D.I.Y. Solar Cookers

by Dave Pruce

Solar power can be used effectively for cooking on a small scale, if it can be concentrated enough. There are two ways of concentrating the sun’s rays into a point sufficient to raise the temperature of that point to that required for cooking. One is to use a Lens (as in a magnifying glass), but this would be prohibitively expensive. The other is to use a curved mirror to reflect the rays to a central point (the focus). The technical term for the curvature required is a Parabola, meaning that rays hitting the curved surface at (almost) any angle will be reflected to the same point (the focus).

Now this would normally be deemed to be difficult to create as it requires pretty accurate construction, but, a satellite dish (for the same reasons) is a perfect parabola. (See drawing below). The nature of the parabola is such that the dish would not have to move to follow the sun, rather it always reflects the light waves from whatever angle received to hit the same focus point. So, all that remains is to ‘obtain’ a satellite dish of any age (and the bigger the better) and line it with cooking foil to produce a mirror. If the LNB is no longer attached to the dish (it is at the focus) the focus can be found easily by projecting a number (3-4) of perpendicular (900) arms to the dish, and the point at which they intersect is the Focus.

The final part of the job is to channel the point of light/heat to the cooking area. This can be achieved by the judicious use of mirrors (a slightly concave mirror at this point would concentrate the light even more), fibre optics, or a combination of both. A (type of) fibre optic wave guide (that's its technical name) could be produced with a piece of solid cylindrical (1-2 cm would be ideal) glass or plastic bent to shape and again covered with cooking foil (the foil ensures that no light is lost during its travels along the guide).

A final word of warning. Be careful while this is under construction. Once the dish is covered in foil, the focus point will always be hot and VERY bright, even on a relatively dull day, so make sure that you NEVER look at the dish from around the focus, and when the dish is not in use, cover it!

Another favourite is the CooKit, its cheap and easy to make from aluminium foil glued on to a cardboard backing.

Click Here for the full plans.

Good cooking!
Dave.

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