Energy from the sun

The sun can be described as the earth's powerhouse, solar radiation provides the energy for all the processes that sustain life ~ photosynthesis, the water cycle, plants and even fossil fuels that are nothing more than energy caught in ancient plant matter. The sun's energy can be harnessed through using the sun's heat (solar thermal techniques) or using the sun's light (photovoltaics). The two processes require different technologies and materials. Solar thermal technologies include solar thermal power generation, solar water heating for domestic use and solar cooking. Solar cooking is one of the oldest applications of solar thermal energy.

Solar cooking

Fuel for cooking and baking may be scarce (as for fuel wood) and expensive (as for electricity, gas and paraffin), negatively affecting the family budget and women and children's workloads. Environmental problems such as deforestation, wood fuel scarcity and emission of greenhouse gases caused in part by burning fuels can be traced to the ever-present need for energy for cooking purposes. These are some of the reasons why savings in cooking fuel consumption would be welcome - a challenge for fuel-saving stoves such as solar cookers.

food and bake bread and cakes. No other fuels such as wood, paraffin, or electricity is required, only sunshine! There are four different types of solar cookers, namely solar box cookers or solar ovens, parabolic reflector cookers, indirect solar cookers and heat retention devices. There are probably more than 200 different stove designs in existence but most of them are designed prototypes - there are only a few designs available on a commercial basis. Due to the relative scarcity of solar cookers in the market, low awareness about the products and affordability issues, solar cooking is not yet one of the common solar thermal applications available.

Technology description

The basic types of solar stoves

Box cookers are usually insulated containers with a multiple glass or other transparent material cover. These kinds of cookers depend on the greenhouse effect in which the transparent glazing permits passage of shorter wavelengths solar radiation, but is opaque to most of the longer wavelength radiation. External reflectors such as mirrors may be used to reflect additional solar radiation into the cooking chamber. A double walled insulated box can also serve to hold the heat inside the cooker. Box cookers are easy to move, they don't required tracking to follow the sun, they keep food warm for a long time, are stable and produce no glare. Box cookers are suitable for baking as well as cooking dishes that require a long cooking time.

Concentrator cookers concentrate direct solar radiation, often enhanced by additional reflectors on a cooking pot. The pot is supported in the focus point when the solar radiation is concentrated. They are quite efficient but require the user's attention to keep them aligned with the sun, maintaining good performance. Higher temperatures can be reached than with normal box cookers but baking is limited.

Collector cookers are made up of two parts that often sharing a single casing: a collector for gathering heat and add cooking range for exploiting the heat. Pots and collectors are often separated and a heat transfer medium such as oil or steam is required to convey the heat into the pot. These cookers make use of diffuse and direct solar radiation. They are, however, rather complicated to bold and more expensive than other cookers.

Solar heat retention devices cannot cook food but use residual heat to complete cooking or keep food warm between cooking and eating it. The cooking process is started on any conventional stove or solar cooker and after some cooking time, the pot is removed and placed in a heat retention device. The cooking process is finished without using any more energy. Heat retention devices include hayboxes, hot boxes or hot-bags. The principle is that the pot is placed in an insulated container.Retained-heat cookers consist of boxes or baskets padded with cushions of polystyrene balls, while hot-bags use thing foil paper and insulating padding material in a bag. Using a retained-heat cooker can save between 50% and 75% on fuel use. Heat retention cookers can be used with any type of stove but is especially recommended for use with solar cookers if you want to keep your meal warm for eating in the evening when the sun no longer shines.

How to use a solar cooker

To use a solar cooker, it has to be put in a place that will have sun for 2-3 hours. The food must be put in black pots with tight lids. Using black pots is very important because black will absorb heat while shiny metal will reflect heat and sunlight away from the pot. Pots are either supplied with the solar cookers, or you can use flat-bottomed cast iron pots in box cookers and three-legged potjie pots in the reflector cookers. Alternatively, you can make your own black pots by spary-painting ordinary aluminum pots black. Except for beans or dry grains, which require the normal amount of water, there is no need to add water, especially with vegetables and meat. The cooker must be aimed towards the sun, moving it as required by the type of cooker. Box cookers will only need re-orientation after two hours as the sun moves, while reflector cookers require more frequent tracking. There is no need to stir the food as frequently as usual or to watch the food as it rarely burns or boils over.

A few things to note:

1. Solar cookers require the sun to cook, but a few clouds will not affect them. They can not however cook at night or in skies that are more than half covered with clouds;
2. Any type of food, particularly food that needs a long cooking time (such as beans, samp, rice, meat stews, and porridge) can be cooked in a solar cooker. You can bake bread, cake, scones, and even meringues in a solar cooker, although the box-cookers are more suitable for baking than the reflector cookers;
3. Foods that are not suitable for solar cooking are pasta dishes and deep-fried dishes such as potato chips;
4. Solar cookers will require longer cooking times than with conventional methods. Cooking time depends on the efficiency of your cooker, but generally you can add about an hour to the normal time it takes to cook a specific dish. You will therefore have to plan your cooking and food preparation - don't start half an hour before you want to eat;
5. Longer cooking times are not a problem though, because you can leave the cooker to get on with the business of cooking - you don't need to watch it, stir the pot, or check that the food does not burn. You can do other things instead of cooking as the solar cooker does the work for you;
6. Most people use solar cookers to save fuel and therefore, money. If you use your cooker 2-3 times a week, you can expect to save one third of your cooking energy costs. The more you use your cooker, the more money you will save.

Can solar cooking work for me?

Definitely if you want to broaden your choice of cooking options, if you want to save on your cooking energy expenses, if you are in an area where cooking fuel is hard to obtain and if you want to reduce environmental impacts associated with the use of fossil fuels. It is not suggested that solar cookers should replace all other cooking options, but rather that solar cooking be treated as an add-on service. If you view your solar cooker as an additional cooking device similar to your electric stove, microwave oven, braai fire, paraffin stove or gas cooker, you can fit into your cooking habits to best suit your time and the dishes you want to prepare. Campers and outdoor enthusiasts can use solar cookers to cut down on their wood fuel use and to enjoy a fully cooked meal when they return to their campsite after a day of hiking, fishing or other outdoor activities. Solar cookers can also be used for other tasks, such as sterilizing medical equipment in an emergency, purifying water, drying food such as rusks, preserving food and dying wool and material.

Benefits of solar cooking

1. Saves time which can be spent on other tasks;
2. reduces women's workload by not having to fetch wood or obtain other fuels;
3. Saves money that would otherwise be spent on other fuels;
4. Is healthier as there is no smoke or fumes;
5. Is safe as here is no risk of burns or fire;
6. Ensures healthier food as less water and no oil is needed;
7. Waster can be purified by boiling it in a solar cooker;
8. Once you have paid for your cooker, the energy is provided free from the sun; and
9. It protects the environment