Modern wind-driven electricity generators began appearing during the late 1970s. At that time, the average power output of a wind turbine unit was about 50 kW with a blade length of 8 m. Since then,the size of the machines has increased dramatically. Nowadays,
the typical values for power output of the modern turbines
deployed around the world are about 1.5 to 3.5 MW with blade
lengths of more than 40 m for onshore and 60 m for offshore
applications. Simultaneously, the cost per kilowatt has
decreased significantly, and the efficiency, reliability, and
availability of the machines have definitely improved.