The solar oven is a device used for cooking food using solar radiation as an energy source. It is named so due to its resemblance to conventional ovens, but it is actually a solar cooker belonging to the group of accumulation solar cookers, which is why it is also known as a box solar cooker.
In broad terms, what a solar oven does is transform sunlight into useful heat, which is stored in an insulated interior space in such a way that appropriate temperatures for cooking food can be reached.
Parts of a solar oven
Basic parts of a solar oven
There are many models of solar ovens, but in general they all have the following elements:
- Cooking area: it is a space or box, covered with thermal insulation on the bottom and side walls, where heat accumulates and where food is cooked. * Transparent cover: serves as a lid for the cooking area and is where solar radiation enters. It is generally made of glass. * Absorbing plate: is the element that transforms solar light into heat, using materials that have an optimal balance between their absorption and thermal emission coefficients. * Reflectors: Some models of solar ovens incorporate additional flat reflectors, the purpose of which is to capture more sunlight and consequently increase their heat generation capacity.
Operation of the solar oven
The solar oven is a household appliance that operates on solar energy, its main feature is that it allows cooking food at lower temperatures than conventional methods, which has beneficial effects on the taste and nutritional quality of the dishes.
The operation of a solar oven is based on several physical (optical and thermodynamic) principles, to better understand it, it is convenient to take into account the following concepts:
- Greenhouse effect: is the effect that allows increasing heat gradually and homogeneously inside the solar oven. Solar rays have a wavelength that allows them to pass through the oven's transparent cover without difficulty. Inside, the luminous energy is transformed into thermal energy (heat) by the absorber plate. The heat produced by the plate has a longer wavelength, so it cannot pass through the glass and escape outside. In this way, the heat remains trapped inside, raising the temperature in the oven's cooking area, and this is known as the greenhouse effect.
- Thermal insulation: It is the quality that a solar oven must necessarily have to maintain the heat produced by the greenhouse effect inside. If the oven generates heat and loses it easily through the base and walls due to poor insulation, it is unlikely to reach the necessary temperatures to cook food. In addition, effective thermal insulation allows the equipment to work even if the sun is intermittently covered by clouds since the cooking will continue with the accumulated heat.
The following video was made to explain the operation of the Sun Cook solar oven, the information it contains is useful for better understanding the previous concepts and will allow you to visualize how a solar oven works.
Types of solar ovens
There are commercial solar ovens, artisanal manufacturing, and there are also homemade or self-built solar ovens, which vary in power, design, size, materials, etc., however, all of them generally operate under the principles previously explained.
Commercial solar ovens
There are various models of solar ovens available on the market, which are equipment manufactured with optimized materials and are characterized by their high efficiency. Here I am going to introduce you to two of the most well-known and widely used worldwide:
Solar Oven Sun Cook
Solar oven Sun Cook Premium
The Sun Cook solar oven is an efficient device, designed to operate even with partially cloudy skies. It is made with materials that allow high levels of efficiency and an estimated lifespan of 15 to 20 years.
The Sun Cook has two versions, the Tropical (simple and economical) and the Premium which incorporates an additional external side mirror and a solar clock, allowing to program the operating time and facilitating its proper orientation towards the sun.
It can reach maximum temperatures between 180 and 200 ºC, in addition to preparing conventional recipes, it is very useful for making preserves and dehydrating food. The content published here refers to my experiences with the Sun Cook solar oven, which I have been using regularly for several years.
The Sun Cook solar oven is manufactured in Portugal by SunOK Lda.
Solar Oven Sun Oven
Horno solar Sun Oven
The Sun Oven solar oven is a device with very good performance, its design incorporates a system of foldable reflectors to improve the capture of solar energy and an adjustable rear leg, which allows adjusting its correct inclination according to the sun's height. Under favorable atmospheric conditions, it reaches temperatures between 180 and 200 ºC.
It is one of the oldest commercial solar ovens and is very popular in the North American market, reasons that have led to the appearance of Chinese copies, of low price and dubious quality, which are sold as if they were original in different markets, including Spanish. In Spain, it is difficult to find an original Sun Oven solar oven, as at the European level there is only one authorized distributor based in Germany.
Sun Oven solar ovens are manufactured entirely in the United States of America by Sun Ovens International, Inc.
Homemade and artisanal solar ovens
Within the line of artisanal solar ovens, there is a varied offer of devices in almost every country, including Spain. These are small local companies or individuals who offer construction services for these equipment on demand or from small stocks. As for their characteristics and performance, these are very diverse, as they depend on the design, size, and materials used in their manufacture, so it is difficult to provide exact references.
Finally, there are the so-called homemade solar ovens, which are devices built by the interested parties themselves. In books and especially on the internet, it is easy to find guides, designs, and tutorials that explain how to build them at home using easily accessible materials; even some local institutions often hold workshops for building these types of devices.
