Large wind turbines are the most efficient and they keep on growing. Difficulties with initial installation and then maintenance on offshore units makes their high efficiency even more important.
Currently, there are two large Siemans turbines one with a 465 foot height and 394 foot diameter blade path producing 3.6 megawatts, the other a bit taller at 588 feet and blades coming in at a 505 foot diameter produces 6 megawatts. The big one from Vestas is 728 feet tall with the blade diameter running at 538 feet.
A report from the European Commission says a 20-megawatt turbine with a blade diameter of 788 feet is “feasible”.
Source: Sierra, Jan/Feb 2015