Introduction

In this investigative lab, students will construct a functional anemometer to measure wind speed, and use their data to calculate the wind energy potential of a wind turbine. They will simulate how engineers determine optimal turbine locations by applying scientific and engineering practices.

Investigation Outline

Materials

Student Objectives

Students will be able to

• Construct and calibrate a basic anemometer to accurately measure wind speed.
• Collect wind speed data under various conditions and analyze it using the wind power equation to evaluate energy potential.
• Explore how variations in wind speed and turbine dimensions influence energy output, and apply findings to inform wind turbine placement decisions.

Part 1: Analyzing the Wind Power Formula

• Provide students with the Student Handout. They will use this resource as a guide through the investigation. 
• Begin the class by leading a guided discussion on the different factors that influence the amount of energy produced by wind turbines. Encourage students to think about environmental conditions (such as wind speed and air density), turbine design (like blade length and efficiency), and location (elevation, proximity to obstacles, etc.).
• To introduce students to real-world examples of successful wind energy farms around the world, show students the Switch Chapter 11 Electricity Options: Wind video.
• Introduce students to the Wind Power formula: Power (W) = 0.5 x ρ x A x v³
• Discuss the equation and what each variable means. Students will have the following table on their handout, defining the variables in the wind power equation.

Part 2: Building an Anemometer and Calibration

• If students will be building their own anemometers, provide them with the required materials. They will need to carefully follow the instructions on the student handout.
• Students will follow instructions on the student handout to use the anemometer to collect wind data, calculating revolutions per minute for three different fan settings.
• Students will conduct three trials for each fan setting, and find the average revolutions per minute. If needed, guide your students through this calculation with the following steps.

Wind Speed Calculation Guide
Students will use the average revolutions per minute from their anemometer data.
A. Calculate distance per minute (cm/min) = Revolutions per minute (anemometer data) x distance per revolution
B. Calculate distance in meters per minute (m/s) = (cm/min) x  (1 m/100 cm)
C. Calculate distance in meters per second  (m/s) = (m/min)  x (1 min/60 seconds)

Part 3: Simulated Windmill Calculations

• Now that students have measured various wind speeds, they will put themselves in the role of energy engineers, deciding whether to install a wind turbine at a specific site. 
• First, students will choose one local location (in the same region or state) where they think a wind turbine might ideally be located.
• Following instructions on the student handout, students will calculate the swept area (A) of a 40-meter blade turbine and use an Air Density Calculator to measure the air density (km/m³) of their location, after researching the current month’s average air pressure, temperature, humidity and altitude.
  *Alternatively, groups could be assigned a variety of locations to compare which would be best suited for wind power. 
• Students will use the wind power formula to calculate energy output for different input values. They will then compare the results and answer reflection questions to analyze patterns and draw conclusions.

Answer Key: Sample Data & Calculations 

Part 1: Analyzing the Wind Power Formula Answer Key

Answers A-E: Many factors could be identified including: wind speed, temperature, humidity, air density, turbine height, blade length, turbine location, obstacles near turbines, turbine efficiency, etc. 
F. The symbol ρ represents air density.
G. Factors affecting air density include altitude, atmospheric pressure, temperature, and humidity. 
H. If air density increases, then wind power increases. 
I. Given the equation, there is a direct relationship between wind power and air density. 
J. A stands for the area of the circle that the turbine blades move through. 
K. The formula for this area is A = πr²
L. The variable v in the equation represents the wind velocity and should be measured in units of m/s. 
M. Wind velocity is measured using an anemometer. 

Part 2: Calibration and Wind Speed Calculations Sample Data

A. Low Fan Setting Data Table

B. Medium Fan Setting Data Table

C. High Fan Setting Data Table

D. Measure the diameter of your anemometer’s circular path (cm)
Sample data: 17 cm 
E. The distance per revolution (cm) can be found with the following formula: π x diameter (Note: You may use 3.14 for π)
Sample Calculation: Distance per revolution = π (17 cm) = 53.4 cm/revolution

F. Low Fan Setting Calculations Table (Sample Calculation)

G. Medium Fan Setting Calculations Table (Sample Calculation)

H. High Fan Setting Calculations Table (Sample Calculation)

Part 3: Simulated Windmill Sample Calculations

A. Month: July
B. Average Temperature: 85.5 ^oF 
C. Average Humidity: 69% 
D. Average Air Pressure: 29.54 in of Mercury
E. Altitude: 489 feet above sea level 

F. Wind Turbine Survey Data Table (Sample Data)

G. Wind Power Calculations Table (Sample Calculation)

H. 366 W x (0.4) = 146 W 
I. Answers will vary.
J. Even small changes to wind speed will have a significant effect on the overall power output. This will occur because in the wind power equation, the velocity is cubed, thus having a big impact. 
K. The power output drops to zero. This occurs because the wind turbine must be shut down and rotation stopped to prevent damage to the equipment. 
L. At wind speeds of 40 km/hr, the expected output is roughly 0.7-0.8 MW. The best site would be one that has winds consistently at, or near, the rated speed to ensure maximum performance. 
M. The graph shows an exponential increase up to the rated speed, demonstrating that slower than optimal wind speeds have a much lower output. It also shows that very high wind speeds also result in no power being produced. 
N. Answers will vary but may include: acceptance of local stakeholders (due to sight, noise, etc of turbines), migratory patterns of birds, distance from the grid and other transmission lines, accessibility for maintenance, zoning laws, cost of installation and maintenance, weather extremes in the area, etc. 
O. Answers will vary but students may have inconsistencies in counting the number of revolutions of the rotating anemometer as it can be particularly difficult to count at higher wind speeds. This would certainly affect the accuracy of the results.
Note: To compare, students could apply the wind power equation using some theoretical wind speeds (e.g. 20 – 40 miles/hour or 9-18 m/s) to obtain more accurate values.