Building a very low-cost device at home that serves to prepare food using solar energy is presented as a highly attractive alternative for many people with a desire to protect the environment, maintain a healthier diet, and achieve significant energy savings. However, many of these proposals, when put into practice, do not meet these initial expectations for a variety of reasons, which I explain in detail in the section on how to build a homemade solar oven. Therefore, if you are interested in making your own equipment, I suggest reviewing that information beforehand; it will be useful to avoid mistakes and achieve good results.
Cooking food in the solar oven
Recipes prepared in a solar oven have special characteristics that are hardly achievable through other cooking methods. The foods maintain their natural flavor and it is practically impossible for them to burn. Fruits and vegetables preserve their natural color to a high degree, and meats turn out tender, juicy, and with less volume reduction than when cooked using conventional methods.
The greenhouse effect cooking method of the solar oven allows for a very homogeneous distribution of heat, so high temperatures are not necessary to properly cook food, a feature that helps preserve a higher percentage of nutrients and vitamins.
In a high-performance solar oven, you can prepare the same recipes as in a conventional oven and many dishes that are normally cooked in a kitchen, such as stewing, boiling, braising, and steaming; it is only not suitable for frying, but you can sauté and stir-fry. It is also perfect for making homemade preserves and can also be used as an efficient food dehydrator.
Cooking food in a solar oven is extremely healthy, in addition to better preserving nutrients and vitamins, the absence of aggressive heat sources does not promote the elevation of benzopyrenes levels, which are highly carcinogenic toxins naturally present in some foods.
Temperature in a solar oven
Appropriate cooking temperatures in a solar oven
In the chart on the left, it can be appreciated that at temperatures above 82 ºC (180 ºF) food is cooked, consequently a solar oven will be able to cook if it reaches at least 90 ºC, higher temperatures allow cooking faster, in larger quantities, or achieving that the food browns or acquires certain characteristics required by a particular recipe.
A solar oven must be able to reach a working temperature that ensures the cooking of food (above 90 ºC) and do so in a reasonable time for practical purposes. In general, solar ovens operate in the temperature range between 90 ºC and 165 ºC.
The maximum temperature that a solar oven can reach depends first on its efficiency and second on the area and weather conditions in which it operates.
Solar Oven Efficiency
To function, a solar oven receives a certain amount of energy from the sun and transforms it into heat useful for cooking food; however, this transformation is not total, a certain percentage of that received energy is lost, this is normal and the concept is applicable to any machine or device created by man. The greater the utilization (or the lower the loss) of energy, it is said that a device has higher efficiency.
Not all solar ovens are the same, their efficiency is directly linked to the optimization of their design and the quality of the materials used in their manufacture. The temperature that a solar oven can reach under certain working conditions is directly related to the amount of solar energy it receives and its efficiency.
Working conditions of the solar oven
In addition to the characteristics of the solar oven itself, there are external factors that condition the temperatures that can be reached inside, such as:
The temperature in a solar oven depends on its efficiency and the environment in which it operates.
- The geographical location where the solar oven operates conditions the temperature, this is due to the effect that latitude has on the incidence of solar rays. The closer to the terrestrial equator (latitude 0º), the higher temperatures can be generated; for example, if two solar ovens of the same model work under similar weather conditions, one in Madrid and the other in Santa Cruz de Tenerife, the one located in the Canary Islands will reach a slightly higher temperature.
- Atmospheric conditions are obviously decisive, the highest temperatures will be reached on clear, sunny days, without cloud cover, with minimal pollution levels and low humidity percentages. The aforementioned factors determine the level of available solar energy and consequently the power that the solar oven can develop.
- The time of year and the time when a solar oven is used also influence, in summer the sun is higher and its angle of incidence on the earth's surface allows for capturing more energy, which will achieve higher temperatures than those obtained in winter. Similarly, during the central hours of the day, the sun's height is greater and therefore the availability of energy is higher, compared to the energy available in the early morning and at sunset.
Contrary to what might be thought, the ambient temperature is not a factor that seriously affects the performance of a solar oven. On a winter day with sun, clear sky, and low humidity, higher temperatures can be achieved than on a sunny summer day with high ambient humidity.
Cooking times in the solar oven
The cooking time of food in a solar oven will depend on the working temperature of the equipment we are using. Not all solar ovens are the same, nor do they have the same thermal power; there are devices that barely reach temperatures around 90 ºC where food will take many hours to cook, and there are also those high-efficiency equipment capable of reaching higher temperatures where food will take a completely reasonable time to cook.
In addition to the working temperature of the solar oven, which depends on the power of the equipment and the characteristics of the solar radiation at the time of cooking, there are also other factors that affect the cooking time of food, here are some recommendations:
Some ways to improve cooking times in the solar oven
- The type, quantity, and size of the foods being cooked influence the cooking time. Recipes with less water will cook faster, and similarly, foods cut into pieces will take less time than if cooked whole.
