Naturally Healthy Earth Friendly Living


"You must be the change you wish to see in the world." - Mahatma Gandhi




By S. Narayanaswamy.

The energy of the sun can be harnessed in a simple way to cook food. There is no need for large complex systems of lenses and mirrors to achieve this task. When sunshine 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 sun for a time the temperature inside exceeds 100 degree C. This is sufficient to cook food. Some more heat input can be achieved by having an exterior reflector. There can be four reflectors also and even reflectors at all the four corners enclosing from all directions. A device based these principles is the solar box cooker. There are several variants of the box cooker – the one made in India resembles a square shaped suitcase with two hinged lids - an inner lid consisting of a glass pane ( to be exact it is a double-glass pane with an air gap for better insulation) and an outer lid holding a single reflector which is simply a glass mirror. There are arms to rest the lids at any desired position. There is a 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 aluminum or fiberglass reinforced plastic (FRP) which is a light and tough material. The solar box cooker weighs about 8-10 kg.

Such box cookers are available in India at a cost of Rs.1500 – Rs.2500 (U.S.$1=Rs.47) depending on the finish.

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 sunshine can be considered good enough to cook. 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 delaying the cooking time somewhat. 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 between 9 am and 12 noon and again between 12 noon and 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" with the solar cooker. The housewife can attend to other chores while the solar is doing its job

A typical loading of the cooker in India is rice with twice the volume in one pot (it can take 200 gms of rice), ‘dal’( lentil) in another pot, cut vegetables ( or whatever) 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 the cooking time. After 2-3 hours when to return you will find all the items cooked. All that remains is for you to take them out and do the "tadka’ or tempering with herbs or spices, on the regular oven, to convert them into complete dishes. You have then made a meal at 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), pasteurize water and even bake bread or cake on a clear day at noon. One can make jams and can fruits. One can use the cooker to get rid of insect infestations from cereals and condiments. One can make sun-dried culinary items in much shorter time in a solar cooker. I have used the cooker even to do repair jobs like restoring soggy biscuits and banana and other chips into oven crisp ones during the rainy season. The solar cooker is a truly versatile device. It is more than a cooker. 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 sunshine 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. You can cook on top of Mt. Everest on a clear day. In fact, the ‘jawans’ – the Indian G.Is.- are using it in Kargil ( the icy heights in Kashmir where they are keeping vigil at the border). It did yeoman service, recently, in earthquake hit Gujarat.

There is no durable cooking device available anywhere in the world which is as cost effective and convenient. Yet solar cooking has not caught on. Why? I suspect it is because most people do not know about it. People might find it strange or odd to cook in the open and may not really know that solar cooking is a feasible proposition. Or they may be thinking it to be a hassle. But the fact is that unless you are introduced to it you will not realize its true and full potential.

It is but true that the solar cooker has certain drawbacks which makes people say it is not an ‘efficient’ energy source. It is slow the cook, it cannot cook on some days when the sunshine is obscured – for that matter even PV devices will not be charged under these conditions. These are not so serious as to label the solar cooker a failed device An effort should be made to convince people that these drawbacks are worth living with. One gets used to it in course of time. Our world is not perfect and we have to make sensible compromises. At any rate those that cannot adjust to it could be left out and those that can should be persisted with. An effort should be made to reach them at the very least. This requires a sustained effort lasting over several years which has been lacking so far. A take it or leave it approach will not do.

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 decentralized cooking instrument imaginable. If you can locate a premises in your home where you can access sunshine you can acquire a solar cooker today and start using it immediately. It makes you energy independent.

Spread over the lifetime of a cooker of, say 15 years, the cost of solar cooking works out to less than 50 paise ( 100 paise make a Rupee) per day as against Rs. 3-5 by any other means. But the cost of solar cooking is loaded upfront. One has to fork out the full life cost of the device in advance. This is a deterrent to investing in a solar cooker and would call for a subsidy element – especially to those below the poverty line – or an installment payment or microcredit system.

It defies logic, but it is true, that solar cookers are not being subsidized by the Indian government (they were till 1994. Some states like Gujarat and Karnataka continued the subsidy after 1994 and perhaps do so even now) but commercial fuels like kerosene and LPG which are imported at great cost and add to the pollution are subsidized. Even other renewable energy systems are subsidized.

