Laboratory 2 Questions
Wind Energy Conversion
123456-
What is a wind turbine? Please, define in two lines. Here it is ask the only the concept.
Why it is important? Why this new trend in research and invest in wind energy?
How it works?
How do wind turbines produce electricity?
How it is composed?
What can you do with a wind turbine? Can you use the wind energy directly from the wind
turbine? What are the disadvantages of the wind energy?
7- How a wind turbine system works?
8- How is the curve of a wind turbine? (Power output vs speed)
1. What is a wind turbine?
It is a device that transforms kinetic energy from the wind into electrical energy.
2. Why it is important?
This trend is due to the level of pollution that the current generation systems are producing. In
fact, It is also one of the most polluting of all industries, responsible for :
• 3/4 three-fourths of U.S. sulfur oxides (SOX) emissions
• 1/3 one-third of our carbon dioxide (CO2) and nitrogen oxides (NOX) emissions
• 1/4 one-fourth of particulate matter and toxic heavy metals emissions.
Just in USA.
The main reason is the cost of fossil fuel are increasing as they are scarcing.
3. How it works?
The air is a fluid in which the particles are in gas form instead of liquid. When air moves
quickly, in the form of wind, the particles are moving quickly. Motion means kinetic energy
which can be captured just like the energy in moving water in a hydroelectric dam.
In the case of wind electric turbine; the turbine blades capture the kinetic energy in the wind.
When the blades capture the wind energy, they start moving; they spin a shaft that leads from
the hub of the rotor to a generator.
The generator turns/transform the rotational energy to electrical energy.
4. How do wind turbines produce electricity?
The wind turbine works the opposite of a fan
5. How it is composed?
Anemometer: Measures the wind speed and transmits wind speed data to the controller.
Blades: Lifts and rotates when wind is blown over them, causing the rotor to spin. Most
turbines have either two or three blades.
Brake: Stops the rotor mechanically, electrically, or hydraulically, in emergencies.
Controller: Starts up the machine at wind speeds of about 8 to 16 miles per hour (mph) and
shuts off the machine at about 55 mph. Turbines do not operate at wind speeds above about 55 mph
because they may be damaged by the high winds.
Gear box: Connects the low-speed shaft to the high-speed shaft and increases the rotational
speeds from about 30-60 rotations per minute (rpm), to about 1,000-1,800 rpm; this is the rotational
speed required by most generators to produce electricity. The gear box is a costly (and heavy) part of
the wind turbine and engineers are exploring "direct-drive" generators that operate at lower rotational
speeds and don't need gear boxes.
Generator: Produces 60-cycle AC electricity; it is usually an off-the-shelf induction
generator.
High-speed shaft: Drives the generator.
Low-speed shaft: Turns the low-speed shaft at about 30-60 rpm.
Nacelle: Sits atop the tower and contains the gear box, low- and high-speed shafts, generator,
controller, and brake. Some nacelles are large enough for a helicopter to land on.
Pitch: Turns (or pitches) blades out of the wind to control the rotor speed, and to keep the
rotor from turning in winds that are too high or too low to produce electricity.
Rotor: Blades and hub together form the rotor.
Tower: Made from tubular steel (shown here), concrete, or steel lattice. Supports the structure
of the turbine. Because wind speed increases with height, taller towers enable turbines to capture
more energy and generate more electricity.
Wind direction: Determines the design of the turbine. Upwind turbines—like the one shown
here—face into the wind while downwind turbines face away.
Wind vane: Measures wind direction and communicates with the yaw drive to orient the
turbine properly with respect to the wind.
Yaw drive: Orients upwind turbines to keep them facing the wind when the direction
changes. Downwind turbines don't require a yaw drive because the wind manually blows the rotor
away from it.
Yaw motor: Powers the yaw drive.
6. What can you do with a wind turbine? Can you use the wind energy directly from the wind
turbine? What are the disadvantages of the wind energy?
The kinetic energy from the wind is varying and there is no way to predict its exact behoavior. Then,
the power produce by the wind turbine is also variable. The same problem of PV panels. I need a
Wind Energy System to stabilize the voltage or current to use my loads.
Problem with wind power:
- Wind farms must be installed on large tracts of lands or along coastlines to capture the
greatest wind movement. Sometimes they make conflict with other priorities such as
agriculture, urban development or water front views from expansions located in prime
location.
- Expensive
Dato curioso:
Europe Union has 48% of world’s installed wind power capacity.
7. How a wind turbine system works?
See class.
8. How is the curve of a wind turbine? (Power output vs speed)
Wind turbine power output variation with steady wind
Cut in speed:
Very low speed are dangerous due to the resonance frequency of the tower. Buildings has a
very low resonance frequency, when some external source of energy produce this
frequencies, the system resonates and can collapse.
Rated output power and wind speed:
As wind speed rises the cut in speed the Power increase rapidly and Power reaches that limit
of the generator. The limit is made through adjusting blades.
Cut off:
If speed increases above rate output wind speed then the forces on the turbine
structure increase there is a risk to damage rotor. Then, braking system is employed to bring
the rotor to stop.
Types of Control:
In the beginning of the characteristic curve, the control system uses MPPT to track
the maximum wind energy until it reaches to the rated output power of the generator. After
that it changes the control to CONSTANT POWER CONTROL. It keeps the power
constant even when the wind speed increases.
Report on Wind Experiment
Answer the following questions in two pages (printed format).
1- Explain the operation of wind turbine?
2- Explain why the AC output of the wind turbine cannot be utilized directly? Explain how
do power electronics help to handle this problem?
3- Explain why the wind blade cannot be directly connected to the wind generator?
4- Choose one of the already built wind plants all over the world and describe it briefly.
Hint: The student should refer to the website of the U.S. Department of Energy Efficiency and Renewable Energy at the link: www1.eere.energy.gov/wind/wind how.html and National Renewable Energy Laboratory at the link: http://www.nrel.gov.