REP Wind Power Technologies 4 — Questions and Answers
Question 1: What is the 'cut-in wind speed' of a wind turbine?
- The speed at which the turbine reaches rated power output
- The minimum wind speed at which the turbine begins generating electricity (Correct answer)
- The wind speed that triggers emergency shutdown
- The optimal speed for maximum aerodynamic efficiency
Correct answer: The minimum wind speed at which the turbine begins generating electricity
Cut-in wind speed (typically 3–4 m/s) is the minimum wind speed at which a turbine's rotor produces enough torque to generate net positive electrical output.
Question 2: Which atmospheric layer is most relevant to wind turbine operation and resource assessment?
- Troposphere
- Stratosphere
- Atmospheric boundary layer (Correct answer)
- Mesosphere
Correct answer: Atmospheric boundary layer
The atmospheric boundary layer (lowest ~1–2 km of the atmosphere) is where wind turbines operate and where surface friction, thermal gradients, and turbulence most affect wind resources.
Question 3: What does a turbine's 'power curve' depict?
- Electrical output versus time of day
- Power output as a function of wind speed (Correct answer)
- Voltage and current at the point of interconnection
- Generator torque versus rotational speed
Correct answer: Power output as a function of wind speed
A turbine's power curve is a graph showing electrical power output (kW or MW) at each wind speed from cut-in through rated to cut-out conditions.
Question 4: Why are wind turbine blades twisted along their length?
- To reduce ice accumulation on the leading edge
- To account for varying relative wind angles from root to tip due to rotational speed (Correct answer)
- To increase structural stiffness against flapwise bending
- To improve visual aesthetics and reduce radar cross-section
Correct answer: To account for varying relative wind angles from root to tip due to rotational speed
Blade twist compensates for the fact that tip sections move much faster than root sections, ensuring each blade section encounters wind at an optimal angle of attack.
Question 5: What is 'curtailment' in the context of wind power generation?
- Scheduled maintenance downtime for turbines
- Deliberate reduction of turbine output below available capacity (Correct answer)
- Emergency shutdown triggered by extreme weather
- Reduction in government subsidies for wind projects
Correct answer: Deliberate reduction of turbine output below available capacity
Curtailment is the intentional reduction of a wind farm's output, typically ordered by grid operators when generation exceeds transmission capacity or grid demand.
Question 6: Which material is predominantly used in modern large-scale wind turbine blades?
- Aluminum alloy
- Carbon steel
- Glass fiber reinforced polymer (GFRP) (Correct answer)
- High-density polyethylene
Correct answer: Glass fiber reinforced polymer (GFRP)
Glass fiber reinforced polymer (fiberglass) composites are the dominant blade material due to their high strength-to-weight ratio, fatigue resistance, and cost-effectiveness.
Question 7: What is the significance of a wind turbine's hub height in energy production?
- Higher hub heights reduce electrical transmission losses
- Greater hub height accesses higher, more consistent wind speeds due to wind shear (Correct answer)
- Hub height determines the number of blades the rotor can support
- Taller towers reduce noise impact at ground level only
Correct answer: Greater hub height accesses higher, more consistent wind speeds due to wind shear
Wind speed generally increases with height due to wind shear (reduced surface friction), so taller towers capture faster, more consistent winds and produce more energy.
REP Wind Power Technologies 4
What is the 'cut-in wind speed' of a wind turbine?