a) Passive solar energy
- As you know some of the earliest uses of solar energy were passive in nature such as to evaporate sea water for producing salt and to dry food and clothes. In fact solar energy is still being used for these purposes. The more recent passive uses of solar energy is for cooking, heating, cooling and for the daylighting of homes and buildings. The effectiveness of passive solar energy depends on good building design; no mechanical means are employed in passive use of solar energy.
Passive use of solar energy for cooking
- The energy from the sun can be harnessed, to cook food without any large, complex systems of lenses or mirrors. We all know that when sunshine falls on a dark surface, it is absorbed and transformed into heat energy. Glass is bad conductor of heat but if a shallow glass covered chamber painted black inside and insulated all around is exposed to sun for some time the inside temperature would soon exceeds upto 100oC which is sufficient to cook food. On a hot summer day the temperature inside the solar box cooker will easily becomes140o C. Solar cooker takes 5-6 hours to cook food. The solar box cooker is the poor man’s device for direct use of renewable source of energy. In Indian conditions with plentiful sunshine, we can use a solar box cooker for cooking of food. The great advantage of solar cooking is its convenience because the food will never get overcooked or burnt. Apart from its “load-and-forget” quality, the food cooked in the solar cooker is also more tender and retains most of the nutritive values. But this comes at a cost is a slow process and take longer time i.e. solar cooking.
Definition of pollution and pollutants
Brahmakumaris’Ashram at Mount Abu (Rajasthan, India) – World’s largest solar steam cooking system
India may be justifiably proud that the world’s largest solar steam cooking system is operating in the Brahmakumaris’Ashram at Mount Abu in India. Here the solar energy is concentrated by a battery of concentrators /mirrors to convert water into superheated steam. The system can cook for 10,000 people. It was constructed at a costs one crore of rupees excluding the labour of the ashram inmates.
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Passive use of solar energy for daylighting
- Daylighting is using natural sunlight to light building interiors. Day lighting technologies are designed to maximize natural light for illuminating the interior of buildings. These may be in the form of core lighting when the building may have a central atrium to allow entry of maximum sunlight.
- The most recent technology is hybrid solar lighting which collects sunlight and send it though optical fibres into buildings where it is combined with electric light in “hybrid” light fixtures. There are sensors in the room which keep a steady lighting level by adjusting the electric lights based on the sunlight available. This new generation of color lighting combines both electric and solar power.
- Passive solar systems are maintenance free. There are no moving parts and so no energy is expended for heating or cooling a building and hence, there are no operating costs. The only major problem is that passive solar heating, cooling and lighting system can be used only in specially designed buildings. Daylighting of business and commercial buildings provides a higher quality of light and improves productivity and health and at the same time results in substantial saving on electric bills.