I spent some time improving on that concept using a stationary receiver:

http://pics.ww.com/v/jacques/renewables/concentrator/

One of the most fun projects I did back in those days.

I still have the Stirling engine :) (a tiny one, store bought)

I thought that having the Stirling engines on a mobile parabolic mount was a design weakness and figured out a way to do it better.

I was going to say "But wait! They have an experimental plant in Southern California!" I guess I haven't followed things too closely, looks like the whole plan fell apart in late 2009[1].

[1]http://www.solarfeeds.com/greentech-media/15471-so-cal-ediso...