GB2264790A

GB2264790A - Refelector dish for solar cooker

Info

Publication number: GB2264790A
Application number: GB9204931A
Authority: GB
Inventors: Rupert Ellis Carr; Dominic Michaelis
Original assignee: ECOVISION Ltd
Current assignee: ECOVISION Ltd
Priority date: 1992-03-06
Filing date: 1992-03-06
Publication date: 1993-09-08
Anticipated expiration: 2012-03-06
Also published as: GB2264790B; GB9204931D0

Abstract

A solar cooker comprises a part-spherical or other concentrating dish comprising flat triangular elements 11 which can be folded substantially flat when not in use. A plurality of the elements may, as shown, form a larger triangle, of which several are assembled to make the dish. An article to be heated is suspended or supported at a focus of the dish and is moved as the sun moves; alternatively the dish may be movably mounted. <IMAGE>

Description

Solar Cooker This invention relates to a solar cooker and solar collector.

Solar cookers have been designed and built over many years and incorporate different methods of harnessing solar energy for the purpose of cooking, generally in the form of hot boxes with reflectors to increase solar intensity, or of parabolic dishes focussing on a target.

Spherical reflectors have been proposed for cooking, and present the advantage that the reflector can be fixed, whilst only the focus moves. However, large spherical shape mirrors are expensive to make, and difficult to transport.

According to the present invention, there is provided a solar cooker formed of a spherical or other concentrating reflector dish made up of folding flat substantially triangular or lozenge-shaped elements, such that it can be packed compactly and easily transported. To achieve optimal heating the food (or other element to be heated) and/or the reflector is moved slowly to track or follow the sun.

In a preferred embodiment there is provided a spherical geometry reflector which concentrates the rays of the sun onto a short linear focus, and if food is located at this focus, it will be heated and cooked. The reflector dish is made up of triangular flat panels with interstices such that, when assembled along geodesic lines, they form spherical sections, or instance, triangular icocahedron sections, five of which in turn form a convex spherical dish. It thus initially can be packed flat into a small volume, which is essential to its transportation to and use in remote areas.The smaller triangular elements can be taped together, or be assembled with a jointing system that allows them to be dismantled if this is necessary, whilst the five larger triangular sections can either be taped, or be assembled for example with edges having touch and close hooked fasteners, or a mechanical joint, and so be demountable.

The food to be cooked, or element to be heated, is suspended at the focus from a structure spanning over the reflector, or is pivoted from the centre of the spher.ical reflector located at the top of a tripod support. Alternatively, the food or other element to be heated can be placed on the ground, and the reflector, provided with an aperture at its crown, can be lifted to fit over the vessel, and then aimed at the sun.

Preferred embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, of which: Figure 1 shows a plan view of the spherical reflector; Figure 2 shows one of five icosahedron triangles that go to make up the reflector, the triangle being shown in its flat format, convenient for folding and packing, before all edges are brought together to generate the spherical geodesic geometry; Figure 3 shows a reflector with a base support structure with the food to be cooked suspended at its focus; Figure 4 shows a reflector with its back against prepared ground and with a tripod collector, the heating vessel being pivoted from the collectors geometric centre to follow the rays of the sun, and the reflector bedded in made-up ground;; Figure 5 shows a geodesic spherical collector mounted on a central support pole guyed back to the surrounding ground, with support poles to relieve any stresses to the reflector, this being a travelling solar heating kit; and Figure 6 illustrates the cooking vessel located on made up ground with the reflector brought in over it so that the focus aligns with the vessel, in this application, the reflector needing to be moved to track the sun.

Referring to the drawings, the cooker is made of a reflective dish, 10, generally circular in plan, as shown in Figure 1, made up from a number of flat triangular elements 11. These are arranged in such a way that they form a generally spherical surface when they are assembled.

Figure 2 shows one set of basic triangular elements 11, arranged on a flat surface, with slits 12, between different elements. When the edges of the elements are brought together, a generally spherical larger triangular panel is generated, for instance, eleven of which would form a total sphere. Five elements shown in Figure 2 are shown assembled in Figure 1, to form a convex spherical geometry dish.

