The adair wind farm was commissioned in 2008 by midamerican energy. the wind farm, located in iowa on the border of adair county and cass county, is composed of 76 siemens wind turbines each with a rated capacity of 2.3 mw. each wind turbine has a rotor diameter of 93 meters, a coefficient of performance equal to 75% of betz? law, and a combined gearbox and generator efficiency of 96%. it is estimated that the wind farm generates 437 gwh of electricity each year. each wind turbines requires 400 hours of maintenance each year. a. what is the overall efficiency of the wind turbines (%)? b. what is the capacity factor of the wind farm (%)? c. what is the rated wind speed for the wind turbines (m/s)? d. what is the availability of the wind turbines (%)?