LUANAR : The potential of parabolic solar cookers in climate change mitigation

By | January 29, 2017

LUANAR : The potential of parabolic solar cookers in climate change mitigation

One design of parabolic solar cookers in two sizes

Fuelwood in the form of firewood and charcoal is the dominant source of energy for cooking and heating water in Malawi. Both the rural and urban communities use fuelwood for cooking and for other heating applications.
The dependence on fuelwood is leading into deforestation and the consequences are land degradation and climate change.
Due to increased demand for fuelwood, trees and entire forests are rapidly disappearing and the tress and the forests are losing their capacity to sustain their natural roles in the ecosystem.
Siltation of the rivers and floods are examples of the problem arising from the cutting down of the trees in river catchment areas. Due to disappearing forests, gathering of firewood has now become a major burden to women and girls.
Women and girls are spending a lot of time, travelling long distances as well as exposing themselves to various risks in fetching for firewood. The time that is spent on gathering firewood would have been put into some productive use.
The scarcity of good quality firewood, is forcing some women to resort to using low quality biomass fuels such as maize stalks, maize cobs and tobacco stalks.
The use of low quality biomass fuels is associated with heavy emissions of smoke and therefore exposes households to indoor pollution that is harmful to human health.
A number of solutions have been proposed to deal with the firewood problem. These solutions, which include the use of improved cooking stoves and improved charcoal kilns and the use of alternative fuels (briquettes, gel fuel, ethanol and biogas), have registered limited success.
The solutions that have so far been proposed have overlooked the sun as the major source of inexhaustible energy on this planet. Solar energy is one promising option for cooking in tropical countries such as Malawi because the sun is nearly always overhead throughout the year. The use of solar energy for cooking makes use of solar cookers.
The most powerful type of solar cooker is the parabolic solar cooker. The parabolic solar cooker has a reflective surface that is shaped into a parabola (similar to the inside shape of an open umbrella) in order to focus the sunlight to a single point where the pot is placed. The reflective surface may be made of glass or some other material like Mylar or aluminum foil.
In operation, the parabolic solar cooker collects solar radiation over a large area and concentrates it onto a smaller area where the pot containing the food is located. The temperature of the pot and the food rises, and after some time the food is cooked. The temperature of the cooking pot may range from 150 to 400°C depending upon the intensity of the solar radiation. The temperature is often sufficient for boiling, steaming or baking (100 – 130°C), frying (200 – 250°C) and also roasting or grilling (above 300°C).
Cooking using solar energy has been exploited to a very limited extent in Malawi due to failure to acquire the solar cookers. A number of non-governmental organizations have over the years tried to promote solar cookers but with limited success. These NGOs relied on imported and therefore expensive solar cookers that are difficult to find.
With support from the Shire River Basin Project, the Agricultural Engineering Department at LUANAR embarked on a study whose aim was to demonstrate and facilitate the production and use of low-cost parabolic solar cookers as alternatives to cooking using firewood and charcoal.
The Agricultural Department has developed simple methods for producing parabolic solar cookers using locally available materials to avoid the importation of these solar cookers.
Preliminary results from the study have shown that the locally-produced parabolic solar cooker can be used to cook nearly every food item except nsima. It was possible to cook potatoes, cassava, beans and rice using the solar cooker.
The cooker was also capable of baking cakes and grilling meat. It was observed that nsima required a cooker with a very high power output unlike other foods that can be cooked at low power. As expected, the performance of the solar cooker is affected by meteorological conditions (cloud cover and rainfall). The cooker cannot be used when it is very cloudy or when it is raining because it relies on direct sunlight.
Malawi on average receives about 19 MJ of solar energy per square meter per day. If this solar energy is put into use, each square meter of solar cooker can replace one kilogram of firewood each day, taking 19 MJ as the average heating value of firewood.
The use of the parabolic solar cookers is therefore expected to reduce the dependence on firewood and charcoal and will in turn promote the regeneration of the forests which will in turn serve as carbon sinks. This will in the long run reduce the problem of climate change.
We can safely conclude that if the parabolic solar cooker is produced cheaply and adopted widely by rural and urban households it can make a significant contribution to mitigate the problem of deforestation and climate change. It can also improve the welfare of households by lessening the work that women and girls perform.
Dr Wellam Kamthunzi, Lecturer, Agricultural Engineering Department.

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