- Reorienting the solar oven frequently to follow the sun's movement across the horizon helps speed up cooking, ensuring the maximum working temperature throughout the process.
- While any type of pot or tray can be used in a solar oven, thin-walled, matte black metal containers are most suitable for quick cooking of foods.
- Try to use pots and pans that match the quantity of the preparation and always use them with the lid on whenever possible.
- Reduce the number of times the oven cover is opened; each time this is done, there is a drop in the interior temperature, consequently prolonging the cooking time.
- In some preparations, using roasting bags is highly recommended as it prevents steam formation and concentrates heat on the foods.
By way of reference and based on experiences with the Sun Cook solar oven, cooking times on clear summer days are similar to those used in a conventional oven. In winter, cooking takes a little longer, depending on the recipe, and in extreme cases, that time can double.
Recipes for solar oven
To cook in a solar oven, no special recipes are necessary, although in some preparations it is advisable to make some variations or adaptations if you want to optimize the cooking time or achieve a special finish.
Cooking conventional recipes in a solar oven always poses a challenge, from which most of the time one emerges well and comforted by the extraordinary results. Personal experience sets certain guidelines, and some useful suggestions are:
Some recipes prepared in Sun Cook solar oven
- Reduce, as much as possible, the amount of water or liquids from the original recipe.
- Cut the food into uniform and not too large pieces.
- Use suitable cooking containers and preferably with a lid.
- To achieve a more golden finish in the recipe, use a black metal lid.
- If you want to better preserve the natural color of the food, use a glass lid.
- Do not use aluminum foil, neither as a base nor to wrap the food, it is toxic and significantly increases the cooking time.
- The temperatures indicated in traditional recipes are designed for conventional ovens, they do not necessarily apply to a solar oven.
- In many preparations, you can place the food in a cold oven. For bread and cakes, preheating is recommended, but the temperature control done in conventional methods is not necessary; heating the oven 30 minutes before starting the cooking is sufficiently valid.
- The only processes that require careful temperature control are canning sterilization and food dehydration, where the use of a thermometer is essential.
Advantages and disadvantages of a solar oven
The use of a solar oven offers many benefits derived from its way of operating and from using a completely clean and free source of energy.
The practical utility of a solar oven at a household scale depends on its performance. An equipment with acceptable efficiency allows preparing food for a family, in winter or summer, similarly or even with better results than using conventional cooking methods.
Advantages of the solar oven
There are many benefits that a solar oven offers, there are advantages in terms of gastronomy, environment, safety, and economics.
- Nutrients and vitamins of the food are better preserved.
- Fruits and vegetables maintain their color and natural flavor.
- Meats are tender, juicy, and with less volume reduction.
- Several cooking containers can be used simultaneously.
- In addition to preparing recipes, it can be used for pasteurizing, sterilizing preserves, and dehydrating food.
- Foods are hardly burned, even if the cooking time is exceeded, which is beneficial for health and undoubtedly an advantage from a practical point of view.
- Its use does not produce any type of associated pollution. There are no fumes, no noise, and no contaminating emissions are generated into the atmosphere. * The experience of cooking in open spaces and outdoors promotes social relationships and is very psychologically healthy.
- It is impossible for them to cause a fire or explosion
- In the event of a natural disaster, it allows for a means to prepare hot food that works without the need for fuel or electricity.
- A solar oven can operate unattended, and its exterior parts are completely safe to touch, with high temperatures only inside.
- Allows for significant cost savings, it is a device that always uses kW-h at zero cost. * The price of a solar oven is quickly recouped through energy savings.
Disadvantages of the solar oven
- They need the presence of sun and certain atmospheric conditions to function, which makes it impossible to use them at night or on very cloudy or rainy days. * For their use in homes, houses must have a sunny area (garden, terrace, patio, etc.) facing south and free of shadows, which sometimes is a limiting factor. * They do not generate temperatures high enough for frying. * In unfavorable weather conditions or in some preparations, cooking times may be somewhat longer compared to traditional methods.
Solar cookers, despite their many advantages, like any machine or artifact, also have disadvantages, therefore they do not constitute an ideal and perfect solution, however in the environment of economic, energy, and environmental crisis that we live in, it is an extremely interesting alternative for cooking in a healthy, economical, and ecological way, especially if we consider the enormous potential of hours of sunshine that Spain has thanks to its privileged geographical location.
In this section, a summary has been presented on the operation and most important features of solar ovens in general. I hope it has been useful to you and I invite you to visit the other sections of the website, where information on more specific aspects, recipes, instructions for making preserves and dehydrated foods, tips, and many other topics related to the practical use of the solar oven will be published.