1. SOLAR COOKING TECHNOLOGY

2. Why Solar Cookers are needed
High cost or Unavailability of commercial fuels – Kerosene, Coal, Gas, Electricity
Deforestation caused by Increasing Firewood Consumption
Use of Dung and Agricultural Waste as Fuels Instead of for Soil Enrichment
Diversion of Human Resources for Fuel Gathering

3. Heat losses during cooking
The principle ways of cooking food are Boiling, Frying, Roasting, and Baking
Heat losses during cooking
Vaporization of water : 35 per cent
Heating food to boiling : 20 per cent
temperature
Convection losses from vessel : 45 per cent
Solar cooker should be designed to provide about 1.0 kW of energy which can be obtained with 2.0 sqm of collector area with 50 per cent efficiency.

4. Principle of Cooking
The quantity of heat required for physical and chemical changes involved in cooking are small compared to the sensible heat of increasing food temperature and energy required for meeting heat losses that normally occur in cooking.
Once the contents of the vessel have been sensibly heated up to the cooking temperature (100C), the speed of cooking is practically independent of heat rate as long as thermal losses are supplied.
Differences in the time required to cook equal quantities of food in cookers of various heat supply capabilities are due mainly to different sensible heating up periods.

5. Reasons for the non-acceptance of the solar cookers
Too expensive for individual family ownership
Incompatible with traditional cooking practices
too complicated to handle
cooking can be done only in the direct sun
can not cook at night
can not cook in cloudy weather
can not cook indoors
danger of getting burned or eye damage
are not locally available
less durable; needs repair or replacement of parts which are not easily available
The cooker needs frequent adjustment towards the sun and exposure of the cooking pot to the blowing dust and sand effected the food taste
Easy availability of alternative cooking fuels like wood and fuel wood
There is no provision of storing the heat therefore cooking of food was not possible where there are clouds or sun is not strong
No proper education, training and involvement of women folk

6. Direct or focusing type solar cooker
Types of Solar Cookers
Direct or focusing type solar cooker
In these cookers some kind of single or multifacet solar energy concentrator (parabolic, spherical, cylindrical, fresnel) is used which when directed towards the sun focus the solar radiation on a focal point or area where a cooking pot or frying pan is placed. In these cookers the convection heat loss from cooking vessel is large and the cooker utilizes only the direct solar radiation.

7. Direct or focusing type solar cooker
Design variations
Parabolic / spherical / cylindrical reflector
Single mirror or mosaic type
Diameter : 0.5 m – 8.0 m
Focal length: 0.3 m – 5 m
Manual / automatic tracking
Temperature achieved: 150C - 450C
User – single family / community

8. Direct (focusing) type solar cookers

9. Indirect or Box type Solar Cooker
In these cookers an insulated hot box (square, rectangular, cylindrical) painted black from inside and insulated from all sides except window side which is double glazed is used. Single plane or multiple plane reflectors are used. Some times these are also known as oven type solar cookers. These can be electrical cum solar cookers and some cookers utilize a kind of latent heat storage material.

10. Indirect or Box type Solar Cooker
Design variations
Square / rectangular / oven
Single, double or multiple plane reflectors
Frequent tracking not required
Temperature achieved : 100C - 250C
User single family / community
Electrical back up
Latent heat storage material

11. Box type Solar Cookers

12. Advanced type Solar Cooker
In these cookers, the problem of cooking outdoors is avoided to some extent. The cookers use either a flat plate collector, cylindrical (PTC) concentrator, or a multifacet or large parabolic (mosaic type) concentrator which collect or focuses the solar heat and transfers or reflect from a secondary reflector to the cooking vessel. The cooking in some cases can either be done with stored heat or the solar heat is directly transferred to the cooking vessel in the kitchen.

13. Advanced type Solar Cooker
Design variations
Cooking can be done indoors also
Storage of heat is possible
Frequent tracking required / not required
Temperature achieved upto 350C
User – single family / community
Flat plate, cylindrical or large mosaic parabolic reflector

14. A Few Advanced Type Solar Cookers

15. Feasible Applications of Solar Box Cooker
Solar Box Cookers have been found to be technically feasible for various applications of cooking such as rice, khichadi, pulao, basundi, biryani, kheer, dal, bread, biscuits, cakes, nankhatai, dhokla, fish, chicken, meat, egg etc.

