From: root@mauve.demon.co.uk   
      
   Henry Spencer  wrote:   
   > In article ,   
   > ANTIcarrot  wrote:   
   >>How much energy can mirros focus onto a solar panel before it begins to   
   >>melt?   
   >   
   > A more fundamental problem than melting is that solar-cell efficiency   
   > drops off as the cells get hot, although this is less important for   
   > advanced cell materials than it was for silicon.   
      
   Standard solar cells are some 0.3mm thick.   
   To create a 1C temperature differential over this (silicon has a thermal   
   conductivity of 150W/K/m) will take some 500KW/m^2.   
   I think that it will take around 20C to get significant strains in the   
   solar cell between the front and the back, so a figure of some 10MW/m^2   
   might not be unreasonable.   
      
   However...   
   Silicon cells are not just silicon, but require a network of metallisation   
   over it to carry the current.   
      
   But this isn't the primary problem.   
   The primary problem is what do you do with the heat?   
   If you paint the back of the solar cells black (in IR) then point them   
   at the sun, in deep space, they will heat to around 0C (plus or minus   
   20C).   
   But, if you concentrate the sunlight to say 4 times, then the temperature   
   rises to some 100C, at 10 times some 324C.   
      
   At some point, you'r cells are going to, if not melt, degrade efficiancy   
   significantly.   
      
   To avoid this, you have to actively cool the cells.   
   But then you run into the problem that the area you need for the thermal   
   radiators is pretty closely the area of the solar cells, unless you   
   use active heat-pumps.   
      
   You may be able to do quite a little bit better if you filter the light   
   at the mirror, and reduce the IR/blue, as these heat the cell without   
   producing (proportionally) as much electricity.   
      
   But then, it's likely that the filter will not quite be free in some   
   way.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)