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

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

Galen Maly . Yorktown High School. Investigating the Use of a Variable-Pitch Wind Turbine to Optimize Power Output Under Varying Wind Conditions. Background. In 2001, 0.15 percent of electricity consumed in the U.S. came from wind turbines.

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Presentation Transcript

Galen Maly

Yorktown High School

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

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.
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.
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.
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.
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
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.
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.
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.
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.
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.
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.
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.
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.
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
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.
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.
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.
Results/Conclusions: Objective 1

Effect of Wind Speed on Power Output Using Fixed-Pitch and Programmed Variable-Pitch Blades

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.
Results/Conclusions: Objective 3

Effect of Varying Blade Pitch on Power Output When Wind Speed is Constant (6.3 m/s)

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.
Results/Conclusions: Objective 4

Effect of Wind Speed on Power Output Using Fixed-Pitch and Programmed Variable-Pitch Blades

Results/Conclusions: Objective 4

Effect of Wind Speed on Optimum Pitch

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.
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.
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.