On Sat, Sep 24, 2005 at 06:23:35PM +0300, Peter wrote:
> Dr. BAJ said:
> > >I (Peter) said:
> > >
> > >The problem with the parabolic shape proposed is, you cannot make an 
> > >array from them (the focal point is way too close). So it turns out 
> > >that just taking plain glass mirrors (at $6 / sq. meter if what I 
> > >read was true) and warping them slightly in a frame (they will warp 
> > >anyway) will yield something closer to the 10 meter focal distance 
> > >needed for an array.
> >
> > Why 10m?! I actually wanted a much closer focal point. That simplifies 
> > tracking everything. Coordinating a mirror array and then a target 
> > that's 30 ft away is a daunting task. An ideal focal box would be 2-3m 
> > from the center of the array.
> 
> If you use the fixed mirror on a pole and target below it scheme then 
> you need that kind of focal distance.

There's no need to warp individual mirrors; in fact, in some ways it's
counterproductive.

As long as the heat-collecting area on the engine is about the same size
as any individual mirror, just have the flat mirror reflect its particular
patch of sunlight onto the collector without focusing it. The light
intensity at the collector will still be multiplied by the number of
mirrors.

If the mirror itself has a particular focus, then the axis alignment
between the mirror and the collector must be maintained as the mirror
tracks the sun. With a flat mirror, this becomes a don't-care, and each
mirror can be independently steered by a simple heliostat.

-- Dave Tweed
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