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20 August 2014
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A bright idea
S Narayanaswamy sheds light on solar cooking
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June 2001: The energy of the sun can be harnessed in a simple way to cook food, without complex lenses and mirrors to accomplish this task. When sunlight falls on a black surface it is absorbed and transformed into heat. Glass has the property of letting in light but not heat. If a shallow glass covered chamber coated black inside and insulated all around is exposed to sunlight the temperature inside exceeds 100 degree Celsius, sufficient to cook food. More heat can be achieved by having an exterior reflector. The solar box cooker incorporates these features.

The author and his wife demonstrate the use of the solar cooker to a Kudumbasree group in Thiruvananthapuram, Kerala. Kudumbasree is a state-funded initiative to combat poverty through programs for women.

The cooker resembles a square suitcase with two hinged lids - an inner lid consisting of a glass pane (typically a double-glass pane enclosing air for better insulation) and an outer lid holding the reflector, which is simply a plane glass mirror. There are arms to rest the lids at any desired position. There is heat resistant rubber beading all round for a good seal at the seating of the inner lid. The lower half of the box is insulated on all four sides and the bottom and has four cooking pots. All the pots are coated black outside with matt finish paint. The cooker has four castor wheels for easy movement. The outer case of the cooker is made of aluminium or fibreglass reinforced plastic (FRP) which is a light and tough material. The cooker weighs about 8 kg.

A Few Manufacturers Of Solar Cooking Devices
  • Fair Fabricators,
    142, Tilak Nagar, Indore 452001.
    Tel: 0731-491488, 421472

  • FRP Point,
    G- 3, Sarojini Nagar, Industrial Area, Lucknow 226008.
    Tel: 0522-437761, 440299

  • Rohitas Industries,
    115/260, Civil Lines, Kanpur 208001.
    Tel: 0512-311223, 314546

  • Geetanjali Solar Eneterprises,
    P-14, Kasba Industrial Estate,
    Phase I, EM Bypass, Kolkata 700078.
    Tel: 033-4420773,2483724

  • Piniball Mfg. Ltd.,
    147, GIDC Makarpura, Vadodara 390 010.
    Tel: 0265-642747, 325469.

Such box cookers are available in India at a cost of Rs.1500 - Rs.2500 depending on the finish. There are two dozen manufacturers in India, mostly in the north - Delhi, Gujarat, Himachal, Madhya Pradesh, Maharashtra, Punjab, Uttar Pradesh and West Bengal.

The solar box cooker takes 2-3 hours to cook food. The cooker has to be moved occasionally, say, at hourly intervals, to face the sun as it moves across the sky. It can cook food only when the sun is shining - not at night, or when it is cloudy or raining. Passing clouds do not matter. If there is a clear shadow behind the cooker the sunlight is sufficient for cooking. It is good practice to wheel out the cooker as soon as the sun is up on the horizon to preheat the cooker. If the sun fails to show up or it is cloudy when the sun is fairly high up in the forenoon it is not a good day for solar cooking. If you have had good sun for an hour at start, even intermittent clouding thereafter will not matter except to delay the cooking time. It is possible that after a cloudy forenoon the haze clears up. If there is prospect of good clear sun for an hour from noon onwards you can still put the cooker to use. On a clear day one can even do two rounds of cooking - say from 9 am to 12 noon and again from 12 noon till 3 pm. The great advantage of solar cooking is its convenience. You do not have to be on your legs in constant attendance. This is because the food never gets overcooked or burnt. You can "load-and-forget" the solar cooker, attending to other chores while it cooks.

A typical loading of the cooker can be rice with twice the volume in one pot (it can take 250 gms of rice), dal in another pot, cut mixed vegetables of two varieties in the two other pots. Instead of moving the cooker once in an hour you can even keep the cooker fixed in the 'average' position - both in relation to the east-west plane and in relation to the azimuth - of the sun during that interval. In 2-3 hours you will find each of the items cooked. All that remains is for you to take them out and do the "tadka' or temperng with spices, on the regular oven, to make them into complete dishes. You have made a meal at near-zero cost in terms of fuel and in terms of the environment.

