Wow! The concepts underlying Betz's Law are intuitive, though, still too clever for me!

I found the economic implications interesting. Given a Betz Limit of ~59% wind energy extraction, "utility-scale wind turbines" ...

  A) can only capture 80% of the peak (Betz Limit)
  B) achieve 25-60% of their potential output (constant wind) on an annual basis

Combining this with the NREL maps shared by animats below, you can make SWAG's for energy production in locations.