There are also cookers called concentrating cookers which are concave mirrors (parabolic in shape) which reflect solar energy to a focal point where a cooking pot can be kept. They are available in several models (Rs. 5000, Rs.55000, Rs.25,00,000 and Rs. 55,00,000!). These can do a faster job of cooking. But they are costlier and inconvenient in many ways – they have to be constantly moved to catch the sun, they cannot cook more than one item at a time, they are large, unwieldy and have to be fixed at a place, they are prone to scratches on the reflecting surface and can be blown away by high winds if not properly secured. For all these reasons they are not as cheap, compact and convenient as the box cooker – at any rate they are not affordable to those that are in need of alternative energy sources. But they are subsidized by the government!

Another type of solar cooker is also now being made in India, the Sunstove – it does not have an outer reflector. It has been popularized in South Africa. The one made in India has a plexiglas window and the reflectors are the shiny sloping sides of the box itself. It has two large sized pots. It is lighter and cheaper – around Rs.1000. It has just commenced production in Kolkata, in an initiative of the Rotary Club. I am sure it has very good prospects.

I have been practicing solar cooking in Trivandrum in India for over 12 years on a sustained basis – an unlikely place for solar cooking because of its higher than average rainfall. I have taken to the solar cooker as one takes to one’s pet dog. I can commend it to everyone with the utmost confidence. If you are not immodest in your demands you will find it hugely satisfying and great fun.

Government of India (GOI) in the ministry of non-conventional energy (MNES) promotes renewable energy (RE) projects . IREDA is their financing agency. But the solar box cooker does not enjoy high priority with GOI. Their sights are set on hi-tech devices – wind energy, photo electricity and so on. In the States in India the ministry operates through the ‘State Nodal Agencies’. They sell RE devices through ‘Aditya Shops’ – ‘Aditya’ is Sun in Indian lore. In theory one can buy a solar cooker at these Aditya Shops. It is doubtful which of them really have solar cookers on the shelf. There are over two dozen manufacturers of solar cookers in India but many are languishing for want of orders. Government, the energy gurus and even the NGOs seem to be distracted by other elitist technologies.

One can see a lot of promotional activity, world over, for photo electricity. So much so that one would be led to think that solar energy cannot be harnessed usefully except in this manner. Photo-electricity is undoubtedly a most elegant technology very suited to bring electricity to people in developing countries living in remote places unconnected to the grid. But to offer it as the cure- all for poverty is a mistake. Governments in developing countries are offering photoelectric devices at subsidized prices without discrimination to one and all. This is a waste of resources. Photo electricity cannot provide the much higher energies required for cooking and other domestic needs. Photo-electricity does not automatically usher in the age of electricity for the poor. It can meet the minimal energy need for lighting. But these PV enthusiasts slur over the much larger energy needs of the poor for cooking.

I have visited numerous web sites on renewable energy, including those on household energy but am sorry to find that very few are seriously talking of solar cooking. There is lot of space devoted to biomass. This is understandable because biomass devices are the existing cooking devices of the poor and it makes sense to set about improving their efficiency. But biomass also depends on firewood which has to be avoided to the extent possible. Biomass systems are messy and not clean. They do not make for energy independence. Solar cooking is really what ought to be promoted seriously. But it requires patient promotional activity which is sadly lacking.

Many individuals and organizations are working in several developing countries promoting cardboard panel cookers such as the ‘Cook It’. They are a good beginning because they are cheap and the people are too poor to afford anything better. But by their very nature they are not durable. I do feel that if solar cooking is to catch on durable solar cookers such as the ones being made in India are required.

I have written a book about renewable energy and the solar cooker. I am a retired officer of the Indian Administrative Service. The title of the book is "Making the Most of Sunshine - A Handbook of Solar Energy for the Common Man". It is published by Vikas Publishing House Pvt.Ltd., New Delhi (E mail: Pages 204. Price: Rs.375 , hard cover. I have also authored a 40 page booklet in Malayalam, the language spoken in Kerala State in India, priced Rs.18, which has been published by the Kerala Literacy Mission.


S. Narayanaswamy
Trivandrum 695 041

(Presently at: 4080, Reedland Circle, San Ramon CA 94583)




Sun Stoves can be found at 88x40rg.gif
Just click on the link, Real Goods-Home and Garden, and search for "Sun Stoves"



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