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It is interesting to
note that attempts to select the best design have been made since the 1960s but
the best design is still elusive. Another fact is that almost all the past
reviewers have observed that the existing designs were not up to the mark and
found it FIT to propose new designs. In fact, this review is also not an
exception, and the author has taken the liberty of presenting almost 12 new
designs or variations. So the list could go on and render decision-making
difficult for the interested public.
In 1961, VITA brought
out a very detailed review. This was indeed a landmark review, and formed the
basis of this research work at Udupi. There were also several other reviews
like those of Gupta (1975) , Garg (1978), GATE Group (GATE 1979), Bowman, Blatt
(1978), and many more (Habeebullah, Khalifa, Olwi 1995; Khalifa, Taha, Akurt
1985) on the subject. Some of the reviewers concentrated on the marketability,
like why the solar cookers are not so popular, etc., and among such reviews
that of GEDA (1979) and the more recent review of Wentzel (1966) are of
importance. Recently the team led by Dr. Paul A Funk has formulated an
International Standard for testing of Solart Cooker. I have included the
details as per his directions, the details could be found if you click
here.
Evaluation
of cookers
To start with, one has
to concentrate on the performance evaluation and cost of the cookers. Many
parameters have been considered and, at best, one can only summarize these
findings.
VITA (1961) considered
eight parameters to judge a cooker and they are : (I) cooking performance, (ii)
durability, (iii) cost, (iv) weight, (v) portability, (vi) ease of operation,
(vii) ease of manufacture, and lastly, (viii) adaptability to local skills and
materials. After detailed reasoning they found none of the designs that existed
came up to mark and were obliged to present three new designs. Walton et al.
(1977) conducted another survey of the state-of-the-art; they built and tested
seven types of cookers and concluded that none were up to the mark. Of the lot,
they recommended three types, but the best design according to them was the
reflector type.
Bowman (1978) presented
another detailed review. He evaluated the cookers on the basis of 15 points (Table
1). They were:
- Time to
boil measured amount of water (10)
- Maximum
temperature of measured amount of oil (10)
- Energy
storage (10)
- Cooking
capacity (10)
- Versatility (10)
- Other
measurers of cooking effectiveness (5)
- Ease of
use (10)
- Ease of
maintenance (5)
- Durability (5)
- Wind
stability (10)
- Portability (10)
- Material cost (10)
- Imported items (10)
- Ease of
manufacture (10)
- Transportability (10)
Figures in the
parentheses represent the weightage given to each parameter. Prof. Bowman
admits that the parameters selected have a Haitian bias, and hence, are a bit
arbitrary, so he feels that solar scientists should evolve a standard set of
parameters for testing a cooker. ( Author feel that, care should be taken that
an ordinary woodstove or a liquefied petroleum gas stove should not ‘fail’ when
subjected to such a test, in other words, such conventional stoves should form
the basis of comparison for solar stoves as well). Prof. Bowman tested about
eight designs. Out of a total of 140 marks (Table 1) he allocates 91 for the
Wisconcin parabolic cooker, 85 to Telkes Halacy, and 66 to the Brace Research
Wisconcin parabolic cooker, 96 to Telkes, and 56 to the Brace Research Cooker.
He evidently did not find a good design and was compelled to present the FIT
concept like Type MP 3. For people who prefer the Telkes type of box cooker he
modified it too and made it more efficient (Type BFF 1d) The new cooker with
foam glass insulation could heat oil up to 200 C and boil 1 lit of water in 45
minutes. The author of the current review has made some more alterations to
this design (Type BFF 1 e) but the tests did not show any improvement.
Lof (1963) did some
analysis of solar cookers using computers. He has incorporated data of tests
conducted by the Food and Agricultural Organization. In his compilation, he
presents tests and specifications of about 10 solar cookers of which two were
proposed but evidently not fabricated designs. The charts present the data but
it is difficult to compare and select. But the scale tilts in favor of focusing
the parabolic type cooker.
Next on the list is the
very methodical survey conducted by GATE (1979). They have compiled data on 16
cookers. In future, all the cookers are to be tested as per the pattern laid
down by them. Three broad categories under which they consider the cookers are:
construction (under which 10 points are tested), efficiency (15 points), and
handling and costs (5 points). Together 30 points are considered. Quantitative
as well as qualitative values are allocated (Table 2).
