solar cooker.

1. Welcome

2. Seminar on
Solar cookers
Presented by
Phadtare prajakta dinkar
Ph.D. Scholar

3. Content
 Introduction
 Cooking principle
 Classification
 Box type solar cooker
 Parabolic cooker
 Panel cooker
 Shefller dish
 Folding umbrella type solar cooker
 Cylindro parabolic type solar cooker
 Spiral reflector type solar cooker
 Vacum or evacuated type solar cooker
 Solar Steam Cooking System at Shri Saibaba Sansthan Trust, Shirdi,
MS, India

4. Introduction
Need of solar cooker
 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.
Contd….

5.  The burning of wood as fuel leads to massive
increases in deforestation and greenhouse gas
emissions.
 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.
 Hence need to harness the solar energy.

6. 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.
 The steps involved in the solar cooker are concentrating
capturing and converting the solar energy.
 Clean cooking technology.

7.  Concentrating sunlight: designed to achieve temperatures
of 150°F (65°C) (baking temperatures) to 750°F (400°C)
(grilling/searing temperatures) on a sunny day.
 Converting light energy to heat energy: Solar cookers
concentrate sunlight onto a receiver such as a cooking pan.
The interaction between the light energy and the receiver
material converts light to heat.
 Trapping heat energy: It is important to reduce convection
by isolating the air inside the cooker from the air outside the
cooker.

8. 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

10. Box type solar cooker

11. 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.

12. 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.

13.  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.

14.  Disadvantages
 One has to cook according to the sunshine, the menu has to
be pre-planned.
 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.

15. Parabolic cooker

16.  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.

17.  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.
Working

18. 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.

19. Panel cooker

20.  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

21.  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.
Working

22. Advantage
 Better performance than box cooker
Disadvantage
 Relies more on reflected radiation

23. Scheffler dishes

24.  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.

26.  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.
 Common applications where Scheffler steam systems are used
are:
 Boiler feed water preheating
 Oil heating for cooking or industrial applications
 Steam cooking

28. 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.

29.  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.
Disadvantages

30. Folding umbrella type solar cooker

31.  This is a lightweight portable parabolic cooker, based on an
umbrella.
 The model can be used year-round, but in winter, it is
necessary to cover the receptor with a high density polythene
bag (HDPE).
 A Polypropolyne bag can be used following the same cooking
instructions as for other classic cookers such as cookit.
 An umbrella (preferably a non-folding model in order to keep
the cooker in good condition)Reflective sheeting (aluminium
foil or similar)
 Metal support for the cooking pot

32. Cylindro-Parabolic type solar cooker

33.  The cylindro-parabolic concentrator focused the rays into an
insulated.
 Cylindrical box in which two or more cooking vessels could
be accommodated.
 Bowman, who built and tested the design, encountered several
difficulties (Bowman, Blatt 1978), and he tried to improve
upon the design.
 This resulted in a series of new concepts.almost similar to
Prata’s design but it has only a single cylindro-parabolic
swinging reflector.

34. Spiral reflector type solar cooker

35.  Design begins with a computer program that prints a spiral
pattern.
 This pattern is transferred onto a flat material already covered
with a reflective medium, then cut out on a band saw.
 By lining up mounting points (also printed by the program)
along a straight frame member, the proper twist is given to each
segment of the spiral to concentrate sunlight at the selected focal
point.
 The computer program can vary the focal length of the spiral or
even alter the design to focus light behind the reflector.

36. Vacuum or evacuated tube solar cooker

37.  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.
 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.

38.  The evacuated glass tube tube receives the solar rays that
pass through and is absorbed by the inner lining.

39.  The combination of the highly
efficient absorber coating and
the vacuum insulation means
that the coating can be well over
200oC.
 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.

40. Solar Steam Cooking System at Shri Saibaba
Sansthan Trust, Shirdi, MS, India
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.

