Solar Cooker is an answer to a housewife’s problem of saving fuel and time, providing nutrition food and eliminating smoke from burning of wood etc. is today’s new device known as the Solar Cooker. In our country where we have sunshine for at least 300 out of a total of 365 days, this device can be of great utility. Not only can the day’s cooking be done but this device can also be used as a hot case because it retains heat for four to five hours after the cooking is over.
Types of Solar Cooker
The available designs of solar ovens fall into three main categories: the box, parabolic, and panel designs. The feature common to each oven design is the shiny reflective surface that directs the sun’s rays onto a dark cooking vessel. Each category has advantages when compared on their heating ability, ease of construction, ease and safety of use.
1. Box Cooker Solar Ovens
2. Reflective Panel Solar Cookers
3. Parabolic Solar Cookers
4. Solar portable oven
Box Solar Cooker
Box cookers are the most common type made for personal use. There are over several hundred thousand in India alone. Despite the name “box” cooker, they are made in both circular and rectangular shapes. They consist of an enclosed inner box covered with clear glass or plastic, a reflector, and insulation. There is a wide variety of patterns and plans for the box cooker. While they do not heat quickly, they do provide slow, even cooking and are extremely cheap to make. Box cookers are very easy and safe to use, and fairly easy to construct.
Parabolic Solar Cooker
Reflective materials are used to concentrate light and heat from the sun into a small cooking area, making the Sun’s energy more concentrated and therefore more powerful, resulting in the fastest cooking times of all Cooker designs.
Parabolic cookers require more precision to focus the sunlight on the cooking vessel and are therefore the most complex design to build. If the sunlight is not focused exactly on the cooking vessel, the food will not cook efficiently.
Panel Solar Cooker
Panel cookers are flat reflective panels which focus the sunlight onto a cooking vessel without the inner box common in box cookers. Panel cookers are the easiest and least costly to make, requiring just four reflective panels and a cooking vessel, but they are unstable in high winds and do not retain as much heat when the sun is hidden behind clouds. The diagram shows a panel cooker with a dark cooking vessel and thermometer all wrapped in a plastic oven bag.
Advantages Of A Solar Cooker
1. As solar cooker does not consume any conventional fuel or electrical Energy, it saves fossil fuels, wood, electricity etc. which are otherwise required to cook the food.
2. It does not emit any smoke or smell and hence does not pollute the Environment. There is thus no chance of causing cancer and affecting Eyesight or lungs.
3. It does not require constant attention while cooking and hence saves Time which can be utilized for some other productive work.
4. As it is a slow cooking device, it preserves the nutritional value of the Food.
5. It can be used for cooking three to four items at a time.
6. There is no possibility of causing accidents like catching of fire, Bursting of gas cylinders, electrical shocks etc. and hence is safe To handle.
7. It does not have sophisticated components and hence is easy to Operate.
8. It can be used for cooking both the meals.
9. It keeps cooked food hot for four to five hours.
It saves money.
Limitation Of A Solar Cooker
1. It does not work at night.
2. It does not work as well on a cloudy day.
3. In the early morning, late afternoon or even partly cloudy days, its performance is not so good. However the inside of a solar cooker even in such cases, may be sufficiently hot to be used as hot box.
4. It cannot be used for preparing chapattis.
5. It cannot be used for trying purposes.
However, in spite of all these limitations, if a solar cooker is used throughout the year, it does result in the saving of a substantial amount of cooking fuel and contributes towards the economy of a family.
How Does A Solar Cooker Cook
In normal cooking heat from the open fire is transferred to the cooking vessel. In this process, a large amount of heat is wasted from the fire to the environment, Heat is also lost in the form of steam which comes out from the cooking medium carrying 540 calories of heat (which is the latent heat of vaporization)per gram of water. Though these facts are well known, it is surprising that we still allow a large amount of heat loss in cooking with our electric heaters or wood/gas stoves.
In rural areas, wood stoves or open challahs are quite common. The efficiency of these stoves or challahs is extremely low. As a result a large amount of fuel is wasted during cooking. The use of solar cooker can help in cutting down the use of fuel wood which is playing havoc with forests. During non-sunny periods, the use of new improved challahs can further help in saving the fuel wood.
The solar cooker commonly known as Hot Box consist of a well-insulated box or tray , the top of the box and the inner surface of the tray which is exposed to the sun is painted dull black and is covered by one or more transparent covers. The purpose of these transparent covers is to trap heat inside the solar cooker. These covers allow the radiation from the sun to enter inside and get absorbed by the blackened surface and also reduce the heat loss from the hot black absorber.
Because of this, the temperature of the blackened absorber increases and heat up the space inside to temperature up to 150C ON A CLEAR SUNNY DAY. The temperature with cooking pots inside remains about 110C which is adequate for slow cooking of many items.
