Classification and Working of different types of solar cookers . Solar cooker is a promising technology in this era of energy crisis

1. SOLAR COOKER
1
Dept. Of Mechanical Engineering
IIT Madras

2. NEED FOR SOLAR COOKER
• Half the world’s population burn wood or dried dung to cook food.
• Wood cut for cooking purposes contributes to the 16 million hectares of
forest destroyed annually.
• People are exposed to indoor air pollution as a result of burning solid
fuels for cooking and heating.
• Nearly 1.2 billion people, do not have access to clean drinking water.
• Over 1 million children die yearly because of un-boiled drinking water.

3. OVERVIEW
• Cooking Principle
• Classification of Solar cookers
• Commonly used Solar cookers.
• Vacuum Tube Solar cookers
• Community solar cooking
• Thermal storage solar cooker
• Calculations

4. COOKING PRINCIPLE
• Solar cookers are passive solar devices.
• Sunlight is converted to heat energy which is retained
for cooking.
• Solar cookers utilize the simple principles of reflection,
concentration, absorption and greenhouse effect to
convert sunlight to heat energy.
• The steps involved in the solar cooker are concentrating
, capturing and converting the solar energy.
• Clean cooking technology

5. CLASSIFICATION
1. Direct Type : Use some solar energy concentrator to focus sunlight onto an
area.
Eg: Parabolic solar cooker
2. Indirect Type: A box covered with transparent material like glass. Employs
greenhouse effect for cooking
Eg: Solar box cooker
3. Advanced Type: The cookers use either a flat piece or focusing collector,
which collect the solar heat and transfer this to the cooking vessel.
Eg: Thermal storage solar cooker

6. Common Types Of Solar Cookers
• Box Cooker
• Panel Cooker
• Parabolic Cooker

7. Solar Box cooker
• Most common and inexpensive type of solar
cookers.
• Employs greenhouse effect.
• Most popular and easier to build.
• Reach temperatures up to 140 – 150 oC
• Advantage of slow, even cooking of large
quantities of food.

8. WORKING
• Consists of an insulated box with a glass or
a plastic window.
• The window acts as a solar energy trap by
exploiting the greenhouse effect.
• Solar radiation passes through the window,
and is absorbed by the walls, the bottom of
the cooker and the cooking utensils.
• To maximise the heating effect, the walls,
and outer side of the pots should are
painted black

9. Parabolic Cooker
• Focus a lot of sun energy onto a very small
space, using parabolic shapes .
• Works on the principle that when a 3D parabola
is aimed at sun , the rays are reflected on to the
focus.
• Cooks nearly as fast as a conventional oven
• Costly and complicated to make and use –
have to turn frequently to follow the sun

10. • Consists of a large parabolic reflector and cooking
pot holder
• When the reflector surface is aimed at the sun , the
rays falling on the parabolic surface converges to
the focus of the parabola.
• The cooking pot is placed at the focus of the
reflector.
• The pot surfaces are blacked to improve the
absorption.

11. Panel Cooker
• Cooking pot is enclosed by a panel of
reflectors.
• Sunlight is reflected off of multiple panels onto
a pot under a glass lid or in a bag .
• Can be built quickly and at low cost
• Many different varieties
• Popular with relief agencies.

12. WORKING
• It incorporates elements of both parabolic and
box solar cookers.
• The reflective panel directs sunlight onto a
dark colored pot.
• The pot is enclosed in an insulating shell such
as high temperature cooking bag or an
inverted bowl.
• Can attain temperatures in the range of 95 –
125 oC.

13. TYPE ADVANTAGES DISADVANTAGES
SOLAR BOX COOKER
USE BOTH DIRECT AND DIFFUSE
RADIATION
EASY AND SAFE TO USE
REQUIRE LITTLE INTERVENTION BY
USER
HIGH ACCEPTANCE ANGLE
WIDELY DIVERGENT THERMAL
PERFORMANCE
PANEL COOKER BETTER PERFORMANCE THAN BOX
COOKER
RELIES MORE ON REFLECTED
RADIATION
PARABOLIC COOKER
CAN ACHIEVE HIGHER
TEMPERATURES.
HIGH EFFICIENCY
SAFETY PROBLEMS
CONSTRUCTION IS RELATIVELY
DIFFICULT
LOW ACCEPTANCE ANGLE
REQUIRES USER ATTENTION

14. VACCUM OR EVACUATED TUBE SOLAR
COOKER
• The design is a simple flat plate collector
housed in an evacuated glass tube
• The tubes are made from a type of glass
called Borosilicate, which is resistant to
thermal shock
• Borosilicate glass has the characteristic of
being very strong and also has excellent
light transparency.

15. • It consists of two concentric glass tubes with
vacuum in between.
• The outer tube is transparent while the inner
is coated with Aluminium nitride for better
absorption.
• The evacuated glass tube tube receives the
solar rays that pass through and is
absorbed by the inner lining.

16. • The combination of the highly efficient
absorber coating and the vacuum
insulation means that the coating can be
well over 200o C.
• Due to the presence of vacuum , the heat
losses will be negligible
• A reflector is provided for concentrating
sunlight onto the tubes.
• A tray is provided inside the glass tube for
cooking purposes.