41. A Scheffler type concentrating solar steam cooking system
was commissioned at Shri Saibaba Sansthan, Shirdi on 30th
July, 2009.
It cooks food for about 3000 devotees.
The 73 nos. of solar Scheffler concentrators raise the water
temperature to 550oC to 650oC and convert it into steam for
cooking purposes.
This system is integrated with the existing boiler to ensure
continued cooking even at night and during rainy or cloudy
weather.

42. The solar cooking system installed at Shirdi follows the
thermosyphon principle and so does not need electrical power or
pump.
73 parabolic concentrators / dishes placed on the terrace of Sai
Prasad Building No.2.
They reflect and concentrate the solar rays on the 40 receivers
placed in focus.
Water coming from the steam headers placed above the header
centers is received from bottom of the receiver, gets heated up to
5500C due to concentration of solar rays on the receivers and get
pushed up via top pipe of receiver into the header.

43. The principle of anything that gets heated is pushed up is called
thermosyphon principle.
The advantage of thermosyphon principle is no pumping (thus no
electricity) is needed to create circulation since the heated water
is pushed into the header and water from the same headers come
into the receivers for heating.
The cycle continues till it reaches 100 0C and gets converted into
steam.
Only once during the day i.e. in the early morning the dishes
have to be turned manually onto the morning position,
subsequently the automatic tracking takes over.

44. Schematic view of system installed at Sai Baba Sansthan`s
Prasadalaya, Shirdi

46. Design Specification of box type solar
cooker
 Outer box, (600 X 600 X 200 mm)
 Inner cooker box, aluminium sheet of 1 mm,
(460 X 460 mm top face and 300 X 300 mm bottom faces
with face depth of 150 mm
 Glazing (double), ordinary glass sheets of 4 mm,
insulation-fibre glass,
 Reflectors (mirrors), silvered glass mirror of 2 mm,
600 X 600 mm
 Cooking pot, 300 X 300 mm, with dull black paint and

47. Design consideration
 Concentration ratio (CR)
 Overall instantaneous insolation (IT)
 Collector tilt
 First figure of merit (F1)
 Second figure of merit (F2)
 Internal cooking power (P)
 Standard cooking power (Ps)
 Temperature difference (Td)
 Aperture area

48. Structure of box type cooker

49. Performance Testing
I. Concentration ratio (CR) =
Where,
At = total collector area
Arc = area of the receiver / absorber surface
II. Overall Instataneous Insolation (IT) = Ib + Id + Ir
Where,
Ib = Beam radiation
Id = Diffused radiation
Ir = Beam insolation reflected on the reflector
surface

50. III. First figure of merit (F1) =
where,
F1= first figure of merit Km2w1
ή = optical efficiency (%)
U
L
= Overall heat loss
T
p
= Absorber plate temperature (℃)
T
a
= ambient temperature (℃)
I
s
= Insulation (Wm -2)

51. IV. Second figure of Merit (F2)=
Where,
M= mass of water (kg)
C= Specific Heat (J/Kg ℃
V. Interval Cooking Power (P) =
VI. Standard cooking power(Ps) =
VII. Temperature Difference (Td) = Tw - Ta

52. Design of concentrator cooker
1.Required Power for Cooking (Qr):
Qr =
𝑚Cp ΔT 𝑤+ 𝑚CpΔT 𝑟
600
Where,
Qr = Required power for cooking (kcal)
M = Mass of water and rice (Kg)
Cp = Specific heat capacity (Kcal/Kg K)
ΔT =Temperature difference (Tf-Ti)(k)

53. 2. Selection of parabolic aperture and focal length:
Qd = Qf * τ * α * ϕ
Where,
Qd = Energy delivered by paraboloid (kcal)
Qf = Average energy falling at Dapoli (kcal)
τ = Specular reflectance of reflector
α = Absorptance of absorber(greater than 0.98)
ϕ = Intercept factor
silver/glass mirrors can have a reflectance of 0.94 and aluminum reflecting
surfaces have a reflectance of about 0.86.
3. Aperture diameter calculation:
Qr = Qd *
𝜋
4
𝐷
2
Where,
Qr = Energy required for cooking (kcal)
D = Aperture diameter of paraboloid (m)

