Introduction to Wind Energy
Division of Mechanical Engineering Takaaki Kono
January 16, 2025
1. Basics of Wind Energy
2. Pros and Cons of Wind Energy Short test
Outline
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What is the cause of wind?
・Wind gets its start from the sun.
・When the sun shines down on the earth, the surface of the earth is heated.
・ Because the earth’s surface is made up of different
formations, including land and water, the sun heats the earth unevenly.
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What is the cause of wind?
・As the different surfaces heat up, the hot air rises and cooler air comes in to fill the void.
→ Wind near the earth’s surface
・The air above the land heats up faster than the air above the water.
・When the hot air above the land rises, the cooler air from the water rushes ashore.
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1. The kinetic energy that the flow of air has.
What is wind energy?
1 2
2 mU
Amount of kinetic energy that air with a mass of m kg and with a velocity of U m/s has is:
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1. The energy that the flow of air has.
2. The process or ability by which wind is used to generate mechanical power or electricity.
What is wind energy?
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History of wind energy
・The first reported use of wind energy was to power boats as early as 5000 BCE.
・Wind mills were put into use around the 11th century CE for pumping water and grinding flour.
・The first wind turbine specifically used to produce electricity was built in 1887 in Glasgow, Scotland.
Halnaker windmill,
constructed in the UK c.1780 First wind turbine 7/32
How does a wind turbine make electricity?
Sufficiently strong wind
Aerodynamic force on blades (A) occur and blades and hub (B) rotate
C A
A A
B D G
Rotor (A+B) spins the Shaft (C) and gears in the gear box(D), which spin the generator (G), resulting in
electrical output
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How aerodynamic force on blades rotate rotor?
Relative wind velocity
Relative rotational wind velocity
Wind velocity
Rotational plane
Wind velocity
・Cross section of a blade has an airfoil shape.
・Relative wind velocity flows into the airfoil is the resultant velocity of wind velocity and relative rotational wind
velocity.
Rotational velocity
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Relative wind
velocity Lift force
Drag force
Rotational plane
・Depending on the relative wind velocity, high pressure side and low pressure side are formed on the airfoil.
・Lift force acts on the airfoil in the vertical direction to the relative wind velocity.
・Drag force acts on the airfoil in the same direction to the relative wind velocity.
Relative wind velocity
High pressure side Low pressure side
How aerodynamic force on blades rotate rotor?
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Relative wind velocity
Rotational relative wind velocity
Wind velocity
Lift force Drag force
Rotational plane
・Resultant force in the rotational direction is obtained by adding the component of lift force in the rotational
direction and the component of drag force in the rotational direction.
・Due to the resultant force in the rotational direction, the rotor rotates.
Lift force
Drag force
Rotational plane Rotational plane
+ =
How aerodynamic force on blades rotate rotor?
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Available wind power
= = 1 2 = 1 2
( )
2 2
w
dE dm
P U AU U
dt dt
Amount of kinetic energy that air with a mass of m kg and with a velocity of U m/s has is:
= 1 2
( )
2mU E
U
A(=D2/4)
D
Amount of mass that the air with a density of ρ kg /m3 and with a velocity of U m/s passes through the rotor area A per unit time is:
(= dm ) AU dt
Amount of wind power that the air with a density of ρ kg /m3 and with a velocity of U m/s passes through the rotor area A per unit time is:
Wind power [W]: Amount of wind energy transmitted per unit time
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Wind power and wind velocity
U
A(=D2/4)
D
= 1
3=
2
32 8
P
wAU D U
By substituting A=
D2/4, wind power is expressed as２ ３
= 1
2( )
w
2
P AU U
Amount of wind power that the air with a density of ρ kg /m3 and with a velocity of U m/s passes through the rotor area A per unit time is:
Wind power: A rate at which wind energy is transmitted
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Mean annual wind speed map
http://app8.infoc.nedo.go.jp/nedo/
Wind speed [m/s]
Area where mean wind speed is high：
・Offshore area
・Costal area
・Mountainous area in
Hokkaido and Tohoku district
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Wind profile and terrain roughness
・Wind speed decreases with decrease in the distance from the ground.
