How Do Solar Cookers Work? Key Uses and Real-World Examples
A solar cooker is a very efficient device. It does not cause air pollution and saves the natural fossil fuel of the earth. This device uses solar energy to cook food. The concept behind this device is that a concave surface reflects and focuses the sun’s heat. The amount of heat is quite large to be able to cook the food. There are three hundred models of solar cookers presently. They range from absolute simple designs to very complicated and advanced technologies. Usually, the largest used solar cookers are simple to build and very cheap. Solar cooking is a solution for people who don’t have access to fuel for cooking. This technology is a boon for them. Moreover, the more we harvest solar energy for cooking, the more clean, fresh, and unpolluted air we breathe. The raw food items are cut into small pieces while cooking. The various uses of the cooker are:
A solar cooker requires a limited quantity of water to cook the food.
The water gets evaporated and then recaptured as freshwater. The solar ultraviolet rays kill the DNA linkages in microorganisms and hence purify the water. Thus water gets distilled.
Iron ore smelting using solar power does not involve the emission of excess carbon dioxide into the atmosphere and hence is a clean process.
We can dehydrate the vegetables and other food items in the solar cooker or oven.
The solar wax melter is a simple solar oven. It has a screen on which we place the raw-wax. It melts slowly and drips into the container below it.
Specially designed solar cookers are used in hospitals and clinics to sterilize their instruments. The doctors prefer using this device as it reduces pollution.
The Three Main Principles of a Solar Cooker
A solar cooker can work only in the daylight. At night it is useless and cannot serve its purpose. There are three main principles based on which the heating takes place in a solar cooker. These are;
The concentration of heat on an object can only occur faster when the sun rays (UV) focus at a particular point. The solar cooker has a reflecting surface made from shiny reflecting material. Metals like chromium, silver, and aluminium constitute these reflecting surfaces.
Black colour absorbs more heat than any colour. Light colours reflect heat. Therefore, most solar cookers are coloured black so that they can absorb more heat to cook well. Also, these cookers are thin so that the heat gets transferred quickly and uniformly to the food.
The solar cooker should be able to trap the heat which it has absorbed. Otherwise, the heat will escape from the food. It will not cook properly. For this reason, the cooker has a lid that tightly covers it.
Solved Examples
1. How to Trap Heat in a Solar Cooker?
The solar cooker uses heat energy from the sun to cook food. The heating of these cookers takes place using simple phenomena called specular reflection. The angle of incidence of the light beam, focussed on the cooker, is equal to the angle of reflection. This phenomenon requires a very smooth surface. No light is scattered away in another direction. This phenomenon used to focus on the maximum heat at a particular point.
2. What are the Advantages of Using a Solar Cooker?
There are various kinds of solar cookers. Using them has several advantages;
Using solar energy for cooking reduces the carbon footprint as no carbon-based fuels or current from the electricity grid is used.
Using less fossil fuel saves the cost spent behind it. It also reduces deforestation and keeps the environment clean.
Cooking can be done at temperatures above 290 degrees celsius with the help of the vacuum tube and parabolic solar cookers.
The conventional solar box cookers can reach up to temperatures of 160 degrees that helps in cooking most food items like bread and vegetables. It also helps in the sterilization of food and instruments.
FAQs on Uses of Solar Cooker: Physics Principles & Applications
1. What is a solar cooker and what is the main principle behind its working?
A solar cooker is a device that uses energy from direct sunlight to heat or cook food. The main principle is to concentrate sunlight onto a receiver or cooking area. It relies on three key scientific concepts:
- Concentration: Reflectors, such as mirrors or polished surfaces, focus sunlight from a wide area onto a small spot where the food is placed.
- Absorption: A black-painted surface inside the cooker absorbs the maximum amount of light and converts it into heat energy.
- Insulation: A transparent glass cover traps the heat (infrared radiation) inside the box, similar to the greenhouse effect, preventing it from escaping and thus raising the internal temperature significantly.
2. What are the common uses of a solar cooker in daily life?
Solar cookers are versatile and primarily used for eco-friendly cooking, especially in regions with ample sunlight. Common uses include:
- Boiling: Preparing items like rice, lentils (dal), pulses, and potatoes.
- Baking: Simple cakes, bread, and muffins can be baked effectively at the moderate temperatures achieved in box-type cookers.
- Roasting: Vegetables and nuts can be slow-roasted.
- Sterilising Water: A crucial application in remote areas to make water safe for drinking.
- Drying Food: Fruits and vegetables can be dehydrated for preservation.
3. How does a box-type solar cooker differ from a parabolic (concentrating-type) solar cooker?
The main difference between a box-type and a parabolic solar cooker lies in their design, efficiency, and the temperature they can achieve.
- Box-Type Cooker: This consists of an insulated box with a glass lid and often a plane mirror reflector. It works on the greenhouse principle to trap heat and typically reaches temperatures of 100°C to 140°C. It is best for slow cooking but cannot be used for frying.
- Parabolic Cooker: This uses a large, curved (parabolic) reflector to focus all incident sunlight onto a single focal point. This design achieves much higher temperatures (often exceeding 200°C), making it suitable for quick cooking, roasting, and even frying. However, it needs to be adjusted frequently to track the sun's position in the sky.
4. Why is the promotion of solar cookers considered important for environmental sustainability?
Promoting solar cookers is vital for environmental sustainability because they use a clean and renewable energy source—sunlight. This reduces dependence on traditional fuels like firewood, coal, kerosene, and LPG. By doing so, solar cookers help combat deforestation, reduce indoor and outdoor air pollution, and decrease the emission of greenhouse gases. This makes them an important tool for mitigating climate change and promoting energy independence, particularly in rural and developing regions.
5. What are the main limitations of using a solar cooker?
Despite their benefits, solar cookers have some significant limitations:
- Weather Dependent: They are only effective on clear, sunny days and cannot be used at night, on cloudy days, or during the rainy season.
- Slower Cooking Time: Cooking generally takes longer compared to conventional stoves.
- Temperature Constraints: Most box-type cookers do not reach temperatures high enough for deep frying or baking certain items like chapatis.
- Attention Required: Parabolic cookers, in particular, require frequent adjustment to keep them aimed at the sun for maximum efficiency.
6. According to the NCERT syllabus, why must the inner box of a solar cooker be painted black?
The inner box and the cooking utensils used in a solar cooker are painted black because black surfaces are excellent absorbers of heat and light radiation. A dark, matte surface absorbs a very high percentage of the incoming solar energy, unlike a lighter or shiny surface which would reflect it. This absorbed energy is converted into heat, which is then trapped inside the cooker, raising the internal temperature to the level required for cooking food.
7. Besides cooking food, what are some innovative applications of the solar thermal principles demonstrated by solar cookers?
The principles of concentrating and trapping solar heat can be applied in various other fields. Some innovative applications include:
- Water Pasteurisation: In community health projects, solar cookers are used to heat water to a temperature that kills harmful microbes, making it safe to drink.
- Wax Melting: Artisans can use them to melt wax for activities like candle making or batik printing on fabrics.
- Medical Sterilisation: High-performance solar concentrators can function as autoclaves in remote clinics without reliable electricity, using the high temperatures to sterilise medical instruments.
