In parts of the world with a reliable energy infrastructure, solar cooking is more of a pastime than it is a necessity. But that could change in places like California, where extended power outages to prevent wildfires threaten to become the new normal. The ability to cook food and heat water is not a given in many rural areas of the world, however, and for people who live there, solar ovens can be a lifesaver.

Solar Cookers International, an international advocacy group, states that three in seven people in the world lack fuel for cooking. These people are also unlikely to have sanitary water sources, and they often lack reliable sterilization methods, which exacerbates the risk of disease and infection. For them, and for people in emergency situations everywhere, solar ovens provide more than one essential function.

Construction of a Solar Cooker

Every solar cooker incorporates a reflective surface that focuses the sun's energy on the item being cooked. The original solar cooker, which was devised by Swiss physicist Horace de Saussure in 1767, was essentially a glass box. A modified version incorporating mirrors was able to cook meat in one hour, and a well-insulated model provided cooked food for astronomer William Herschel as he traveled through South Africa in 1830.

Today, the hot box just is one of four available types solar cooker. The other three are either more portable or generate more intense heat, but the hot box remains one of the most popular, if not the most popular type. All types have their advantages and disadvantages:

The Panel Cooker: The lightest, most portable and most affordable cooker, this type of oven consists of an array of reflective panels that usually fold up for easy transport. When deployed, the panels focus sunlight on a central cooking area and can cook a meal in a matter of hours. Its main weakness is its lack of insulation.

The Parabolic Cooker: Like a panel cooker, a parabolic cooker has reflective panels, but they are curved to focus sunlight more intensely on the cooking area. This cooker also lacks insulation, but it makes up for it by generating enough heat to actually fry food.

The GoSun Stove: This relatively new innovation consists of a vacuum tube which holds the items to be cooked. The tube allows sunlight to penetrate, and the vacuum acts as an insulator to hold the heat inside. It can cook a meal for eight in less than an hour and works on windy and partially cloudy days and even in freezing weather.

The Hot Box: The standard solar oven, and the one you would probably make if you were involved in a solar cooker project, is an insulated box with a glass cover and a reflective panel that focuses light on the cooking area. Higher-end models have more efficient insulation and more panels. On the whole, the hot box costs just a little more than a panel cooker, and because it's insulated, it has a wider range of use, although it is less portable.

Cooked Food Is Safer to Eat

Cooking food makes it taste better, but that isn't the most important reason for doing it. Heating your food to a temperature sufficiently high to kills micro-organisms that can cause disease makes it safer to eat. The importance of a solar cooker is that it can generate the heat sufficient for doing this with no fuel source other than the sun's energy, which is vital in places where wood and petroleum are in short supply.

Even though taste is a secondary consideration, it's still an important one, and food from a solar oven, particularly a hot box or GoSun cooker, often tastes better than food from a conventional one. That's because the juices from the food are retained inside the oven and recirculate into the food rather than being dissipated into the atmosphere.

Importance of Solar Cookers for Purifying Water

Many parts of the world in which fuel is scarce have high temperatures and humidity, which are ideal conditions for micro-organisms and pathogens that pollute the waterways. Even water drawn from wells quickly becomes contaminated in such conditions, and diseases such as typhoid and cholera pose serious health hazards.

The Solar Cookers International Network noted that pasteurizing water in a solar cooker before consumption by raising the temperature to 151 degrees Fahrenheit (66 degrees Celsius) is an effective way to purify it (as opposed to heating to 212 F/100 C as you would in a kettle on a stove), and every type of solar oven can achieve sufficient temperatures for this under the right conditions.

Solar stills that collect water vapor from boiling water, condense it and deposit it in clean containers are more commonly used for this purpose than cookers, though. Even simpler, the Swiss Federal Institute of Aquatic Sciences and Technology recommends SODIS, a method of water purification that involves filling clean, clear PET bottles with water and leaving them in full sun for six hours.

In parts of the world where contaminated water is a major cause of disease, authorities recommend boiling it for at least 10 minutes prior to drinking it. The cost of fuel to do this represents a significant portion of the daily income for people in these areas, but the sun's energy is free. Only a small amount of water can be purified at one time in a conventional cooker, but researchers have developed deep-dish box cookers that can process up to 3 gallons on a sunny day.

Sterilizing Medical Equipment With the Sun

In countries where clean water is scarce, infections that develop as a result of improperly sterilized medical equipment are common. Chemical disinfectants, such as iodine, are seldom available, and fuel for boiling water is expensive. In such places, solar ovens provide a cheap and available alternative to wood and petroleum for heating water.

The preferred device for sterilizing medical equipment is the autoclave, which generates steam and feeds it into a pressurized container. A solar-powered device called a solarclave uses the sun's energy to generate the steam through the use of metal and carbon nanoparticles scattered in a aqueous solution. These particles absorb heat very quickly and transfer it to the water, which vaporizes even on cool days to create a steam bath that sterilizes equipment in about 30 minutes.

Solar Cookers Keep the Air Clean

One of the big problems with using wood and petroleum to heat water is that wood fires release harmful gases and particulate matter into the air, and people have to breathe that air. This is especially dangerous when the fire is in inside a house with an inadequate chimney and poor ventilation, as happens in many rural areas. The World Health Organization states that 4 million people die each year from illnesses associated with indoor cooking.