Orbital solar power, since its introduction nearly 15 
  years ago, has grown considerably.** Various new stations 
  are now in place, able to provide continuous power to Earth.

http://physics.ucsd.edu/do-the-math/2012/03/space-based-sola...

  On a yearly basis, then, getting continuous 24-hour solar 
  illumination beats the California desert by a factor of 2.6 averaged 
  over the year, ranging from 2.0 in the summer to 3.5 in the winter. 
  One of my points will be that launching into space is a heck of a lot 
  of work and expense to gain a factor of three in exposure. It seems a 
  good bet that it’s cheaper to build three times as many panels and 
  stick them on the ground. It’s not rocket science.

  [...]

  At this level, our 3.6 km diameter collecting area would generate 
  about 40 GWh of energy in a day, at an assumed reception/conversion 
  efficiency of 70%. By comparison, a flat array of 15%-efficient PV 
  panels occupying the same area in the Mojave Desert would generate 
  about a fourth as much energy averaged over the year. So these 
  beaming hotspots are not terribly more concentrated than what the 
  sunlight provides already. Again, I find myself scratching my head 
  as to why we should go to so much trouble.