How To Cook In Solar Cooker
- Carry out the preliminary planning for the recipe in advance. In case of cereals etc. soak them in water overnight before cooking. Similarly for baking bread and cakes etc., soften the ingredients in advance.
- Keep the Solar cooker in the sun in open space free from any shadow. Adjust the cooker in such a manner that the reflecting mirror faces the sun and adjust the angle of the mirror so as to let the reflected rays fall on the transparent glass lid. Tighten the position fixing hinges of the mirror in this position.
- Put the intergrading’s as indicated in the list of recipes in the cooking pots. Open the glass lid of the cooker, place the cooking pots inside the cooker and close the lid properly. It is advantageous to adjust the direction of the cooker after every 25-30 minutes such that the mirror always faces the sun.
- The performance of cooker and hence the cooking time in a solar cooker will depend upon intensity of solar radiation and ambient temperature. During winter season radiation and ambient temperature. During winter season and also during slightly cloudy days, the cooking time may be much more than that indicated in this booklet. During thickly cloudy days, the cooker may not work at all. The time of cooking for various recipes indicated in this booklet is for about 800 Watts/m2 of solar isolation when ambient temperature is 20-25C.
- During cooking the temperature inside the cooker should not fall below 100C. The cooking can be done between 10 A.M. and 3 P.M. during winter months and 9A.M. and 4P.M. during summer months. The time taken to cook four dishes at a time will depend upon the type of food to be cooked and season of the year and will vary between 1 hour to over 2. it is to be remembered that solar cooker cooks food only during sunny days and hence can not replace other cooking devices/methods fully. It can only supplement the use of fossil fuels ,wood, electricity etc. and therefore can result in saving commercial fuels and wood. In addition, it also helps in reducing pollution and harmful effects of burning fossil fuels, wood and cow dung etc.
What Can You Cook In Solar Cooker
You can cook a large number of items, which are needed for our daily meals, in a solar cooker. Some of the common items which could be cooked in a solar cooker are listed below:-
1. Rice, khichri, pulao, biryani, kheer etc.
2. Pulses – gram, mung, urad etc.
3. Cereals – grams etc.
4. Vegetables –cabbage, cauliflower, potatoes, carrot, peas, beans etc.
5. Bread, biscuits, cake, nankhatai etc.
6. Fish, chicken,meat,curry,shami,kababs etc
Some instructions For Cooking In Solar Cooker
- During cooking use only as much water as required.
- Vegetables ,should be cleaned and cut into small pieces.
- Keep the containers covered while cooking. In case of baking bread and cakes etc., it is not necessary to cover the container.
- The cereals should be softened in water before cooking.
- The level of water along with ingredients should not rise beyond the half-way level in the cooking pots.
- Once the cooking pots are placed inside the cooker, the lid should not be opened.
- When the food is ready, the lid should be opened fully. The moment the lid is opened, steam will escape. It will be very hot inside. Be careful otherwise there is a danger of getting steam burns.
- Once the cooking is over, clean the cooker with a dry piece of cloth and then close it. Next day when you reuse it, clean the cooker before using.
- Keep the cooking tray and outer surface of cooking pots always painted black.
- Keep the cooker in the sun for at least 45 minutes before loading it with the cooking pots. This will keep the cooker ready for cooking and cooking time will also be reduced.
- Solar cooker should be handled carefully as it has some glass components.
- While moving the cooker from inside the house to open sun or vice versa cooking pots should be taken out.
- While removing the cooking pots after the food has been cooked, gloves or cloth napkins should be used. The face and body should be kept as far away as possible to avoid getting steam burns.
- The double glass lid should be held carefully while removing the pots.
- The food items like root vegetables, kheer and other milk preparations etc. which require low and gradual rise in temperature are cooked very well in solar cooker. These items should always be placed in covered cooking pots.
- The food items which require roasting are also cooked well. These , however, should never be covered. Further-more, the cooking pots should be greased at the bottom and the food to be cooked should be smeared with oil.
- The egg can be boiled in water or baked without water. For frying, the containers should be greased and raw eggs broken on it.
- For cooking in solar cooker, spices according to taste should be added before or after cooking but not during the cooking.
- The pickles which are prepared by keeping in the sun, can be prepared in a shorter time in solar cooker. At the same time, they are protected from dust, dirt and insects.
- When the cooker is not in use, it should be closed and kept in a sheltered place.
- If the black coating on the cooking tray and food containers has worn out, a dull black paint should be applied to them.
- Both sides of the glass lid and reflecting surface or mirror should be wiped and cleaned with a soft clean duster before and after use.
- Before keeping the solar cooker inside after cooking, the lid should be left open for 10-15 minutes to allow it to cool down.