The photovoltaic panel isn’t the only hot technology under the sun. The solar cooker, a fuel-free alternative to the traditional stove, is another invention that can harness solar energy. While not as sophisticated as its photovoltaic cousin, the humble solar cooker is an important tool in sustainable development. It heats food by concentrating light onto a black pot using aluminum foil. Unlike a photovoltaic cell, a solar cooker requires neither rare earth metals nor integrated circuits. Its elegant simplicity makes it incredibly cheap to build. In fact, hand-made solar cookers are often made of ordinary junk lying around the house. But don’t let its modest, low-cost practicality fool you: solar cookers can reduce carbon emissions, protect forests, and enrich the poor.
To understand the value of the solar cooker, it’s important to grasp the drawbacks of a conventional stove. Every stove, whether it burns natural gas or firewood, requires fuel. Even an electric stove burns fuel, since electricity from the power grid comes from coal power plants. When fuel is burned, it generates carbon dioxide gas, which aggravates global warming. What’s worse, fuel often doesn’t burn cleanly. Incomplete combustion leads to smoke, which is made of particles that can irritate the lungs and eventually cause disease. The effects are worst for poor people cooking over fires with poor ventilation.
Overuse of cooking fuel leads to scarcity. Burning too much coal and natural gas depletes limited reserves, while burning too much firewood leads to deforestation. Fuel is also expensive, with the heaviest burden falling on the world’s ultra-poor. As much as half of a family’s income may be wasted on firewood alone. That income could have otherwise been invested in nutritious food, clean water, immunizations, and education. The world’s poor don’t have much money to burn.
The solar cooker provides an attractive solution. It runs entirely on clean, renewable solar energy. It produces no carbon emissions, requires no fuel, and saves one hundred percent of operating costs. Unlike with modern stoves, solar cookers can be built with common household items like cardboard, aluminum foil, glue, and a pair of scissors. A do-it-yourself version can be assembled in under an hour.
Solar cookers are based on simple principles. Light rays from the sun are not strong enough by themselves to cook food. Rays collected from a broad region, however, can be focused onto a small pot using reflective metal sheets to increase the delivered power. Pigments on a black pot absorb these light rays effectively to convert them into heat. On a hot day, a solar cooker can reach temperatures up to 165°C (330°F) — hot enough to boil, cook, and bake food.
The two essential components of a solar cooker are the pot and the reflective sheet metal. The ideal pot is black, since dark pigments work best for converting light rays into heat. White pots, or pots with shiny metal surfaces, do not work well because they reflect incoming light. The second component, the reflective sheet metal, is often aluminum foil because foil is cheap and widely available. The foil is glued onto a scaffold (often cardboard, sometimes an umbrella) so that it can help concentrate light rays onto the pot. Variations in design center around the arrangement of aluminum foil and the type of insulation the solar cooker uses.
Two styles of solar cookers are very popular: a box-style solar oven and a panel-style cooker. In a solar oven, the pot is insulated by durable oven walls lined with a reflective aluminum interior. Any heat-resistant scrap material, like bricks or fodder, can be used for insulation. By trapping in heat, a solar oven can maintain a uniform temperature and continue cooking for a few hours after sunset. A panel-style cooker, on the other hand, resembles a traditional stove. It only uses a thin plastic bag for insulation, but it has a large reflective surface that can capture plenty of light. Design plans for both styles are available free online. You can either buy one professionally made, or build one from scratch at no cost. Anyone up for a fun weekend project?
One drawback of the solar cooker is that it heats more slowly than a conventional stove. With a solar cooker, meals take longer to cook and require advance preparation. The CooKit model, for example, requires double the heating time and has a maximum temperature of 120°C. This minor nuisance, however, actually provides unintended benefits. A steady, low-heat simplifies cooking since food cannot burn at 120°C. Once set up, cooking a meal requires no extra stirring or monitoring. There’s also less chance to start a fire.
Alas, there is another caveat: a solar cooker will not work in the dark. Extra insulation can help on overcast days, but don’t expect it to work during a blizzard. Because of this limitation, a solar cooker cannot fully substitute for a conventional stove. On sunny days, however, solar cookers are still the most cost-effective, light-impact cooking technology available.
Solar cookers have much to offer to the world’s poor. Solar Cookers International, the non-profit organization behind the CooKit, has distributed over 30,000 solar cookers in Africa. To help Darfuri women, it donated 10,000 CooKits to a refugee camp in Chad. Not only did these cookers help save fuel expenses, they also allowed women to prepare food without the need to venture outside camp, which reduced their risk of assault while attempting to gather firewood.
Solar cookers, however, have been largely ignored in the West. It’s a pity — they are a must-have for the ultralight Greenimalist. They can be built from leftover scrap (cardboard and aluminum) and they use free sunlight as fuel. Panel-style cookers also fold well for easy traveling. What’s more, solar cookers work off-grid, making them useful in campgrounds and homesteads.
One final note: solar cooker operators should wear sunglasses to protect themselves from UV damage. All those concentrating beams aren’t so good for your eyes when you stare at them directly. Then again, wearing a stylish pair of shades might not be such a bad thing, especially if corrugated cardboard and aluminum foil isn’t your idea of green chic.