One can cook not only food, but also roast nuts, dry vegetables and fruits (taking care to keep the glass lid slightly open to control the heat input), pasteurise water and even bake bread on a clear day at noon. The solar cooker is very versatile machine. A solar cooker kept out in the sun is like an oven kept switched on in the 'on' position. You can place anything in it anytime and take it out when done. What is important for solar cooking is not how hot the sun is but how clear the sunlit sky is. In most places in India one can cook for 70-80% of the days in a year. One can thus solar-cook in all seasons, with unmatched cost-efficiency. Yet solar cooking has not caught on. Why? I suspect it is because most people do not know about it. Also, potential users might find it strange [or a hassle] to cook in the open, and may not really be convinced that solar cooking is a viable proposition.

The solar cooker is a lifetime asset. Handled with care it can last 15 years or more. There is no moving part in it to go wrong. The only maintenance required is an occasional coat of black paint on the inside of the cooker and on the outer surfaces of the cooking pots. The solar cooker can be used both in the rural and urban sector. In the rural sector it saves village woman from having to trudge for miles in search of scraps of firewood and spending her lifetime in smoke-filled kitchens. In the urban sector it saves energy on kerosene and LPG and makes cooking easy.

The solar cooker is the most self sufficient and decentralised cooking instrument imaginable. You can cook on top of Mt.Everest on a clear day. In fact our jawans are using it in Kargil. It did yoeman service in earthquake hit Gujarat. Spread over the lifetime of a cooker of, say 15 years, the cost of solar cooking works out to leass than 40 paise per day as against Rs. 3-5 by any other means. But the cost of solar cooking is loaded upfront. The ordinary buyer is hit by the immediate cost. This is a deterrent to investing in a solar cooker. This would call for a subsidy - especially to those below the poverty line - or a deferred payment system.

The government, however, is strangely indifferent to its potential. Bulky, concentrating solar cookers - with concave parabolic mirrors - which cost between Rs.5,000 and Rs.5,500,000 attracto government subsidies, but far more effective and inexpensive solar box cooker does not! Subsidies on the box cooker were withdrawn in 1994, and only a few states like Gujarat and Karnatka continued the subsidy after 1994. Commercial fuels like kerosene and LPG which are imported at great cost and add to the pollution are subsidised by the central government. Even other renewable energy systems are subsidised.

Another type of solar cooker is also now being manufactured in India, the Sunstove - it does not have an outer reflector. It is light-weight. Instead of glass pane it has a plexiglas window. It is also cheaper, I have tried it out and it is effective. It has just commenced production in Kolkota. I am trying to impress on GoI the need to develop this and other low cost models. I have been practising solar cooking in Trivandrum in India for over 12 years on a sustained basis, and recommend it to everyone with the utmost confidence. Despite the downside of being slow and unworkable in certain weather conditions, you will find it hugely satisfying and great fun.

The government of India, in the ministry of non-conventional energy (MNES), promotes renewable energy (RE) projects. IREDA is their financing agency. Disappointingly, the solar box cooker does not enjoy high priority with GOI. Their sights are set on hi-tech devices - wind energy, photoelectricity and so on. In the states the ministry operates through the 'State Nodal Agencies', which sell RE devices through 'Aditya Shops'. In theory one can buy a solar cooker at these Aditya Shops, although it is doubtful how readily that theory applies to the solar cooker! If you draw a blank with them you can go directly to the manufacturers. [a brief list is included on this page]. Feel free to write me with your questions, additionally.

Visit http://mnes.nic.in/frame.htm?majorprog.htm to know about the solar cooker programme in India, and a full list of manufacturers. In addition there are unregistered units also making solar box cookers in Bihar and Tamil Nadu.

S Narayanaswamy
June 2001

S.Narayanaswamy, 68, is a retired officer of the Indian Administrative Service, and the author of Making the Most of Sunshine - A Handbook of Solar Energy for the Common Man, published by Vikas Publishing House Pvt.Ltd., New Delhi and available for Rs.375. (E mail the Publisher: orders@vikas.gobookshopping.com.

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