Aquatic Plants Digest V2 #54

 Use some kind of "light pipe":  Outside the house (or wherever)
  catch the light with a parabolic mirror, and reduce it into
  a glass rod or fiber optic cable (make sure it's big enough to
  handle the light and not burn out).  You can then run this cable
  through the walls or wherever (like an electric cord), and then
  re-expand it with a lens over the tank.  In essence, you run your 
  "light" like you run your electricity or water.

There is a company that manufactures a "skylight" that uses mirrors to
pipe the light wherever you want it. I have been considering doing just
what you are talking about but I have real reservations about sunlight
and algae. If I remember correctly, the cost for the "light pipes" is
about $250 each. If I can find the flyer I had, I'll snail-mail you a
Jphealy at sysconn_com