54. 4. Conventional losses:
Qconv = hc* A(Tr - Ta)
Where,
Qconv = Heat transfer rate by convection(W)
hc = Convective heat transfer coeff.(W/m2K)
A = Area of receiver(m2)
Tr = Surface temperature of receiver(K)
Ta = Temperature of the air(K)
5. Radiation losses:
Qrad = A* σ * (ΔT)4
Where,
σ = Stefan-Boltzmann constant (5.670 × 10-8 W/m2 K4)
Tr = Surface temperature of receiver(K)

55. 6. Focal length calculation:
4f Z =
𝑋2+𝑌2
2
Where,
X = X co- ordinate of parabola
Y = co- ordinate of parabola
f = Focal length of parabola (m)
Z = Depth of paraboloid (m)
7. Rim angle of the paraboloid:
tan ϕ =
1
𝑑
8ℎ
−
2ℎ
𝑑
Where,
d = Diameter of dish
h = Height of dish

57. 8. Surface area of paraboloid:
A =
8×𝜋×𝑓×𝑓
3
𝑑
4×f
2
+ 1
3/2
− 1
Where,
A = Surface area of paraboloid(m2)
f = Focal length(m)
9. Concentration ratio:
C =
Aa
Ar
Where,
Aa = Area of aperture(m2)
Ar = Area of receiver(m2)

58. 10. Efficiency of solar concentrating collector:
η =
𝑀𝑤 × 𝐶𝑤 + 𝑀𝑝𝑜𝑡 × 𝐶𝑝𝑜𝑡 𝑇𝑤𝑓− 𝑇𝑤𝑖
𝐴𝑝𝑎𝑟𝑎𝑏𝑜𝑙𝑒 × 0
1
𝐼𝑏 𝑑𝑡
× 100
Where,
Twf = Final temperature of water(°C)
Twi = Initial temperature of water(°C)
Mw = Mass of water(litter)
Cw = Specific heat of water(KJ/Kg K)
11. Thermal losses factor:
FʹUL =
(M ×C)𝑤
Apot × τo
Where,
FʹUL = Thermal losses factor
Mw = Mass of water(litter)
Cw = Specific heat of water(KJ/Kg K)
Apot = Area of pot (m2)
τo = Sensible cooling constant

59. 12. Optical efficiency factor:
F’η =
𝐹′ 𝑈𝐿 𝐴𝑝𝑜𝑡
𝐴𝑝𝑎𝑟𝑎𝑏𝑜𝑙𝑒
𝑇𝑤𝑓− 𝑇𝑎
𝐼𝑏
−
𝑇𝑤𝑖−𝑇𝑎
𝐼𝑏
𝑒−𝜏/𝜏𝑜
1−𝑒 𝜏/𝜏𝑜
Where,
τ = Duration of interval(eg.10 min or 600s )
13. Thermal efficiency:
Thermal efficiency(ηt) =
𝐻𝑒𝑎𝑡 𝑈𝑡𝑖𝑙𝑖𝑧𝑒𝑑
𝐻𝑒𝑎𝑡 𝑃𝑟𝑜𝑑𝑢𝑐𝑒𝑑
∗ 100
Where,
ηt = Thermal efficiency of parabolic cooker (%)

60. Components and Material selection
 Reflecting surface: made of single/ multiple reflectors
 Concentrating Reflector: Anodized aluminum sheet/ glass
mirrors/ aluminum foil/ any other better and durable material
with protective layers of coating on back surface and sides.
 Supporting frame of the dish: made of MS rings supported by
MS strips
 Bowl stand: mild steel
 Cooking pot: ISI mark pressure cooker of 2 to 5 lit capacity
 Tracking mechanism: Manual or automatic