Selection of best design Continued --

Table 3. Evaluation of solar cookers according to regional requirements

• to reduce the wind effect the cooking vessel should be placed inside the reflector, and
• the cooker should be able to fulfil the cooking requirements of a family of seven.

There are many 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. Apart from several parameters taken into consideration it is essential to get the opinion of the housewives if the solar cookers are to become popular.

Some recommendations

It was the desire of the author to build and test all the important models, especially the newer ones so as to design but at least three or four. 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 woul 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, programme. 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.

Source:- TIDE., March 1998, 8-1, pp 1-37, For Comments, suggestions,contributions contact < ashok_kundapur@yahoo.com>

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