| Solar Ovens |
| Sunday, 31 August 2008 13:12 |
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The sun’s energy can be harnessed to carry out very practical tasks such as heating water and cooking. One of the easiest ways of transforming the sun’s rays into heat is by using a dark surface, which naturally absorbs the sunshine and becomes hot. A solar oven uses this very same process to work. Solar cooking is the simplest, safest, most convenient way to cook food without consuming fuels or heating up the kitchen. To cook food in a solar oven, you need a reflective surface which focuses the sun’s rays onto a dark surface where the food to be cooked is placed. It might not sound ground-breaking for people living in Malta, but for hundreds of millions of people around the world who cook over fires fuelled by wood or dung, and who walk for miles to collect wood or spend much of their meagre incomes on fuel, solar cooking is more than a choice — it is a blessing. This releases them to participate in more productive activities such as attending school. It also helps to avoid deforestation. For millions of people who lack access to safe drinking water and become sick or die each year from preventable waterborne illnesses, solar water pasteurization is a life-saver. The World Health Organization reports that in 23 countries 10% of deaths are due to just two environmental risk factors: unsafe water, including poor sanitation and hygiene; and indoor air pollution due to solid fuel use for cooking (e.g. wood). The three most common types of solar cookers are heat-trap boxes, curved concentrators (parabolics) and panel cookers. Many variations on these basic types exist. Additionally, several large-scale solar cooking systems have been developed to meet the needs of institutions worldwide. Box cookers cook at moderate to high temperatures and often accommodate multiple pots. Worldwide, they are the most widespread. There are several hundred thousand in India alone. Curved concentrator cookers, or "parabolics," cook fast at high temperatures, but require frequent adjustment and supervision for safe operation. Several hundred thousand exist, mainly in China. They are especially useful for large-scale institutional cooking. Panel cookers incorporate elements of box and curved concentrator cookers. They are simple and relatively inexpensive to buy or produce. Most solar cookers work on basic principles: sunlight is converted to heat energy that is retained for cooking. Sunlight is the "fuel." A solar cooker needs an outdoor spot that is sunny for several hours and protected from strong wind, and where food will be safe. Solar cookers don't work at night or on cloudy days. Dark surfaces get very hot in sunlight, whereas light surfaces don't. Food cooks best in dark, shallow, thin metal pots with dark, tight-fitting lids to hold in heat and moisture. A transparent heat trap around the dark pot lets in sunlight, but keeps in the heat. This is a clear, heat-resistant plastic bag or large inverted glass bowl (in panel cookers) or an insulated box with a glass or plastic window (in box cookers). Curved concentrator cookers typically don't require a heat trap. |
