Harvesting the Wind
Wind turbines convert the kinetic energy of moving air into electricity through aerodynamic lift on rotating blades driving a generator. Modern utility-scale turbines have rotor diameters exceeding 150 meters and rated capacities above 10 MW, with offshore models pushing past 15 MW. The physics is elegant: wind power scales with the cube of wind speed and the square of rotor diameter, making larger rotors in windier locations dramatically more productive.
The Betz Limit: Nature's Speed Limit
In 1919, Albert Betz proved that no turbine can extract more than 16/27 (59.3%) of the wind's kinetic energy. The proof is beautifully simple: if a turbine extracted all the energy, the air would stop, blocking incoming wind. If it extracted none, no power is produced. The optimum occurs when the air slows to one-third its upstream velocity. Modern turbines achieve power coefficients of 0.45-0.50, remarkably close to this theoretical limit.
Power Curves and Blade Pitch
A turbine's power curve shows output versus wind speed and has three key regions: below cut-in speed (no power), between cut-in and rated speed (power increases with V^3), and above rated speed (power is held constant by pitching blades). The blade pitch angle controls the aerodynamic angle of attack - optimized for maximum Cp at moderate winds, then rotated toward feather to shed excess energy in high winds.
From Wind Resource to Annual Energy
A turbine's economic value depends on annual energy production (AEP), which integrates the power curve against the site's wind speed probability distribution (typically a Weibull distribution). The capacity factor - actual output divided by rated output over a year - captures this. Offshore sites with steady, strong winds achieve capacity factors of 50%+, making them increasingly competitive with fossil fuels.