・As the terrain roughness becomes higher due to buildings and trees, the momentum of wind is lost more and wind velocity decreases.
So, wind speed in the offshore and coastal areas is high.
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Wind characteristics in mountainous area
・Near the crest of the ridge, the wind speed is accelerated.
・In the leeward of the ridge, highly turbulent zone is formed.
Highly turbulent wind causes the greater structural loading of a turbine and increases the possibility of it’s failures.
To prevent the failures, the structural strength of the turbine needs to be designed sufficiently high, and this leads to high cost.
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Operation of wind turbine generation system
・Cut-in wind speed: Lowest wind speed at which the system produces power output
・Rated wind speed：The system’s rated power is achieved.
（Above the wind speed, the power output is controlled to be constant）
・Cut-out wind speed: Highest wind speed at which the system is designed to produce power
Wind speed
Stopped Partial load operation Rated power operation Stopped
Power output Rated wind speed Cut-out wind speed
Cut-in wind speed
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Representative sizes of wind turbines with different rated power
= 1
3=
2
32 8
P
WAU D U
２・Wind power utilized by a wind turbine is proportional to square of the rotor diameter.
・The sizes of wind turbines are increasing year by year.
・A 10 MW class wind turbine (V164 MHI Vestas) has a rotor diameter of 164 m.
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Offshore wind turbines
Since the wind speed is higher in the offshore areas, the Japanese government aims to generate up to 45 gigawatts of power through offshore wind power by 2040, a level that would make the country the world’s third-largest generator of such power, as part of efforts to achieve net zero emissions of carbon dioxide by 2050.
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Offshore wind turbines
Two types of offshore wind turbines:
・Bottom mounted type: appropriate for relatively shallow sea area.
・Floating type: Appropriate for relatively deep sea area.
Since the available areas for the bottom mounted type are limited in Japan, the floating type will be dominant in the future.
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Outline
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1. Basics of Wind Energy
2. Pros and Cons of Wind Energy
Short test
Advantages of wind energy
1. No greenhouse gas (GHG) production during operation
Operation
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Advantages of wind energy
1. No greenhouse gas (GHG) production during operation
→Life cycle GHG emission estimates are very low
Onshore
Offshore
Nana Yaw Amponsah et al.,Greenhouse gas emissions from renewable energy sources: A review
of lifecycle considerations, Renewable and Sustainable Energy Reviews, Volume 39, 2014 23/32
Advantages of wind energy
2. Almost no limit as long as sunshine reaches to the Earth.
Reason: Wind is created by temperature changes in the atmosphere. As warm air rises, cool air moves into the area, and the movement creates wind.
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Advantages of wind energy
3. Many jobs are created in the wind energy industry.
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Advantages of wind energy
3. Many jobs are created in the wind energy industry.
→In addition to manufacturers and developers,
installation, repair and O&M of wind turbines have a large share of employment.
Direct employment by type of company,
according to EWEA survey, source EWEA, 2008.
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Advantages of wind energy
4. Levelized cost of electricity (LCOE) of onshore wind is the lowest among other utility-scale renewable power generation technologies
LCOE: a measure of the average net present cost of electricity
generation for a generator over its lifetime
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Advantages of wind energy
5. Land surrounding wind turbines can still be used for farming, etc.
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Disadvantages of wind energy
1. Wind is inconsistent and unpredictable
Rated power (1,100kW)
(hour)
Generated electricity by a wind turbine
Time
Often necessary to work with other energy generation systems, including those that use fossil fuels, or energy storage systems.
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Disadvantages of wind energy
2. Wind turbine noise
→Rotating blades generate noise that is annoying to someone who lives near by
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Disadvantages of wind energy
3. