Cooking under the sun
Solar cookers work by harnessing the energy from the sun in the form of light, diverting it to a targeted spot and trapping it to heat the food. There are many benefits of solar cooking: low upfront investment; no running cost; little maintenance; and best of all, environmentally friendly. In developed countries, they are used mainly due to environmental consciousness, while in under developed and developing countries they are used because of the acute scarcity of cooking fuel. In interior Sarawak, where the transportation cost of fuel is high, solar cooking can be a very beneficial alternative.
Solar cooker versus solar electricity
Solar cooking is a technology for cooking using the native form of energy from the sun. That way, there are little conversion losses and solar cooking can be very efficient. Energy from the sun is used as a primary form of energy to heat the cooker and cook the food. Whereas in solar electricity, there are photovoltaic (PV) processed to produce electricity and there is need for the storage of electrical energy.
Solar cooker in Sarawak
Through sheer enthusiasm and interest in these technologies, Ir. Allen Liew, an electrical and telecommunication engineer and his group of friends started to work on solar cooker in 2007. Their experiments proved that solar cooking is both possible and practicable in Sarawak.
Cooking time using solar cookers varies depending on weather conditions. On sunny days, solar cookers can cook food almost or just as fast as conventional gas or electrical stoves. Furthermore, due to the nature of the radiated heat in a solar cooker, food tastes better and more nutrients can be retained. In addition, food cooked in a solar cooker can be left unattended as it will not burn.
Solar cooker and RES in Sarawak
Rural Electrification Scheme (RES) that connects grid electrical power to the rural settlements in Sarawak managed to address the needs for lighting. However, the group observed that rural forks do not cook using electricity for two reasons. First, the electrical capacity allocated to them is not sufficient for them to use electric oven or cookers.
Electrical cookers or oven normally consume a big amount of electrical power and therefore not viable for users under the RES. Secondly, because of their high power consumption, electric cookers are relatively expensive to use. The high electricity bill could be a financial burden to the rural fork.
Solar cookers could be an answer to the high transportation charges of fuel in interior Sarawak.
There are obvious benefits in using solar for cooking. Due to environmental, economic, and health reasons, reducing dependence on firewood and conventional fuels, and increasing the use of free and renewable solar energy are important global goal, and should also be our goal. Solar cookers can be significant labour-saving devices since there is no need to gather firewood and so on.
It was reported that more than 35 million m3 of firewood is burned in the savannah region alone each year and it is estimated that Nigeria will be completely barren in year 2020 judging from the current depletion rate. Whereas the United Nations Development Programme (UNDP) predicted that 70% of fuel wood consumption can be replaced by renewable energies like the sun.
How solar cookers work
Solar cookers apply solar thermal principles, where solar energy is used to heat cooking utensils such as a pot, which heat the food inside. It is estimated that the sun's radiation reaching the earth surface is about 1KW/M². That explains why a laboratory magnifying glass is able to focus enough energy from the sun to start fire on a piece of paper!
Solar rays may be collected by means of a funnel, parabolic or even a sheet of slander plate collectors. The collector may be made of cardboard, plywood, with tinted reflective sheet such as kitchen aluminum foil. It may also be made from a polished metal sheets or mirror.
Solar energy is directed to the target by the adjustment of the angle of the reflectors. Since Sarawak is sitting almost (4 deg south) right on equator, the reflectors may be omitted, though they are added advantages.
Solar heat must be trapped. This is most effectively done by using a black object or a blackened surface. Pots or other cooking utensils may be turned into an effective heat trap by painting them black. Also, it is also equally important to provide an air insulator outside of the pot to prevent the loss of heat. This may be achieved by insulating the cooker by means of a clear glass enclosure or a simple plastic bag.
Usage of solar cookers
Solar cookers are used widely in many countries across the globe. Americans are the active promoters of solar cookers, while the North Africans are the major users and benefit most from this technology. Solar cookers are also widely used in the Middle East as well as the Indian subcontinents. Our neighbouring countries, Vietnam and Indonesia are users of solar cookers. In Vietnam, through the work of Solarserver organisation, a factory is currently being built to manufacture solar cookers, which would then be distributed to the rural poor.
Types of solar cookers
Solar cookers may be classified into three categories: box cooker, panel cooker and parabolic cooker. Each type of cooker has its strengths and weaknesses. Box cookers are simplest to construct and can be built using two cardboard boxes of different sizes. The smaller box is inserted into the bigger one to form a double insulated chamber. The inside of the cooker is lined with a reflective sheet, such as aluminium foil, that acts as a reflector. A piece of glass, which may be double- glazed, is used for the top part to allow the diffusion of sunlight, but prevents heat from escaping. This variation is the most used model in the USA. However in his experiment, Allen Liew found that the solar box cooker did not produce promising results. It did not generate enough heat to allow food to cook properly.
Panel cookers or funnel cookers are bigger than solar box cookers and more difficult to construct. However, after the initial algebraic calculation, a solar panel can be reproduced easily by using templates. This variation consists of a cooker chamber, which may be constructed using plywood or cardboards. The inner wall of the cooking chamber is lined with reflective sheet, such as aluminium foil. A panel or funnel cooker can have one or more pieces of reflector.
Parabolic cookers are more difficult to construct manually. This variation works by converging solar energy into a particular focal area i.e. the cooker's surface. Parabolic cookers can produce intense heat on the cooking surface, which makes it possible to fry food and bake cakes.
However, the reflector in this cooker can be glaring and one must wear an effective protection for the eyes when cooking using this device. Parabolic cooker is difficult to construct with precision manually. This is because of the difficulties in achieving the required precision in the construction of the parabola.
The team constructed several units of the different types of solar cookers to verify their suitability for use in Sarawak. For ease of identification and addressing, the solar cookers built by Allen are called SIAP, which stands for "Solar In Actions Panel". These solar cookers can reach around 120c in a clear sunny day.
The solar cookers were used to cook various types of food including sausages, eggs and cake. Eggs can be "boiled" in a solar cooker with the shell intact. It will take about an hour to boil four chicken eggs on a sunny day.
Eggs can also be steamed using a solar cooker. In this case, the eggs are broken and spread on a plate and placed inside the cooker. It will take around 40 minutes to stream two chicken eggs.
It can also be used to bake cakes. In the experiment, an 8" cake with about 2" of thickness took about an hour to cook.
The team has so far constructed and tested about five different models of solar cookers in Kuching. The results of their experiments prove that solar cooking is a possible and viable alternative to conventional cooking here.
The solar funnel cooker appears to be the best amongst all the models. Here, solar cookers shall be over designed so that they can heat promptly when the sky is clear.
The solar funnel cooker that the team constructed and tested worked well as a heating chamber and could produce results similar to the steaming and boiling methods using conventional stoves. In their experiments, the team was able to cook rice, boil eggs, steam cakes and bake sausages. The team is certain that this method can be used to cook various types of Asian dishes just as effectively as using gas, electric cookers or firewood.
Uses of solar cookers
Based on estimates, a solar cooker should cost around RM300. This price is expected to come down when they are produced in reasonable quantity. The solar cookers do not incur any running cost and there are no consumable parts. Solar cookers also require low maintenance and replacement parts for these devices are available locally.
Potential use of solar cookers include general heating, boiling, steaming, frying, baking and etc.
They may also be used on the farm where farmers can cook their meals. Also food cooked using solar cookers won't burn.
As a pasteuriser, solar cookers can turn fresh water into safe drinking water. For instance, jars of fresh water can be placed inside a solar cooker together with a pasteurisation temperature indicator in the morning. The indicators will tell at the end of the operation whether the pasteurisation process is successful or not. If the operation is successful, the water can be store and consumed.
Alternatively, solar cookers may be used for disaster relief operations. Sould basic amenities be cut off in disaster scenes, resources and cooking fuel can be scarce. Solar cookers may come in handy.
Solar cookers can also be a useful tool in institutions of learning. They can be used to educate the young on the wonders of the universe and the importance of the conservasion of earth and its resources.
Further works should be carried out in the research and promotion of solar cookers in the State, and it is Allen's hope that the people's representatives, ministers and relevant departments as well as organisations can assist in the funding and promoting of cooking with solar energy in Sarawak.