Classification of solar cooker and Calculations of energy required for cooking

1. SEMINAR PRESENTATION
ON
SOLAR COOKER
Session:2018-2019
Presented by: Presented to:
Maga Ram Patel Dr. Surendra Kothari
DEPARTMENT OF RENEWABLE ENERGY ENGINEERING
College of Technology and Engineering
Maharana Pratap University of Agriculture and Technology
Udaipur - 313001

2. NEED FOR SOLAR COOKING
 Major portion of total energy consumed in cooking.
Half the word’s population burn wood or dried dung
to cook food.
In village, 95% energy consumed for cooking.
 Source of fuel used for cooking
- coal, kerosene, cooking gas
- firewood, dung etc.
 People are exposed to indoor air pollution as a result
of burning solid fuels for cooking and heating.
 Millions of people can’t find enough wood to cooking,
so using solar cookers is a good idea.
 Therefore need to harness the solar energy.

3. OVERVIEW:
 Cooking Principle
 Classification of Solar cookers
 Commonly used Solar cookers
 Calculations

4. COOKING PRINCIPLE
 Solar cookers are passive solar
devices.
 Sunlight is converted to heat energy
which is retained for cooking.
 Solar cookers utilizes 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 Types Cooker
 Panel Types Cooker
(Multi reflector type)
 Parabolic Types Cooker

7. SOLAR BOX COOKER
 Most common and inexpensive
type of solar cookers.
 Employs greenhouse effect.
 Most popular and easier to
build.
 Typical model : 60 x 60 x 20 cm
 Reach temperature up to 140-
150 ⁰C.
 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.
 The solar rays penetrate
through the glass covers and
absorbed by a blackened
metal tray kept inside the
solar box.
 To maximize the heating
effect, the walls and outer
side of the pots should are
painted black.

9.  The solar rays entering the box are of short wave
length, it degrades into thermal radiation which are
of higher wave length.
 The higher wave length radiation is not able to pass
through the glass sheet.
 The upper cover of the cooker has two glass sheets
in parallel and thus heat loss through re-radiation is
minimized from the blackened surface.
 The loss due to convection is minimized by making
the box air tight by providing a rubber strip all round
between the upper lid and the box.

10. ADVANTAGES:
 There is no problem of charring of food and no over
flowing.
 Orientation or sun tracking is not needed.
 No, attention needed during cooking as in other devices.
 No , fuel, maintenance or recurring cost.
 Simple to use and easy to manufacture.
 No pollution of utensils, house or atmosphere.
 Vitamins in the food are not destroyed and food cooked
is nutritive and delicious with natural taste.
 One can relay on cooker’s efficiency for longer period.

11. DISADVANTAGE:
 One has to cook according to the sunshine, the
menu has to be preplanned.
 One can not cook at short notice and food can not
be cooked in night or over, cloudy days.
 It takes comparatively more time.
 Chapaties are not cooked because high
temperature for baking required and also needs
manipulation at the time of baking.

12. PARABOLIC COOKER:
 Parabolic type solar cooker
developed by National Physical
Laboratory (NPL) of India at New
Delhi as early as 1955.
 Focus a lot of sun energy onto a
very small space, using parabolic
shapes.
 Reach temperature up to 450 ⁰C.
 Works on the principle that when
a 3D parabola is aimed at sun,
the rays are reflected on to the
focus.

13.  Consists of a large parabolic 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 surface are blacked to
improve the absorption.

14. Advantages:
 Cooks nearly as fast as a conventional oven.
 High temperatures of the order 450 °C of allow for
food to be fried and grilled.
Disadvantages:
 Costly and complicated to make and use have to
turn frequently to follow the sun.
 Generally more expensive than panel and box
cookers.
 Housewife has to cook the food out of doors in the
sun hence it is not favoured.

15. PANEL COOKER:
 Cooking pot is enclosed by a panel of reflectors.
 Eight reflectors made of silvered glass mirrors, four of
square shape (35x35x0.3) and four of tringular shape
(35,25,0.2x0.3).
 Sunlight is reflected off of multiple panel 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

16. 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 insulting shell such as high
temperature cooking bag or an inverted bowl.
 On very clear days, maximum plate temperature in the
oven reaches to 350⁰C and 250 ⁰C in winter season.
 Practically all types of food preparations like cooking ,
Roasting, Baking and Boiling can be done within 25 to 75
minutes under clear sky conditions.
 The Bati (a local preparation, generally in Rajasthan and
M.P. ) can be prepared in this oven.

17. 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 Aluminum 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.

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

19.  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.

20.  The Sai Baba temple complex at
Shirdi, Maharastra’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.

21. 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

22. 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.

23. ENERGY REQUIRED FOR COOKING
 The energy required for cooking a specified food varies with
the properties of ingredients such as water, vegetables etc.
The method cooking such as the temperature required for
cooking, minimum temperature to be maintained during
cooking, duration of temperature maintenance etc. are to be
considered at the time of cooking.
 Thermal energy required for reaching the cooking
temperature can be calculated from the following formula.
Q = mcpdt, kJ
Where,
Q = Thermal energy requirement for cooking, kJ
m = mass of material taken for cooking, kg
cp = specific energy for the selected material, kJ kg-1°C1
dt = difference between initial and final temperature, °C

24.  The specific heat energy of various materials are given below.

25. Example: Calculation of energy requirement for cooking 1 kg of
rice. Consider cooking of rice in Aluminium vessel weighing
about 0.5 kg. Water used for cooking rice is 2 kg. The required
heat energy is the sum of thermal energy required for heating
rice, water and also the vessel material. The initial ambient
temperature is 30°C and the required cooking temperature is
100°C.
Solution :
Total thermal energy required for cooking rice
= (m1cp1 + m2cp2 + mcp3) x dt
Where suffix 1 for rice, 2 for water and 3 for vessel
material
Hence the total energy is calculated as
={(1 x 3.8) + (2 x 4.18) + (0.5 x0.9)} x (100-30)=882.7 kJ
To maintain the same temperature for through cooking, let us
assume 30% of energy is required through out the period of
cooking.
Total heat energy requirement = 882.7 x 1.3 = 1147.51 kJ

26. CALCULATIONS
A parabolic solar cooker has a parabolic collector with AIn=5Arec
and Y=0.8 . The average intensity is Iav = 700W/m2 and Heat
loss coefficient, U= 40 W/m2◦c . Assuming properties of water
for the food being cooked, calculated the time required to
cook 2 kg of food using the cooker. Given 𝞰th= 0.4 .
Solution:
AIn, Area of the incident solar radiation(m2) = 2m2
Arec, Area of the receiver (m2) = 0.4 m2
Y, Optical Efficiency = 0.8
Iin, Incident solar irradiation (W/m2)= 700W/m2
Ta, Ambient temperature (◦c) =25◦c
U , Heat loss coefficient (W/m2K) = 40 W/m2◦c
𝞰th , Thermal efficiency = 0.4

27. ▲T = (Y*Ain*Iav)/(U*Arec)
▲T= (0.8*2*700)/(40*0.4) = 70◦c
𝞰=(M*Cp*▲T) / (Iav*Ain*t)
Assuming Cp = 4180KJ/Kg
0.4=(2*4180*70)/(700*2*t)
Time, t= (2*4180*70)/(0.4*700*2)= 1045s
So the time required for cooking is 1045s

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