|
A
D.I.Y.
Solar Cooker
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!
Good
cooking!
Dave.
|
