Selection of the best design

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

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 )

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

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,

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