Gardening

Cooking with the sun? Discover everything about solar cooking

In developing countries, their population (around two million people) uses the burning of firewood or cattle excrement to obtain the energy necessary to cook their food, since they do not have access to more modern forms of energy , for structural or economic reasons, such as electricity or fuels from oil or gas refining.

As collateral damage to this practice, around two million women and children die as a result of respiratory diseases derived from inhaling the smoke generated.

It is estimated that half of the planet’s wood is burned for these purposes, which translates into deforestation, erosion, desertification, increased CO2 emissions and the greenhouse effect, to the detriment of biodiversity.

For the reasons stated, it is evident that it is necessary to use alternative energy sources, economical, friendly to the environment and that preserve the ecological balance.

Among the available options are solar, wind (wind) and geothermal energy, the Sun being the most feasible for domestic use because it is free, abundant, non-polluting (without the generation of CO2 or radioactive waste), available daily, does not require be transported or stored and can be converted into caloric energy to be used to cook and bake food by using the Solar Cooker.

There are regions on the planet that are very favorable for the use of solar cooking, such as Asia, Africa and Latin America, since the best areas are those between latitudes of 40 ° and the equator.

However, the use of solar cookers should be encouraged in more developed countries as a way to protect natural resources, maintain biodiversity, combat climate change and favor the ecological balance of the planet.

 

What is a solar cooker?

A solar cooker is a basic piece of equipment that uses solar radiation and transforms it into thermal energy, thus allowing food to be cooked, heating it once it is cooked and eliminating possible microorganisms present in the food. The cooking of a large part of the food is necessary to facilitate its digestion and for it to be assimilated and used properly by the body, especially most carbohydrates and proteins, such as meats and legumes.

It is a simple, ecological (does not pollute) and economical way of cooking, since once the solar cooker is purchased, there are no extra expenses of any kind, except its periodic maintenance.

 

TYPES OF SOLAR KITCHEN

Direct solar cookers

The food is heated directly inside. In turn, these can be accumulation or concentration.

  1. Accumulation kitchens (great insulation):

They work on the principle of the accumulation of heat or greenhouse effect. Solar radiant energy passes through a transparent material such as glass or plastic and is stored inside a thermally insulated space everywhere.

The side walls must reflect this radiation so that the saucepan receives as much heat as possible. The pan and the bottom wall where it rests are usually black in order to increase the absorption of radiation. An insulator is placed between the internal and external walls to withstand the temperatures reached, in addition to minimizing heat loss. They are also often called solar ovens.

When the walls are heated and radiated towards the food, temperatures between 90º and 120 ° C can be reached progressively, which facilitates slow cooking without burning the food.

The best pots for cooking in this type of solar cooker are those made of aluminum or copper due to the high thermal conductivity of these metals, preferably with a black outer surface, to reduce cooking time.

The advantages of this type of kitchen are: they are oriented to the Sun every one to two hours, they are inexpensive, you can cook on cloudy days because they capture both direct and diffuse radiation. However, due to the heat concentrated inside and because they are closed, it is difficult to stir the food or add ingredients to the pot once it is placed inside the solar cooker.

  1. Concentration kitchens

They work by concentrating the sun’s rays towards the container with the food to be cooked. This is achieved through a structure, generally parabolic in shape, made of reflective material that concentrates solar radiation.

This kind of solar cooking allows to reach temperatures higher than those of solar ovens, about 200 ° C inside the pot on sunny days, which allows operations such as: steaming, boiling, braising, roasting and frying.

Their disadvantages are: they must face the Sun every ten or fifteen minutes, due to the high heat they generate, they need constant attention so that food does not burn, they must be protected from the wind and they do not allow cooking on cloudy days since radiation is diffuse and cannot concentrate.

Below we present a comparative table between both types of direct kitchens:

Use of solar accumulation and concentration cookers
Characteristics Accumulation kitchen  Concentration kitchen
Need for reorientation Half high
Ease of handling Simple Regular
Stability against wind Good Short
Achievable temperatures Regular High
Cooking speed Short high
Need for vigilance Reduced Elevated
Risk of fire Null Possible
Price Under Highest
Maintenance Very small Regular
Easy access pots Reduced Easy
Auto construction Easy More complicated
Cleaning the pots Simple Normal
Ease of storage Good Regular
Allows frying and / or roasting Not Yes

Source: GARCIA, J.

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Indirect solar cookers

As the name implies, the heat energy in these stoves comes from an external source, a heat collector, whose energy is transported and pumped through a closed circuit to the kitchen using a heat-carrying liquid. Its construction is more complex, being less popular.

Examples of these collectors are vacuum, parabolic-trough, flat or paraboloid of revolution.

This type of kitchen is more expensive, but they allow you to cook indoors.

solar kitchen

 

Components of a solar cooker

Solar cookers can be built from a wide range of materials, such as: cardboard, wood, plywood, masonry, bamboo, cement, bricks, stones, fiberglass, woven reeds, cane, plastic, papier-mâché , clay, trampled dirt, metals, tree bark, or other materials.

The components of a solar cooker are:

A collector : that absorbs radiant energy and transforms it into thermal energy, usually black in color. In accumulation kitchens this function is fulfilled by a metallic plate (galvanized iron, aluminum, steel or copper) painted matt black, located on the floor of the solar cooker in order to absorb direct radiation as much as possible. In concentration kitchens, the collector is of the parabolic type and is made of reflective materials, such as mirrors, aluminum foil or stainless steel. The solar radiation that falls on the reflecting surface is reflected concentrating the rays on the pot.

