Investigating the Use of a Variable-Pitch Wind Turbine to Optimize Power Output Under Varying Wind Conditions.

1. Galen Maly Yorktown High School Investigating the Use of a Variable-Pitch Wind Turbine to Optimize Power Output Under Varying Wind Conditions.

2. Background • In 2001, 0.15 percent of electricity consumed in the U.S. came from wind turbines. • If 0.6 percent of the land in the U.S. was used for wind farms, then those turbines could produce 15 percent of the electricity.

3. How Wind Turbines Work • Wind turbines change the kinetic energy of the wind into electricity in a 2-step process. • First, the kinetic energy of the wind is turned into rotational energy of the rotor by the blades. • Second, rotational energy of the rotor is turned into electricity by a generator.

4. Lift vs. Drag • The kinetic energy of the wind is harnessed through two forces, lift and drag • Drag, the force of the real wind pushing on the blade gets the rotor spinning. • After the rotor begins spinning, an induced wind occurs. • The induced wind combines with the real wind to form the resulting wind. • When the angle between the resulting wind and the blade is about 15 degrees, lift occurs.

5. Pitch • Pitch is the angle of the wind turbine blade. • Pitch can be measured as an angle or a unit of length (the distance the blade would travel were it to be spun 360 degrees through a solid like a screw) • A fixed-pitch wind turbine is a wind turbine that cannot change the angle of its blades. • A variable-pitch wind turbine has the ability to change the angle of its blades.

6. Purposes and Hypotheses • The overall purpose was to determine if a variable-pitch wind turbine would be more effective than a fixed-pitch turbine in converting the kinetic energy of wind into electrical power. • This overall purpose was divided into five objectives

7. Objective 1 • To validate the previous year’s results by testing the power output from fixed-pitch blades with a more consistent higher-speed wind source (a wind tunnel). • The hypothesis was that as pitch decreased and wind speed increased, output from the wind turbine would increase.

8. Objective 2 • To measure the RPMs of the wind turbine rotor in order to determine the angle of attack of the resulting wind on the blade. • The hypothesis was that the angle of attack would be in the range of 15 degrees.

9. Objective 3 • To determine if electrical output of the wind turbine could be maximized by varying blade pitch. • The hypothesis was that a variable-pitch wind turbine is able to achieve higher levels of output than a fixed-pitch wind turbine.

10. Objective 4 • To see if it is possible to create a computer program to optimize the electrical output of a variable-pitch wind turbine through real-time measurement of RPMs. • The hypothesis was that a program could be written that uses real-time RPM input to achieve optimized pitch for maximum power output.

11. Objective 5 • To create a computer program that adjusts pitch in response to a given wind speed in order to optimize power output. • The hypothesis was that a program could be written to do so.

13. Procedures: Programming Four programs were written in iC for use on a microprocessor attached to the turbine. • Set the pitch at a specific angle at the blade’s midpoint. • Slowly increased the pitch in 1-degree increments. • Read in the RPMs of the wind turbine and kept adjusting the blade pitch for a given wind speed until maximum RPMs were achieved. • Read in wind speed and set the pitch for maximum output using an equation derived from previous experimentation.

14. Procedures: Objective 1 • To test the first hypothesis, voltage and RPM outputs were recorded at pitches of 15, 34, 45, and 60 degrees at several different wind speeds ranging from 4.5 to 14.3 m/s. This process was repeated for two trials, and results were gathered in a data table.

15. Procedures: Objective 2 • The second hypothesis was tested by gathering data on the RPMs at the optimum pitch for several wind speeds. • The RPMs were used to calculate the speed of the blade at its midpoint and, from that, the angle of attack on the blade.

16. Procedures: Objective 3 • The third hypothesis was tested by increasing the pitch of the blade until the rotor would begin spinning. Then, the pitch was decreased towards a pitch of zero (an ability unique to variable-pitch wind turbines). • The power output was recorded at every degree of pitch

17. Procedures: Objective 4 • The fourth hypothesis was tested by using the program to optimize the pitch of the wind turbine at pitches from 4.5 to 14.3 m/s in both the wind tunnel and using a fan. The program was run twice (due to time limitations at the wind tunnel) for each wind speed, and results were collected. • Regression statistical analyses for the data were conducted.

18. Procedures: Objective 5 • The fifth hypothesis was tested by attaching a sensor to a Kestrel wind meter to measure wind speed and feeding that information to the Handyboard.

19. Results/Conclusions: Objective 1 • Higher pitch blades begin to spin first at lower wind speeds, but at high wind speeds, lower pitch blades spin faster and produce higher output than higher pitch blades. • A higher-pitch blade can translate more of the wind’s drag force into rotational motion, so higher-pitch blades are more effective at low wind speeds. • Once the blade starts spinning, the blade’s rotational movement causes a head wind, and lift makes the blade spin faster. Once lift dominates drag, the lower-pitch blades can spin faster and produce more electricity.

20. Results/Conclusions: Objective 1 Effect of Wind Speed on Power Output Using Fixed-Pitch and Programmed Variable-Pitch Blades

21. Results/Conclusions: Objective 2 • By knowing the RPMs of the turbine rotor shaft, the speed of the blade at any distance from the shaft can be computed. • The speed of the real wind and induced wind can then be used to compute the velocity of the resulting wind on the blade. • The angle of attack can then be computed based on the blade’s pitch angle. • The angles of attack at the midpoint were mostly between 10 and 20 degrees, with an average of 14.9 degrees. Hence, the hypothesis was supported.

22. Results/Conclusions: Objective 3 Effect of Varying Blade Pitch on Power Output When Wind Speed is Constant (6.3 m/s)

23. Results/Conclusions: Objective 4 • For every wind speed, the maximum output discovered by the program was close to being equal to or higher than any other output from the wind turbine. • In other words, a variable-pitch turbine can be programmed to constantly seek maximum power output.

24. Results/Conclusions: Objective 4 Effect of Wind Speed on Power Output Using Fixed-Pitch and Programmed Variable-Pitch Blades

25. Results/Conclusions: Objective 4 Effect of Wind Speed on Optimum Pitch

26. Results/Conclusions: Objective 5 • This objective was not achieved because the Handyboard had insufficient processor power to be able to read every RPM of the wind meter as signaled by the sensor. • The sensor could read in very low wind speeds accurately, but was completely unreliable at high wind speeds.

27. Results/Conclusions: Overview • Variable-pitch wind turbines are more effective than fixed-pitch wind turbines at optimizing electrical power output due to the ability of variable-pitched wind turbines to start spinning at a high pitch and then decrease the pitch to optimize power output.

28. Results/Conclusions: Overview • A fixed-pitch turbine is like a 21-speed bike stuck in one gear: It is either hard to get moving, or it will not move fast. A variable-pitch turbine can “switch gears” to take better advantage of drag, lift, and varying winds, and it is therefore about three times more powerful.