximately 140 °C (284 °F). They are the easiest style to make and relatively inexpensive to buy. Solar Cookers International’s ”CooKit” is the most widely used panel cooker. Panel cookers, due to their ease of construction and low-cost materials, are the simplest solar cookers to build and the most common. Tens of thousands of these are in use in refugee camps around the world.

Benefits with solar cooking

Environmental

  • We are all dependent on the earth’s limited resources of fossil fuels. And the dwindling forests are being depleted for firewood. Cooking with the sun reduces the dependence on these resources.
  • Burning wood, charcoal, fossil fuels, and other types of fuel contribute to the ever increasing global air pollution. Because there is no fire and no flames, there is no air pollution. Because there is no fire and no flame, solar cookers can be used in “no burn” areas and on “no burn” days. So it is perfect for camping in areas with fire restrictions.
  • Because solar cookers use the sun and you use less fuel, there is less garbage to deal with. There are fewer bottles of butane to carry to a campsite, and fewer bottles to carry out of a campsite. And, of course, fewer empty butane bottles in the landfill. Large solar ovens have been built on top of Mt. Everest for this same reason – fewer bottles of fuel to carry up and down the mountain.

Health

  • The use of solar ovens not only reduces air pollution outside, it reduces air pollution inside as well. Smoke from cooking fires irritates and injures the lungs and eyes. With fewer open cooking fires and less smoke, the health of women and children around the globe is improved.
  • Whether it be in a village hut or on a suburban patio, open cooking fires and hot barbeque grills present a danger to everyone, but especially to children.  Using a solar oven, with no open flames, prevents burns and is safe for children to play around.
  • In developing countries, women and children must leave the safety of the village every day, walking further and further distances, to gather a days worth of firewood or dung for the cooking fires, exposing them to dangerous animals and dangerous people. A solar oven keeps them safely in the village, out of harms way.
  • Unsafe water is the cause of 80% of all illnesses and deaths in developing countries.  Millions of people die every year from those diseases. Water can easily be pasteurized in a solar oven, because water does not need to be boiled to be safe. Heating water to just 150 degrees (65 degrees C) pasteurizes it and makes it safe for drinking. Food can be pasteurized at 180 degrees (82 degrees C). A simple, inexpensive device known as a WAPI (WAter Pasteurization Indicator) can be used to determine when the water is safe.
  • When camping, a solar oven can be used to heat water from clean water sources to be used for doing dishes or bathing, as well as drinking and cooking. Again, a WAPI can be used to determine that the water is safe.
  • Solar ovens can be used to sterilize dishes and medical equipment.