The flat triangular basic elements and their assembly into flat components as shown in Fig 2, allow the spherical dish to be packed compactly for ease of transport and delivery.

The material to be used is reflective, on the concave side, so that incoming solar radiation is reflected by the many triangular basic elements. It can be a reflective metal, or a composite with a reflective coating. The joints between the basic elements can either be taped, or fitted with touch and close hooked fastener pads or a mechanical jointing system.

A very cheap solar cooker can be made from packaging material, such as extruded sandwich plastic panels with a laminated reflective surface for the reflector. The same basic material can be used to form a base structure 26, that gives rigidity to the dish.

Spherical geometry is such that all radiation falling on the dish is reflected towards a single linear focus 13, which is located along the outer half radius of the sphere, in line with the direction of incoming radiation 14, passing through the centre of the sphere 15.

It follows that an element 16, located to intercept radiation at that focus will be heated. For example, a vessel 16, can be suspended over the focus, from trestles 17 on either side, as shown in Figure 3. In the example shown in Figure 1, the radiation falling on the dish is concentrated onto the focus by 180 reflective triangular elements 10. High temperatures can be reached at the focus, where food can be cooked, and water boiled.

A structure 17, can be fixed over the spherical dish, to support a pivot point at its centre 15. A pivot arm 18, pivoting about the sphere's centre 15, and lining up with incoming radiation 14, will ensure that most incoming energy to the dish 10, will be concentrated onto the vessel located at the half radius, in line with the pivot arm. The pivot arm 18, needs to track the sun, whilst the dish 10, remains stationary.

The shadow of the sun cast by the centre point 15, shows the line along which the focus is located, and creates the target to be followed.

The spherical reflector 10, is stationary, and can be built into the ground 20, as illustrated in Fig.4.

In another embodiment shown in Fig.5, the reflector is supported at its base, and fitted with a central pole 20, from the top of which tie rods 21, go to its edges, and from there to guy ropes 22, which anchor it down, over support struts 23, which relieve it of excessive stress. This embodiment recalls the structure of an umbrella, and a flexible, folding material could be used as the reflector in this instance to make up a folding and transportable cooker.

Since the reflector 10, can be of lightweight construction, and is relatively easy to move, whilst the food to be cooked is sometimes heavier, a variation is proposed in Fig.6. in which the food to be cooked 24, is supported on the ground, whilst the reflector 10, is provided with an opening at its base 25, so that it can be brought over the food, aligned with the sun, and then guyed down over support struts. In this embodiment, it is necessary to move the reflector, whilst the food remains stationary.

In this embodiment also, parabolic geometry may be generated to give higher solar concentration ratios, using the same type of general construction.

A preferred reflector has a diameter of 2 meters; such a reflector can generate 2kw of heat at its focus. It is particularly advantageous to use it in developing countries, where it could often replace wood or charcoal fires.

Claims

1. A concentrating reflector dish comprising substantially triangular or lozenge-shaped elements, which are foldable into a flat configuration.

2. A dish according to claim 1 which in its unfolded configuration defines a partial sphere.

3. A dish according to claim 2 wherein the dish defines substantially one eleventh of a total sphere.

4. A dish according to any preceding claim, wherein the elements are arranged in rows to form larger threesided sections.

5. A dish according to claim 4 comprising five of said larger sections.

6. A dish according to any preceding claim comprising means for supporting or suspending an article to be heated at the focus of the dish.

7. A dish according to any preceding claim for heating a stationary article wherein the dish is movably mounted.

8. A concentrating reflector dish substantially as herein described with reference to Figs 1 and 2 and any one of Figs 3 to 6.

9. A method of heating an article using solar radiation and a dish according to any one of claims 1 to 5 wherein the dish is maintained stationary and the article to be heated is arranged to be movable as the sun moves in the sky.

10. A method of heating a stationary article using solar radiation and using a dish according to any one of claims 1 to 5 wherein the dish is arranged to be movable as the sun moves in the sky.

11. A method of heating an article by means of solar radiation substantially as herein described.