LIGHT CONCENTRATED FROM BELOW
Spherical Mirrors/Parabolic mirror/Rigid Parabola/Shallow Parabola/
Deep Parabola/Asymmetrical Parabola
Concentrator Type
Being a pioneering design, this type of cooker has seen maximum variations, Besides, the design offers several advantages. One of the most important is that the mode of cooking is very much identical to day to day cooking. There are two major types of concentrator solar cookers: (I) cookers which concentrate the light from below, and (ii) cookers which concentrate the light from above.
Heat coming from below is most convenient for routine cooking, hence, many designers have concentrated on this type of cookers. There are a lot of designs in this category, and they are classified on the basis of the type of reflectors used (I) Spherical reflector (S), (ii) Parabolic reflectors (P), (iii) Fresnel types (F), (iv) Cylindro parabolic (CP), and (v) Mirrors plane (MP).
Spherical Mirrors
Spherical mirrors are the simplest type of reflectors, very easy to build and use. Focusssing sun rays are also easy, and if one opts for a moving vessel to meet the focus, cooking can also be done very easily. Such a design was suggested for the first time in the year 1961 by Stam (1961) (Type S1, Figure 1). He suggested a large reflector of 4.0 m diameter made of local material which could even include mud, and the reflector surface suitably smoothed with fine mud/cement and coated with aluminized polyester. An appropriate technology handbook describes a simple method of construction of the spherical mirror in the ground (a tall tripod with a long string to which a stone is attached at the tip, will act as a guide for excavating a hollow in the ground) and after finishing and stabilizing the interior, the reflector material could be stuck to make it into a spherical mirror. Such a mirror, of about 2.0 m in diameter, would do useful work for at least five to six hrs a day.
The cooking vessel could be hung from the tripod or a suitable stand and positioned to cooking vessel could be hung from the tripod or a suitable stand and positioned to meet the focus (Type S 1a). Dr. Halacy 91974) suggests a similar design (Type S 1b, Figure 2). He uses two full and several half cardboard ribs to fabricate the base with a mylar film as a reflector. This device was meant mainly for campers. Bamboo and/or other locally available materials could be used to fabricate such hemispherical baskets (Type S1).
Friday, December 14, 2007
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