The solar bowl
The Cuisine Solaire Pour Tous, or Solar Kitchen, the collective kitchen of Auroville, takes its name from the huge solar bowl that is incorporated to harness solar energy for cooking. The ferrocement base of this stationary bowl is already built and faces south. It is 15 meters in diameter and 7 meters above ground level. The sun's rays, trapped by a huge hemispherical mirror, focus on a cylindrical boiler which follows the sun's position by means of a computerised tracking device. On a clear day, sufficient steam at a temperature of 150°C can be generated in this boiler to cook two meals a day for 1,000 people.
John Harper, who is part of the team who built the bowl, has been interested in the use of solar energy for many years. During the mid-seventies he spent two years working with Dr. Chamanlal Gupta in the solar energy department at the Sri Aurobindo Ashram, Pondicherry. In the early eighties, John built a prototype solar concentrator of 3.5 diameter at the Centre Guest House that was functional for about two years before it fell into disuse.
"In those days," says John, "prototype solar concentrators of 10m diameter and 20m diameter were being developed at Marseilles (France) and at the University of Texas in the States to prove the concept of using a 'bowl' as a concentrator to tap solar energy. I guess, because of the oil embargo in the '70s, there was an interest in developing other forms of energy. But unfortunately, after the supply of oil was guaranteed again, interest and subsequent research into solar bowls died down in the West.
"The only other large solar cooker in use in India is located at Mt. Abu in Rajasthan. This cooker has a capacity of cooking for 1,200 people and consists of 24 separate parabolic reflectors, each with a reflective area of 7.5 m. We decided upon a solar bowl with a single concave mirror rather than separate parabolic reflectors, because stability of the whole system is an essential factor for us given the strong winds that prevail during the monsoon. Though our design differs from theirs, we have had a fruitful exchange of ideas and information with the team at Mt. Abu. Incidentally, our main solar scientists, the late Sylvie Rousseau, had a close contact with Bernard Authier who developed the bowl in France, and the design of our boiler and concentrator are based on the French model.
"One of the problems I had when I built my first model at the Centre Guest House was devising a system to track the sun. Now, because of our experience in putting together the Matrimandir heliostat to supply a steady beam of light into the Chamber, we have the knowledge to handle this technical aspect.
"To me, building this bowl has been one step towards the future. With this bowl we will be producing steam for cooking, but eventually the heat that you trap could be used for a variety of purposes such as pumping water, producing mechanical power, industrial process heating, etc. One can envision the whole of our Industrial Zone running on solar energy..
"It is a question of orientation. Walk across an open field on a bright sunny day - you can feel yourself being roasted and scorched by the burning sun, or you can feel a great joy in the perception that you are being bathed in a powerful flood of rich golden energy!"
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