Table 1. Evaluation of
seven cookers
Name of cookers
|
Wiscon-
Cin*
|
Solar
Chef
|
Skewer
Type
|
Collapsible
parabola
|
Telkes
Oven*
|
Telkes
Halacy’s
|
Brace
cooker
|
|
Code in this Review
|
MP
1a
|
CP
2
|
PC
1 c
|
BFF
1
|
BFM
1
|
IDT
1 a
|
||
Characteristics
|
Points
|
|||||||
Time to boil water
Maximum temperature
Energy storage
Capacity
Versatility
Effectiveness
Ease of use
Ease of maintenance
Durability
Wind stability
Portability
Material cost
Cost of imported
Items
Ease of manufacture
Transportability
Total
score
|
10
10
10
10
10
5
10
10
5
10
10
10
10
10
10
140
|
10
10
0
5
5
5
7
2
2
7
10
4
8
7
9
91
|
5
3
1
2
5
1
5
5
4
8
10
8
9
5
4
75
|
0
0
0
0
0
0
10
5
3
0
10
10
10
9
10
67
|
0
0
0
1
0
0
2
0
0
0
10
9
10
4
10
56
|
4
9
10
10
6
5
10
7
5
7
10
6
9
5
3
106
|
4
8
3
10
6
5
7
4
1
1
10
7
9
5
5
85
|
0
2
0
3
0
0
10
3
2
10
10
8
7
5
6
66
|
Source. Bowman, Blatt (1978) (Style of the table has been altered slightly)
• Based on previously
published results.
Table 2 is very
illustrative and useful. The design adjudged as the best, or which got maximum
marks was the Stam type which scores 67 marks, next was Von Oppen design with
66 marks. Sobaco got 48, Chinese asymmetrical scored 60, and so on. But some of
the other promising designs, like that of FIT concept OF Bowman, do not find a
place here, mainly because they were new. Interestingly, the Sobaco design gets
low marks. The group also evaluates the cookers on the basis of regional
characteristics, such as solar insulation, local requirements, and preferences
(Table 3).
Their analysis
recommends Von Oppen type cooker (Type PRD 1 in this review) for India (261
marks) whereas the box – type cooker (type BWM 1a) gets only 204 marks. For
Kenya the best suited cooker would be the steam cooker (Type IDT 1d) with 291
marks. For China the best cooker would be Chinese type (Type IDT 1d) with 291
marks. For China the best cooker would be Chinese type (Type PRA 2). Not
satisfied with any cooker, they fabricated a new type of parabolic cooker
designated here as Type PRD 2.
In recommending this
design the group lists the following advantages:
- A
reflector type cooker is chosen, because it is
applicable to several countries,
- Shortcomings of present cookers are minimized,
- The
vessel holder must be stable, it should not be
higher than 85 cm from the ground and should be suitable for different
type of pots.
Selection
of best design
continued
Table 2.
Evaluation of
solar cookers according to characteristics ( I Part )
Name of the
cookers
|
Von oppen
|
Box type
|
Garg type
|
Four mirror
|
||||
Code
|
PRD1
|
BWM1
|
BSM 1d
|
BFF1
|
||||
Construction
Principle
Radiation
Dimension
Aperture (m3)
Focal length
Intensification
factor
Reflector material
Weight (kg)
Stability
Portaility
*****
Efficiency
Effective power (w)
Degree of
efficiency
Max. temperature (oC)
Cooking cap. (Kg)
Number of pots
Cooking hrs. (Hrs)
Keeping warm (hrs)
Roasting?
Baking?
Access to food ?
Stirring?
Repositioning?
How often?
Stray light
General handling
*****
Production
Complicated?
Duration (years)
Local materials
Costs (US $)
Power costs (w/US%)
Total
|
-
Reflector
Direct
0.9x0.9x0.6
0.7
0.1
-
Alu. Foil
4
Bad
Excellent
*
~
250
50
170
2.5
1
9-16
0
Yes
Fair
Complicated
Complicated
Simple
20
Incon.
Bad
*
~
No
5
Exclusively
6
40
|
-
-
-
4
-
-
-
-
4
1
4
*
~
2
4
3
2
1
3
0
4
3
2
2
3
2
1
1
*
~
4
2
4
4
4
66
|
-
Absorber
Global
0.6x0.6x0.2
0.1
2
-
Mirror
8
Excellent
Excellent
*
~
100
40
90
4
4
11-15
1
No
O
None
No
-
None
-
Bad
*
~
A little
5
Exclusively
44
2.3
|
-
-
-
4
-
-
-
-
3
4
4
*
~
0
3
0
3
4
1
2
0
0
0
0
2
2
4
1
*
~
3
2
4
2
0
54
|
-
Abs.+refl.
Direct
0.6x0.6x0.1
0.4
-
-
Mirror
20
Excellent
Good
*
~
160
50
140
4
4
10-16
1-5
No
No
None
No
Simple
30
None
Bad
*
~
A little
5
Exclusively
25
5.6
|
-
-
-
4
-
-
-
-
3
4
3
*
~
1
4
2
3
4
2
3
0
0
0
0
3
3
4
1
*
~
3
2
4
3
3
62
|
-
Abs. + refl.
