Bloomberg has an article at the increasing size and efficiency of wind turbines - World's Biggest Windmills Now Make Jumbo Jets Look Tiny.
As they got bigger, the units became more efficient, boosting global installations 23 percent last year to a record 63.5 gigawatts, which at full tilt would be about as much as what flows from 63 nuclear reactors. ... “The doubling of turbine size this decade will allow wind farms in 2020 to use half the number of turbines compared to 2010,” said Tom Harries, an industry analyst at Bloomberg New Energy Finance. “This means fewer foundations, less cabling and simpler installation -- all key in slashing costs for the industry.”
The average turbine installed in Europe was 4.1 megawatts last year, 28 percent larger than in 2010, according to the London-based researcher, which expects 6.8 megawatts to be the norm by 2020. Harries said Siemens has hinted it’s working on a 10 megawatt turbine.