Type I: Dish Solar Cooker
It is a concentrating type parabolic dish solar cooker useful for homes & small establishments. A typical dish solar cooker has an aperture diameter of 1.4 meter and focal length 0.28 meter. The reflecting material used for fabrication of this cooker is anodized aluminum sheet which has a reflectivity of over 80%. The tracking of the cooker is manual and thus has to be adjusted in 15 to 20 minutes during cooking time. It has a delivering power of about 0.6 KW which can boil 2 to 3 liters of water in half an hour. The temperature achieved at the bottom of the vessel could be around 350 to 400o C which is sufficient for roasting, frying and boiling. The cooker having a thermal efficiency of around 50% can meet the needs of around 15 people and can be used from one hour after sunrise to one hour before sunset on clear days. It can be easily dismantled and assembled by anybody and thus may be nicely packed and transported anywhere in the country. The cooker is user friendly as the place of vessel to be kept for cooking is at a level which is convenient for the people to use.
Potential users
The cooker could be useful for individuals in rural as well as urban areas and also for small establishments like dhabas, tea shops, etc. on road sides.
Fuel Savings
The cooker can save up to 10 LPG cylinders/year on full use at small establishments.
Cost
The cost of the cooker may vary from Rs. 3,500 to Rs. 5,000 depending on the type of reflectors used and the salient features provided by the manufacturers. The cookers with imported reflectors having a reflectivity of over 90% will have a higher cost. This should include the cost of accessories like pressure cooker, cap, hand gloves & goggles, cooker manual, packing etc. The transportation cost may, however, be extra which will depend on the distance and the quantity of cookers to being supplied.
Life
Around 20 years for metallic structure. Reflecting sheets may however, have to be replaced once in 5 years due to degradation in reflectivity.
Pay back
1 ½ to 3 years depending on the extent of use & the place of utilization ( for commercial establishments and large families the pay back period is less).
Type II: Scheffler
(Paraboloid Type Community Solar Cooker for Indoor Cooking)
The cooker has been designed by Wolfgong Scheffler, associated with Solar Brucke of Germany and is being promoted by local manufactures & a few NGOs in India for the last few years. The unique feature of this cooker is that it is possible to cook using solar energy within the kitchen itself. The large reflector of minimum 7 sq. m. area standing outside the kitchen reflects the solar rays into the kitchen through an opening in its North wall while a secondary reflector further concentrates the rays on to the bottom of the pot / frying pan painted black. The temperature attained is so high (400 C) that the food could be cooked in a shorter time unlike box solar cooker. It therefore acts like a conventional cooking device with the difference that instead of conventional cooking fuel like gas, electricity or firewood, the food is cooked with the help of solar energy.
Salient Features
Community cooking:
Cooking for about 40 to 50 persons is possible with this cooker. Same is not possible with other types of solar cookers. One dish may take around 1 to 1 1/2 hours depending on the type of dish and solar insolation available. The cooker, however, works nicely in areas where solar insolation is good during most part of the year. It is possible to cook two meals with the cooker in those areas.
Indoor Cooking:
Since the solar rays are directed into the kitchen, it enables cooking indoors. The cook, therefore, does not have to go outside in the sun to load and unload the cooking pots as being done in Box Solar Cooker.
Fast cooking:
Due to high temperature and power at focal point, the cooking rate is significantly higher compared to other solar cookers.
Cooking of traditional food:
Due to high temperature it is possible to cook almost all traditional dishes including making chapattis, purees, dhosa etc. as well as doing `Vaghar'/`Tadka' before adding the vegetables, dal etc. With box-type cookers many of these traditional dishes which requires frying are not possible.
Automatic tracking:
There is a mechanical clockwork arrangement which rotates the outside primary reflector to track the sun automatically. The cook has to set this reflector in focus only once a day in the morning and thereafter for rest of the time the clockwork keeps on rotating the reflector automatically.
Seasonal adjustment:
With shifting of two arms provided in the reflector frame it is possible to change the curvature of the parabolic reflector for seasonal adjustment; thus keeping it fully tracked with the sun during all seasons.
Multiple Use:
During the period when cooker is not in use for cooking, it can be used for hot water production.
Potential users
The cooker could be useful to residential schools, institutional kitchens such as industrial and administrative canteens, religious ashrams, hotels, hospitals, police and armed forces kitchens, etc. One cooker can serve for 40 to 50 people. For larger number of people, more cookers could be installed.
Fuel Saving
Around 35 to 40 LPG cyl./ yr on full use in community kitchens
Cost
Rs. 40,000 to 50,000/- approx. depending on the type of reflectors used & salient features provided by the manufacturers. This excludes the cost of transportation, civil work & pressure cooker (Installation cost is included).
Life
i) Metallic structure : About 20 years. Should be able to withstand high wind speeds.
ii) Reflecting mirrors: Minimum 5 years
O & M expenditure
2 to 3% per annum on an average
Pay back period
4 to 5 years
Ideal kitchen for indoor cooking
• The kitchen wall from where the sun rays will enter should be North facing and should be exposed to open surroundings.
• It should be a single storey building having a slanting roof towards North wall. Otherwise the cooker may have shadow of the kitchen.
• There should not be any other building/structure/trees very near to the kitchen which will cast shadow on the cooker standing in front of the North wall.
• There should be sufficient space in front of the North wall of kitchen to install the solar cooker facing South. 6 to 8 meters distance from the wall should serve the purpose.
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