From: jtkare@attglobal.net   
      
   Henry Spencer  wrote:   
      
   > In article ,   
   > Alex Terrell  wrote:   
   > >How many W/m2 can solar panels produce, assuming concentrated or laser   
   > >light?   
   >   
   > Nobody has done much work on optimizing solar panels for laser illumination,   
   > so I think the answer to that one is "nobody knows".   
   >   
      
   It's not clear what the upper limit would be, but somewhere in the range   
   of 2-3 kW/m^2 should be straightforward.   
      
   There are some additional advantages to using photovoltaics with lasers,   
   vs. sunlight.  In particular, with narrow-band illumination, one can use   
   flat diffractive concentrators in place of curved reflectors, and can   
   put efficient antireflection coatings on the cell surfaces.   
   >   
   > >...Alternatively, could the laser be converted directly into heat to   
   > >drive a closed cycle engine?   
   >   
   > Converting the laser beam into heat is no big deal in priniciple, but then   
   > you run into the inefficiency of heat engines, and the need to get rid of   
   > a lot of waste heat with a radiator system.  Solar arrays are easier.   
      
   There are actually some ingenious schemes for various kinds of resonant   
   laser absorption which allow one to, in principle, get a very high   
   thermodynamic efficiency.  Effectively, one uses the fact that the laser   
   beam itself has an enormous "temperature"  and very low entropy.  (David   
   Brin made somewhat bogus use of this to make a refrigerator that would   
   work efficiently at an ambient temperature of several electron volts   
   (>>10,000K) in _Sundiver_)  I'm not aware of any efforts to make a   
   practical power converter based on these approaches.  OTOH, the high   
   concentrations, and therefore high receiver temperatures, possible with   
   a laser would make possible pretty high efficiencies (>50%) even with a   
   conventional heat engine cycle; it would just be a pain in the a** to   
   develop the hardware.   
      
   Jordin   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)