Absorbing surfaces: surfaces covered with materials that absorb incident solar radiation and emit very little of the captured energy, which significantly reduces radiation losses, improving the efficiency of the solar cooker. The most common materials used are metals such as black nickel, black chrome, and black zinc, oxides such as copper oxide, cobalt oxide, iron oxide, and tungsten oxide, and materials such as brass and anodized aluminum.

Transparent cover : to allow the passage of incident solar radiation into the kitchen. Glass, acrylic, and other plastics are some of the most widely used materials. To increase the gain and decrease the loss of heat energy, some models of solar cookers use double or triple covers, but this increases the cost and makes them heavy.

Thermal insulators : reduce the transfer of heat by conduction from the interior of the kitchen to the outside, in order to achieve temperatures high enough for cooking. In low-cost kitchens, wood, paper and cardboard are used as thermal insulators. Other insulating materials include: aluminum foil, feathers, rock wool, cellulose, rice husks, wool, straw, and newspapers. Fiberglass and expanded plastics are not recommended due to their environmental impact and high cost.

It is important that the insulating materials surround the inside of the solar box cavity where you cook, on all sides, except for the transparent cover. The less heat loss there is, the higher the cooking temperatures .

Vapor barrier: This barrier will prevent water damage to kitchen materials, both insulating and structural, due to the migration of water vapor, coming from the food that is being cooked, to the walls and the bottom of the kitchen. kitchen.

Reflective materials : used to reach higher temperatures inside the solar cooker. Reflective surfaces allow sunlight to be concentrated. Among the most used materials are aluminum and silver.

 

Where to locate a solar cooker?

The solar cooker must be located in a place where it receives the highest incidence of solar rays throughout the day, without the possibility of receiving shade due to the presence of obstacles such as walls, ceilings, vegetation, solid structures, etc. Some possibilities include land or spaces attached to the house, or on the roof of the house if the house does not have outdoor spaces.

 

What else to consider with solar cookers

We must take into account that cooking with solar cookers is slower, especially with accumulation cookers (solar ovens).

Cooking time is also influenced by the material and thickness of the pot, the amount and type of food to be cooked, and the water content.

As long as there is sufficient incidence of the sun’s rays, the external ambient temperature does not influence the cooking of the food.

Generally, food achieves its cooking between 80º and 100ºC, however, it only needs to reach 74ºC to eliminate most of the pathogenic germs that cause diseases.

In the case of accumulation cookers:

  • Keep the transparent cover in good condition to allow the entry of solar rays, the thermal insulators to prevent heat leakage and the reflective surfaces to increase the internal temperature.
  • Once cooking has started, avoid opening it unnecessarily as heat energy would be lost, lowering the temperature and lengthening the cooking time.
  • Reposition it towards the sun every 1 to 2 hours
  • Works on cloudy days

In the case of concentration cookers:

  • Maintain the concentrating surface of solar energy, usually a satellite dish, in good condition.
  • Reposition it in the Sun very frequently since the maintenance of the cooking temperature depends on it.
  • It is important to use black pots to absorb the concentrated energy more effectively.
  • Since higher temperatures are reached, it is necessary to monitor cooking to prevent food from burning.
  • Can’t cook on cloudy days

 

Advantages and disadvantages of solar cooking

ADVANTAGE

  • Low installation cost
  • Simple to use
  • Economical, do not require any fuel
  • Easy to clean and maintain
  • Higher nutritional quality of food due to slow cooking and lower temperatures used
  • Ecological and friendly with the environment, they do not generate smoke or carbon dioxide.
  • Since they do not generate smoke, they prevent respiratory diseases and deaths from this cause
  • Greater security. They do not cause fires
  • Possibility of homemade and artisanal manufacturing
  • They can be used to make water drinkable for free, using heat
  • Benefits countries and regions where energy resources are scarce and / or expensive

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DISADVANTAGES

  • Since it needs the Sun for its operation, it is not possible to cook at night or when the weather conditions are adverse.
  • It takes longer to cook
  • If the room temperature is very cold, it is uncomfortable to cook outdoors
  • They must be reoriented several times a day to maintain their efficiency. They work best in the noon hours
  • They are not suitable in high latitude regions, far from the equator
  • More complex to implement in cities where people live in buildings without external areas

Consulted bibliography:

Ultra-low consumption solar cooker

University Carlos III of Madrid. Department of. Thermal and Fluid Engineering. End of Degree Projects Higher Polytechnic School [2413] 2016-03

Cooking with the Sun every day of the year

Eduardo A. Rincón Mejía ‘Faculty of Engineering, Autonomous University of Mexico City UAEM. December 2001

The solar cooker. A system of direct use of solar energy to cook food together with other applications

Bibliographic journal of geography and social sciences

University of Barcelona


ISSN: 1138-9796.


Vol. VII, No. 376, May 25, 2002

ALTERNATIVE ENERGY “Replacement of the fossil fuel cooker with a solar energy cooker”

Industrial Design Seminar, Production Process Seminar, November 2007

UNIVERSIDAD DE CHILE, Faculty of Architecture & Urbanism, School of Design, Industrial Design Career

The sun, solar cooking and solidarity: a very tasty recipe

Eureka Magazine on Science Teaching and Dissemination, Vol 7, No 2, 2010

New field experiences with solar cookers

Advances in Renewable Energies and the Environment (AVERMA) → Volume 04, Year 2000

 

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