NABCEP Small Wind Installer 1 — Questions and Answers
Question 1: What is the generally recommended minimum average annual wind speed for a cost-effective small wind turbine installation?
- 6 mph (2.7 m/s)
- 10 mph (4.5 m/s) (Correct answer)
- 15 mph (6.7 m/s)
- 20 mph (8.9 m/s)
Correct answer: 10 mph (4.5 m/s)
A minimum average annual wind speed of approximately 10 mph (4.5 m/s) is generally required for a small wind system to be economically viable.
Question 2: Wind power is proportional to the cube of wind speed. If wind speed doubles, how does the available power in the wind change?
- It doubles
- It quadruples
- It increases by a factor of six
- It increases by a factor of eight (Correct answer)
Correct answer: It increases by a factor of eight
Because wind power follows P ∝ V³, doubling the wind speed increases available power by 2³ = 8 times.
Question 3: Which instrument is the primary tool used to measure wind speed during a small wind site assessment?
- Barometer
- Anemometer (Correct answer)
- Hygrometer
- Pyranometer
Correct answer: Anemometer
An anemometer measures wind speed and is the standard instrument used in wind resource assessments to collect site data.
Question 4: Per the widely accepted '30-foot rule,' how much taller should a small wind turbine hub be above any obstruction within 500 feet of the installation?
- 10 feet
- 20 feet
- 30 feet (Correct answer)
- 50 feet
Correct answer: 30 feet
The 30-foot rule states a turbine hub should be at least 30 feet above any obstruction within 500 feet to avoid turbulent wake effects that reduce output and increase fatigue loads.
Question 5: What is the Rayleigh distribution used for in small wind site assessment?
- Calculating tower foundation loads
- Estimating turbine oil change intervals
- Modeling the statistical frequency of wind speeds at a site (Correct answer)
- Determining electrical conductor sizing
Correct answer: Modeling the statistical frequency of wind speeds at a site
The Rayleigh distribution is a statistical model that estimates how often each wind speed occurs at a site, enabling annual energy production estimates.
Question 6: What is a wind shadow (turbulence zone) that forms downwind of an obstruction such as a building or tree line?
- A region of accelerated wind speed behind the obstacle
- A zone of reduced and turbulent airflow extending 10–20 times the height of the obstruction downwind (Correct answer)
- An area where ice accumulates on turbine blades
- A zone where wind changes direction by more than 45 degrees
Correct answer: A zone of reduced and turbulent airflow extending 10–20 times the height of the obstruction downwind
Obstacles create a turbulent wake zone extending 10–20 times their height downwind, which degrades energy output and increases mechanical fatigue on turbines sited within it.
Question 7: Which of the following best describes a 'furling' mechanism on a small horizontal-axis wind turbine?
- A blade pitch system that maximizes power at all wind speeds
- A mechanical disc brake applied during maintenance shutdowns
- A passive system that turns the rotor out of the wind to prevent overspeed in high winds (Correct answer)
- An electronic inverter that converts variable-frequency AC to grid-compatible AC
Correct answer: A passive system that turns the rotor out of the wind to prevent overspeed in high winds
Furling is a passive overspeed protection mechanism in which the tail folds or the rotor yaws sideways, reducing swept area exposure when wind speeds exceed safe operating limits.
