A wind turbine generator is a machine that changes the kinetic energy of moving air into electrical energy. Wind pushes on the blades, causing the rotor to spin, and that rotation is carried into the nacelle at the top of the tower. Inside the nacelle, mechanical parts control speed and transfer torque to a generator.
Understanding this system shows how renewable energy machines use physics to produce useful electric power.
Key Facts
- Wind power available to the rotor is P = 0.5 rho A v^3, where rho is air density, A is swept area, and v is wind speed.
- Swept area is A = pi r^2, so doubling blade length increases the captured wind area by a factor of 4.
- Mechanical power from rotation is P = tau omega, where tau is torque and omega is angular speed.
- Electromagnetic induction follows Faraday's law: emf = -N dPhi/dt.
- A generator produces current when changing magnetic flux through coils creates an induced voltage.
- No turbine can capture all wind energy, and the Betz limit gives a maximum ideal efficiency of 59.3 percent.
Vocabulary
- Nacelle
- The nacelle is the housing at the top of a wind turbine that contains the shaft, gearbox, generator, brake, and control systems.
- Rotor
- The rotor is the spinning assembly made of the blades and hub that captures energy from the wind.
- Torque
- Torque is the twisting effect of a force that causes an object such as a turbine shaft to rotate.
- Electromagnetic induction
- Electromagnetic induction is the production of voltage when magnetic flux through a coil changes.
- Gearbox
- A gearbox is a set of gears that changes rotational speed and torque between the rotor shaft and the generator.
Common Mistakes to Avoid
- Treating wind power as proportional to wind speed is wrong because P = 0.5 rho A v^3, so a small increase in wind speed can greatly increase available power.
- Forgetting to use swept area is wrong because the turbine captures wind over a circular area, not just along the blade length.
- Assuming the generator creates energy is wrong because it converts mechanical energy from the spinning shaft into electrical energy.
- Ignoring efficiency losses is wrong because friction, turbulence, electrical resistance, and generator heating reduce the electrical power delivered.
Practice Questions
- 1 A turbine has blade radius 20 m. What is its swept area? Use A = pi r^2 and pi = 3.14.
- 2 Air density is 1.2 kg/m^3, swept area is 500 m^2, and wind speed is 8 m/s. Calculate the available wind power using P = 0.5 rho A v^3.
- 3 Explain why a wind turbine generator needs changing magnetic flux to produce voltage, and describe one way the spinning rotor helps create that change.