MW of installed capacity
Have a read of David MacKay's excellent Sustainable Energy Without the Hot Air Chapter 4, Wind. On page 33 he explains 


  This conclusion – that the maximum contribution of onshore wind, albeit “huge,” is much less than our consumption – is important, so let’s
  check the key figure, the assumed power per unit area of wind farm
  (2 W/m2), against a real UK wind farm.
  
  The Whitelee wind farm being built near Glasgow in Scotland has 140
  turbines with a combined peak capacity of 322 MW in an area of 55 km2.
  That’s 6 W/m2, peak. The average power produced is smaller because the
  turbines don’t run at peak output all the time. The ratio of the average
  power to the peak power is called the “load factor” or “capacity factor,”
  and it varies from site to site, and with the choice of hardware plopped
  on the site; a typical factor for a good site with modern turbines is 30%.
  If we assume Whitelee has a load factor of 33% then the average power
  production per unit land area is 2 W/m2 – exactly the same as the power
  density we assumed above.


On the following page he answers the question


  Wind turbines are getting bigger all the time. Do bigger wind turbines
  change this chapter’s answer?
  
  Chapter B explains. Bigger wind turbines deliver financial economies
  of scale, but they don’t greatly increase the total power per unit land area,
  because bigger windmills have to be spaced further apart. A wind farm
  that’s twice as tall will deliver roughly 30% more power.