17. Community Solar Cooker
• Cook using solar energy within the kitchen
itself.
• Due to high temperature and power at focal
point, the cooking rate is significantly higher.
• Cooking for about 40 to 50 persons is possible
with 7 sq. m,. size dish cooker.
• The most popular version is the scheffler
community kitchen.

18. HELIOSTAT
• A device that reflects sunlight in a fixed direction as
the sun moves is known as a Heliostat.
• The heliostats are mirrors with solar tracking on
two axes and capable of concentrating the
reflected solar radiation on a focal point.
• Heliostats are generally made from iron glass
• Scheffler heliostats are used for community solar
cookers.

19. SCHEFFLER DISHES
• A Scheffler reflector is a small lateral section of a paraboloid
which concentrates sun’s radiation over a fixed focus.
• The collector of Scheffler Dish is an assembly of flat shaped
solar grade glass mirrors or Aluminium mirror reflectors
arranged on a structural steel framework.
• The receiver of scheffler dish is placed at the focus of the
dish to capture the incident solar radiation and transfer it to
the thermal medium.
• Tracking system enables the dish to be focused towards the
sun to capture maximum possible direct radiation during the
day.

20. Some of the common application where Scheffler steam systems are used are:
• Boiler feed water preheating
• Oil heating for cooking or industrial applications
• Steam cooking

21. Principle of working of Community Solar
Cooker
• Consists of heliostat and secondary
reflector.
• Heliostat concentrates the beam on
to the secondary reflector which
focuses it on to the bottom of pot.
• When not cooking the energy can
be used for heating water or can be
stored.

22. • The Sai Baba temple complex at Shirdi, Maharashtra’s
Ahmednagar district, has installed one of the world’s largest
solar cooking system based on schfeller dishes.
• The solar rays are used to heat up water to generate steam
which is directed through pipes in to steam cookers to cook
food
• The steam cooked food along with food cooked with LPG is
enough to feed 50,000 persons a day. The system saves
242kg of cooking gas

23. Stored Energy Solar Cooker
• The major drawback of solar cooker is that cooking cannot be done
when solar energy decreases.
• Stored energy solar cooker stores the reflected solar energy to be
used when sunlight is not available.
• It is an advanced type solar cooker.
• PCM’s ( phase change materials) which have high latent heat are
usually used for storage of energy.

24. THERMAL STORAGE
Two methods are available for storage of thermal energy
1. Sensible heat storage : Energy is stored or extracted by heating or
cooling a liquid or solid without change in phase. The choice of substance
depends on the temperature range. Water is used for temperatures below
100 c and refractory bricks for temperatures around 1000 c . These are
simpler in design compared to latent heat storage systems but they are
bulky in size. Also they cannot provide heat at a constant temperature

25. 2. Latent heat storage: They store heat by change
of phase of material. Due to the phase change
they can store large amount of heat at a constant
temperature. A PCM(phase change material) is
used for storage of heat energy. Unlike the SHS
method, the LHS method provides much higher
storage density, with a smaller temperature
difference between storing and releasing heat.

26. • Solar rays penetrate through the glass covers
and absorbed by copper tubes.
• The other end of the copper tubes is
connected to storage tank.
• The storage tank contains a refrigerant .
Refrigerant absorbs the energy from the
tubes and stores it into a tube of containing
PCM.
• This stored energy is used to maintain the
temperature of the cooker when the sunlight
is not available.
WORKING

27. CALCULATIONS
A parabolic solar cooker has a parabolic collector with Ain = 5 Arec and γ = 0.8 . The
average intensity of radiation is Iav = 700 W/m2.and Heat loss coefficient , U = 40 W/m2 .
Assuming properties of water for the food being cooked , calculate the time required to
cook 2 kg of food using the cooker . Given ηth = .4 .
Ain , Area of the incident solar radiation (m2) = 2 m2
Arec , Area of the receiver (m2) = 0.4 m2
γ , Optical Efficiency = 0.8
qin , Incident solar irradiation (W/m2) = 700 W/m2
Ta , Ambient temperature (°C) = 25 o C
U ,Heat loss coefficient (W/m2K) = 40 W/m2
ηth ,Thermal efficiency = 0.4

28. ΔT = ( γ * Ain * Iav ) / (U* Arec )
ΔT = (0.8*5*700) / 40 = 70 0 C
η = (M * Cp * ΔT ) / (Iav * Ain * t )
Assuming Cp = 4180 KJ/Kg
0.4 = (2*4180*70)/(700* *t)
Time , t = (2*4180*70)/(.4*700* 2 ) = 1045 s
So the time required for cooking is 1045 s

29. ADVANTAGES
• It is a renewable energy
• The solar cooker requires neither fuel
• it preserves more of the natural nutrients of the foods by cooking at slower and
lower temperatures
• Saves a lot of firewood
• Can be used in areas where fuel and firewood are not available

30. DISADVANTAGES
• It is not continuous.
• It cannot be used during rainy season or cloudy
conditions.
• Performance could be affected by strong winds
• Time required is higher than conventional
cooking methods.

31. “I’d put my money on the sun and solar energy. What
a source of power! I hope we don’t have to wait ‘til oil
and coal run out before we tackle that”.
Thomas Edison
THANK YOU