Document Sample
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
  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
• 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.
            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.
    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
       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.
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
Direct (focusing) type solar cookers
  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.
  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
Box type Solar Cookers
   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.
  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
A Few Advanced Type Solar Cookers
 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.
Box type Solar Cooker
             Solar Box – type Cooker : Design Details
Component          Material              Thickness / size         Requirements / Remarks
Outer Box          (i)Galvanished iron   0.48 mm thick            Resistant to ultraviolet
                   (ii)Aluminium         (60 x 60 x 17 cm)        radiation and atmospheric
                   (iii)FRP              0.56 mm thick            variations
                                         (60 x 60 x 17 cm)
                                         2 mm thick
                                         (60 x 60 x 17 cm)
Inner Cooking      Aluminium             0.56 mm thick            Painted dull black
Box                                      (50 x 50 x 10 cm)        Should not touch outer body
Insulation (Back   Glass fibres in the   5 cm or more thick       Free from resin binders Stable
and side)          form of pads          k = 0.052 W/m K          upto 250C
Glazing (Double    Water white glass     3-4 mm thick             Double glass system must be
glass lid)         (Temperated /         50 x 50 cm size          air tight
                   toughned)             spacing between sheets   Transmittance > 85%
                                         1 cm
Reflectors         Silvered or           4 mm thick               Reflectivity > 85%
(Mirrors)          Glass aluminized      54 x 54 cm               Scratch resistant
                                                                  Resistant to solar radiation
                                                                  and atmospheric variation
Cooking            (i)Aluminium alloy    1.2 mm thick             Dull black painted stable upto
Containers         sheet                 Two pots – dia 200 m     250C
                   (ii)Stainless Steel   Two pots – dia 150 mm    Very good adhesive
                   sheet                 Depth of pots – 67 mm    characteristics
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:
  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
• 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.
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              :   10-15 people at a time
Seifert Parabolic Domestic Solar Cooker (SK 14)
     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 60-80 persons.
    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                  4m
Maximum width of system                   3m
Number of mirror facets                   12
Material of constructions of mirror       Acrylic mirror sheets
Size of focal spot of main reflector at   Shape-Elliptical, D1=30cm, D2=20cm
front aperture of chullah
Size of focal spot of after secondary     Circular shape, D=12cm
reflector (at the bottom of the vessel)
Type of Tracking Device                   Semi-automatic
Surface area of secondary reflector       0.36 m2
Reflectivity of mirrors of main           0.75
Reflectivity of secondary reflector       0.65
Principle of working of Scheffler Community Solar Cooker
    World's Largest Solar Steam Cooking System at
               Tirupati, Andhra Pradesh
• Installed at the temple town of Tirumala, Andhra Pradesh with nearly
   50 percent funding from MNES
• 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
• 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
• 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).
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
              PROCEDURE (contd.)
Two types of tests are carried to evaluate the
performance of the cooker. These are:

I) No Load Test - The cooker is kept in the sun with empty cooking pots inside
and its temperature profile along with solar insolation and ambient temperature
is recorded. Simultaneously, temperature profile is also recorded for cooker
fabricated at SEC as per the specifications. If the profile of the cooker under
test is not less than 5°C of the cooker fabricated at SEC, the cooker under test
is passed. For a solar insolation of 600 Watts/m2, the temperature should not
be less than 120°C, provided that the SEC cooker is able to attain 125°C under
the same conditions.

II) Load Test - 2 kg of water is distributed in four cooking pots and kept inside
the cooker. The temperature profile along with solar insolation and ambient
temperature is recorded for both the cookers. The maximum temperature in this
case should not be less than 100°C for a solar insolation of 600 Watts/m2.
Temperature profile of the cooker under test should not be less than 5° of that
for the cooker fabricated at SEC.
            PROCEDURE (contd.)

• A minimum of 30 clear sunny days are required to
  complete the degradation test. The cooker is kept in the
  sun with empty cooking pots inside and degradation, if
  any, of various components is studied carefully. There
  should not be any degassing from insulating material,
  sealing gaskets, paints etc. collection of water vapours
  within the space between the glasses of the lid, the
  change in colour of the cooking pots, tray, cooker box
  etc., observed and deposition of water vapours or any
  other material on the glass lid (both inside and outside)
  on exposing the cooker to outside atmospheric
  conditions in the sun is not permitted. Cookers showing
  such degradation are not allowed to be sold under the
  subsidy scheme.
                 PROCEDURE (contd.)
NOTE: All the manufacturers / suppliers are required to give a guarantee card
along with instruction manual. The guarantee card should read as:

The solar cooker manufactured and supplied by M/s ......... ..... ..... ...... ...
....................... (complete address) is guaranteed for a period of two
years against any manufacturing defect, use of inferior        quality   materials
and         poor worksmanship        including    improper silvering/aluminising of
reflecting surface etc. The breakage of glass components is, however, not
covered under this guarantee.

•Name of the manufacturer...................

•Full Address and.........................
•Telephone No. ..................................
•Name of purchaser ..............................
•Full Address and ................................
•Telephone No. ...................................
•Cooker No. .......................................
•Date of Sale ....................................

Signatures: (1) Supplier                                (2) Purchaser
“When you really want something to happen, the whole
universe conspires to help you to achieve your dreams”
                                …….. The Alchemist
                                 by Paulo Coelho

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