NABCEP NABCEP Wind Energy Site Assessment 2 — Questions and Answers
Question 1: What is 'shadow flicker' in the context of wind turbine installations?
- The turbine's internal control panel light indicator
- The alternating light and shadow caused by rotating turbine blades passing in front of the sun, affecting nearby residences (Correct answer)
- The visual effect of ice on turbine blades
- The light reflection from turbine nacelle coatings
Correct answer: The alternating light and shadow caused by rotating turbine blades passing in front of the sun, affecting nearby residences
Shadow flicker occurs when rotating turbine blades periodically interrupt sunlight reaching nearby windows, creating a strobe-like effect that can be disturbing to occupants; most jurisdictions limit flicker to 30 hours/year.
Question 2: What wind turbine component converts the kinetic energy of wind into rotational mechanical energy?
- The nacelle
- The rotor (hub and blades) (Correct answer)
- The transformer
- The yaw drive
Correct answer: The rotor (hub and blades)
The rotor — consisting of the hub and blades — captures wind kinetic energy and converts it to shaft rotation, which is then converted to electrical energy by the generator.
Question 3: What does 'capacity factor' mean for a wind turbine installation?
- The turbine's maximum rated power output
- The ratio of actual annual energy produced to the theoretical maximum if the turbine ran at full rated power all year (Correct answer)
- The number of hours per year the turbine operates
- The turbine blade's structural safety factor
Correct answer: The ratio of actual annual energy produced to the theoretical maximum if the turbine ran at full rated power all year
Capacity factor compares actual output to the theoretical maximum, reflecting how well real-world wind conditions utilize the turbine's full capacity; US land-based wind typically achieves 25–45%.
Question 4: What is the significance of the 'cut-in wind speed' of a wind turbine?
- The speed at which the turbine must be shut down for safety
- The minimum wind speed at which the turbine begins generating electricity (Correct answer)
- The turbine's peak efficiency wind speed
- The average wind speed required for turbine installation
Correct answer: The minimum wind speed at which the turbine begins generating electricity
Cut-in wind speed is the minimum wind speed at which the rotor generates enough torque for the generator to produce useful electricity; below this speed the turbine is idle.
Question 5: What type of permit is typically required before installing a small wind turbine in a residential zone?
- Only a utility interconnection agreement
- A zoning or use permit, building permit, and utility interconnection agreement at minimum (Correct answer)
- Only a building permit
- No permit is required for turbines under 10 kW
Correct answer: A zoning or use permit, building permit, and utility interconnection agreement at minimum
Small wind installations typically require multiple permits: a zoning or special use permit for the structure's height and land use, a building permit for the foundation and tower, and a utility interconnection agreement for grid-tied systems.
Question 6: What is 'wake effect' in a multi-turbine wind project and why does it affect siting?
- The heat generated by turbine nacelles warming downwind areas
- The turbulence and reduced wind speed in the downwind shadow of an upstream turbine, reducing energy capture of turbines behind it (Correct answer)
- The visual impact of turbines on the horizon
- The noise created by turbine blades at night
Correct answer: The turbulence and reduced wind speed in the downwind shadow of an upstream turbine, reducing energy capture of turbines behind it
Upstream turbines extract energy from the wind and create a turbulent wake; turbines sited too close downwind operate in this reduced, turbulent flow and produce less energy with higher fatigue loads.
NABCEP NABCEP Wind Energy Site Assessment 2
What is 'shadow flicker' in the context of wind turbine installations?