Thanks everyone who came by for my show and tell. It was fun (my voice should be back tomorrow!)
Do hit me up if you had questions or suggestions of who to talk to to help me roll this project forward... More as I know it.
And a white paper (oldie but goodie) at www.solarspork.com
Since it was written, I have found some important loss mechanisms and buttoned them up. I have not had the funds to reanalyze the optic gains and "cash in" those improvements in a new analysis. The main new gain is from the enormous drop in the absorber(emitter) area. It is around .03 of the original area and the reemission is further suppressed by being aimed down into the mirror array rather than out to the cool sky directly. So together they should get our net efficiency of collection at 150C up. But the radiative exchanges are not the sort of things I intuit well - and why intuit when some physics (by smarter people) can do the trick.
The hunt for a suitable cell has hit a jackpot (but I am without funds to buy a small set) in three forms
Alta Devices: Gallium Arsenide thin film cells (I have to de-concentrate for now to use them) I have them in hand.
A small set of silicon concentrators rated for 70 suns (again de-concentrate to use them in prototyping/proof of concept work) that I got from a surplus.
An expensive in small quantities but right on the spec set of silicon "vertical Junction" cells of any size I need/want. I just have to give up $2000 for a minimum order (ugh.)
All of this is compromised by the un-patentability of the device: no monopoly on offer means the returns are compromised for me. I'll work it out, stay tuned!