Direct
0.8x0.8x1.2
0.5
-
8
Mirrors
31
Good
Good
*
~
170
45
250
3
2
10-16
2
Difficult
Difficult
None
No
Simple
30
None
Bad
*
~
Rather
5
Exclusively
44
3.9
|
-
-
-
4
-
-
-
-
2
3
3
*
~
1
3
4
2
2
2
4
-
0
0
0
3
3
4
1
*
~
1
2
4
2
1
61
|
Source. GATE (1979)
Note. The cookers
delivering 370, 470, and 570 W of output are getting the same marks, while only
the four mirror model is shown to develop 250oC. This may be due to the fact
that in Sobaco and Chinese types the cooking vessels were exposed to wind; better
results could be obtained it they are enclosed as suggested.
TABLE 2. ( II Part ) Evaluation of
solar cookers according to characteristics
Name of the
cookers
|
Steam cooker
|
Indoor steam
|
Sobaco
|
Chinese
|
||||
Code used in this
review
|
IDT1
|
IDT4
|
PC 3
|
PRA 2
|
||||
Construction
Principle
Radiation
Dimension
Aperture (m3)
Focal length
Intensification
factor
Reflector material
Weight (kg)
Stability
Portaility
*****
Efficiency
Effective power (w)
Degree of
efficiency
Max. temperature (oC)
Cooking cap. (Kg)
Number of pots
Cooking hrs. (Hrs)
Keeping warm (hrs)
Roasting?
Baking?
Access to food ?
Stirring?
Repositioning?
How often?
Stray light
General handling
*****
Production
Complicated?
Duration (years)
Local materials
Costs (US $)
Power costs (w/US%)
Total
|
-
Reflector
Global
1.5x1x1.4
0.8
-
-
Cr-Ni-steel
60
Good
Very bad
*
~
150
21
100
4
2
9-17
1
No
No
Complicated
Complicated
Very simple
120
None
Good
*
~
Rather
7
Exclusively
62
2.4
|
-
-
-
2
-
-
-
-
0
3
0
*
~
1
1
1
3
2
4
2
-
0
1
1
4
4
4
3
*
~
1
2
4
1
0
48
|
-
Reflector
Global
3x1.5x1.5
3.6
-
-
Pol. Alu
-
Fixed
Excellent
*
~
470
14
100
6
2
10-16
1
No
No
Yes
Yes
-
-
None
Excellent
*
~
Rather
10
Exclusively
150
3.1
|
-
-
-
2
-
-
-
-
2
4
0
*
~
4
0
1
4
2
2
2
-
0
4
4
2
4
4
4
*
~
1
4
4
0
1
57
|
-
Reflector
Direct
2.5x1.8x2
1.7
-
-
-
70
Good
Very bad
*
~
370
28
180
5
2, special
8-16
0.5
Yes
Yes
Complicated
Difficult
Simple
10
Slight
Bad
*
~
Yes
10
Mostly
300
1.2
|
-
-
-
0
2
-
-
-
0
3
0
*
~
4
1
4
4
1
4
1
4
4
1
0
3
0
3
1
*
~
0
4
3
0
0
48
|
-
Reflector
Direct
1.8x1.6x1
-
-
-
-
100
Excellent
Very bad
*
~
560
36
180
5
2
9-17
0
Yes
No
Yes
Yes
Complicated
15
Incon.
Good
*
~
Rather
10
Exclusively
70
8
|
-
-
-
3
-
-
-
-
0
4
0
*
~
4
2
4
4
2
4
0
4
0
4
4
1
1
1
3
*
~
1
4
4
0
3
60
|
Source. GATE (1979)
Note. The cookers
delivering 370, 470, and 570 W of output are getting the same marks, while only
the four mirror model is shown to develop 250oC. This may be due to the fact
that in Sobaco and Chinese types the cooking vessels were exposed to wind; better
results could be obtained it they are enclosed as suggested.
Source:- TIDE., March 1998, 8-1, pp 1-37,
For Comments,
suggestions, contributions contact
Please add,Solar or Solar Cooker, in the subject Solar or Solar
Cooker to avoid your mail being erased as scam
Table 3.
Evaluation of solar cookers according to regional
requirements
Name
|
Code Used here in this
review
|
INDIA
|
China
|
Kenya
|
Sahel
|
Average
|
Sum
From Table
2
|
Von oppen
Box type B
Garg type
Telkes type
Stam cooker
Steam cooker
Sobaco
Chinese
Vita Fresnel
|
FRD
1
BWM
1a
BSM
1d
BFF
1
IDT
3
IDT
4
PC
3
PRA
2
F1
|
261
204
231
239
179
226
200
237
191
|
234
175
207
223
179
236
239
268
165
|
250
204
250
209
212
291
195
264
165
|
258
149
195
201
174
260
235
315
172
|
251
183
121
218
186
253
217
271
176
|
66
54
62
61
48
57
48
60
--
|
Source. GATE (1979)
|
|||||||
- to
reduce the wind effect the cooking vessel should be
placed inside the reflector, and
- the
cooker should be able to fulfill the cooking
requirements of a family of seven.