16. Box type Solar Cooker

17. BOX SOLAR COOKER

18. Solar Box – type Cooker : Design Details
Component
Material
Thickness / size
Requirements / Remarks
Outer Box
Galvanished iron
Aluminium
FRP
0.48 mm thick
(60 x 60 x 17 cm)
0.56 mm thick
2 mm thick
Resistant to ultraviolet radiation and atmospheric variations
Inner Cooking Box
(50 x 50 x 10 cm)
Painted dull black
Should not touch outer body
Insulation (Back and side)
Glass fibres in the form of pads
5 cm or more thick
k = W/m K
Free from resin binders Stable upto 250C
Glazing (Double glass lid)
Water white glass (Temperated / toughned)
3-4 mm thick
50 x 50 cm size
spacing between sheets
1 cm
Double glass system must be air tight
Transmittance > 85%
Reflectors
(Mirrors)
Silvered or
Glass aluminized
4 mm thick
54 x 54 cm
Reflectivity > 85%
Scratch resistant
Resistant to solar radiation and atmospheric variation
Cooking Containers
Aluminium alloy sheet
Stainless Steel sheet
1.2 mm thick
Two pots – dia 200 m
Two pots – dia 150 mm
Depth of pots – 67 mm
Dull black painted stable upto 250C
Very good adhesive characteristics

19. Solar Box-type Cooker : Cooking Time for Recipes
It takes about 2 – 2.25 hours for cooking depending upon the kind of food and season. Different items like dal, rice, vegetables etc. are normally cooked simultaneously in separate containers. The time taken for cooking is less in summer than in winter. Based upon experience following are the results for cooking time for various recipes:

20. SK - Type Solar Cookers (SK-10, SK-12, SK-14, SK-98)
SK – Solar Cooker uses parabolic reflector made of thin, hard aluminium sheets with protected, high reflecting surface mounted at a rigid basket structure.
Reflector with short focal distance for safety reasons, long tracking intervals and high efficiency.
Cooking pot in a standard 12 – litres pot of black enamelled steel with a diameter of 28 cm.
Tracking is done by moving the whole cooker (azimuth) and by turning the reflector around the horizontal axis (elevation), adjustment of the reflector to the sun by use of a shadow indicator.

21. Technical Data (SK Type Solar Cooker)
Reflector diameter : 140 cm
Nominal effective power : 0.6 kW
Pot capacity : 12 litres
Pot diameter : 28 cm
Max. temperature : 200C
Capacity : Boils 48 litre
of water in a day
Tracking : Manual
Cost : INR Rs. 6000/-
Cooking Food : people at a time

22. Seifert Parabolic Domestic Solar Cooker (SK 14)

23. Community Solar Cooker
Components
Primary Reflector
Secondary Reflector
Tracking Mechanism
Technical details
Primary reflector is 7 m2 parabolic dish fitted with a set of acrylic / glass mirrors.
Primary reflector reflect and concentrate the sunlight falling on the dish onto the secondary reflector.
Temperature of concentrated sunlight at focal point reaches to 350C
Cook meals for persons.

24. Technical Specifications of the Community Cooker at IIT Delhi
Reflector shape& material
Elliptic shape (a=3800 mm, b=2750 mm), acrylic mirror sheets (0.6 m x 0.6 m)
Reflector area
7.3 m2
Secondary reflector
Aluminium foil
Focal length
3m (along the polar axis)
Maximum height of system
4 m
Maximum width of system
3 m
Number of mirror facets 12
Material of constructions of mirror
Acrylic mirror sheets
Size of focal spot of main reflector at front aperture of chullah
Shape-Elliptical, D1=30cm, D2=20cm
Size of focal spot of after secondary reflector (at the bottom of the vessel)
Circular shape, D=12cm
Type of Tracking Device
Semi-automatic
Surface area of secondary reflector
0.36 m2
Reflectivity of mirrors of main concentrator
0.75
Reflectivity of secondary reflector
0.65

25. Principle of working of Scheffler Community Solar Cooker

26. World's Largest Solar Steam Cooking System at Tirupati, Andhra Pradesh
Location
Installed at the temple town of Tirumala, Andhra Pradesh with nearly 50 percent funding from MNES
System
Employs automatic tracking solar dish concentrators to convert water In to high pressure steam which Is used for cooking purpose* In the community kitchen.
Technical Details
Solar dish concentrators (106 Nos) with total reflector area of about 1000m2.
Modular in nature and consists of several units (parallel & series) connected to central pipe-line system.
Each dish consists of scheffler mirrors with an aperture area of 9.4 sq.m.
Generates 4,000 kg of steam per day at 180°C and 10 Kg/cm2.
Cook meals for around 15,000 persons per day.
The cooker saves about 1,20,000 litres of diesel per year.
The total cost of the system Is about Rs. 110 lakh.
Implementing Agency
Ministry of Non-Conventional Energy Sources (MNES).

27. WORLD’S LARGEST SOLAR STEAM COOKING SYSTEM AT TIRUPATI

28. SOLAR ENERGY CENTRE (SEC) TEST PROCEDURE
Two types of tests are carried out in India on all solar thermal devices including solar cookers. These are performance test and degradation test. Before conducting these tests, a third test namely the physical verification test is also done which is performed just after the cooker is received for getting it tested. Under this test, it is verified whether all the components have been supplied as per the specifications of MNRE/SEC or not. In case the specifications are not followed, the manufactured/nodal agency/marketing agency is informed about the deficiency alongwith the first performance test report and asked to follow the specifications.