There are many more
reviews and surveys such as that of the UN, Olwi et al.
(1994), Habeebullah, Khalifa,
Olwi (1995), Khalifa, Taha, Akyurt (1985), and Wentzel (1966). The list is
rather extensive and an attempt is made to cover the most important, if not,
all of them, in this review. Recently from Brigham Young University, USA, Prof.
Stevens has conducted test along with his colleague McMillen on specially
Funnel type of Cookers. The details are available on SCI. They have tested
Solar Funnel Cookers and have suggested some improvements such as using Wire
Baskets etc.
Dr Phillips Fairers
et. al of Florida Solar Energy Center, (FSEC) have excellent testing
facilities, and they have tested mostly COOKIT type of Panel Cookers. They
state that High Back Funnel Cooker perform well.
Apart from taking
several parameters into consideration it is essential to get the opinion of the
housewives if the solar cookers are to become popular.In this regard Mr
Ravindra Pardesi of India, an inventor, is working with his wife Parvati, and
have designed at least two new types of Cookers. A 12 sided double reflector
type and Double funnel type. Both of these are referred to under solar 7 of
this site.
Recently Paul A Funk
of USA along with other scientists has laid out a detailed procedure for
testing Solar Cookers. This was corollary to the 3rd International conference
on Solar Cookers held at Avinashlingam University of Home Science at Coimbatur
of India. The paper has been reproduced in SCIs Solar Cooker Review. But I wish
that Professor and his team had tested a couple of cookers and reported the
results.
Some
recommendations
It was the desire of
the author to build and test all the important models, especially the newer
ones so as to select at least three or four good designs. When the choice is
available, the selection process becomes easy. As regards the box-type cookers,
the general contention is that if they are manufactured on a large scale they
would be cheaper, but then that would mean manufacturing several other related
components such as steel sheets, etc. and although it could generate several
jobs, cost of cookers may not be reduced, and subsidies would not support them
for long. The author strongly recommends do-it-yourself designs for villagers.
Before that, there is
a need to standardize the materials. One can not suggest ordinary Aluminium
foil or aluminized polyester sheets for reflectors. They lose their shine very
soon. It is felt that the most likely candidate for reflectors is polished
stainless steel, but user data for this is not available. For example, how long
will the shine last? When the shape is lost, then can the sheet be polished
locally ? If yes, then can it be done by the housewife or at least by a
traditional knife sharpener with his slightly modified leg operated grinder ?
It is of common
knowledge that even good glass mirrors do not last long in open sunshine
(Buckwalter, McVay 1980; Howe 1981). In fact, there exists a long list of
materials which need testing under the sun, that is sun worthiness. Which glass
mirror is to be recommended ?
As regards glazing,
the author had recommended ‘UV stablized’ transparent polyester materials. But
they did not last for more than three months (Kundapur 1980). One cannot insist
on tempered glass for the box-type cookers as it is very costly, low iron glass
is not easily available, and 4 mm glass would be costly too. Which is the best
alternative ? What if one uses ordinary 3 mm glass? What will be the difference
in performance between ordinary and iron-free glass ? Data is not available
easily. A small difference will not matter, and the author has used only 3 mm
glass, and got satisfactory results.
Similarly, glass wool
or mineral wool insulation cannot be recommended for the villagers, the
material is hazardous. One has to standardize and suggest composites made from
agricultural wastes like rice husk or straw or any other locally available
material. Insulating materials like foam glass is a good alternative (with a k
of 0.036 and a weight of 137 kg/m3, it is as good alternative (with a k of
0.036 and a weight of 137 kg/m3, it is as good as mineral wool) and for urban
cookers too one can definitely recommend the same. This could make the cookers
cost less. Further, the problem of broken glass could also be solved to a
certain extent as broken glass could be used in the manufacture of foam glass.
Absorptive coating
calls for special attention. Is there anything better, safer, and cheaper than
common blackboard paint ? What about the special absorptive stickers,
especially for the cooking vessels, or certain special treatments to darken the
surface ? This is the area which requires serious attention and research. Only
when the scientists have definite answers for aspects like insulation,
absorptive coating, etc. can they think of a massive popularization, program.
This, by itself, will boost the use of solar cookers.
Conclusions
Solar cookers are here
to stay, or to put it in the other way, if we have to preserve our planet then
each and every one of us has to use one or the other type of solar gadget, be
it a cooker a solar water heater or solar photovoltaic panel.
Dr Paul A
Funk et.al.,
have formulated another set of parameters for testing solar cookers the details
could be found if you click
here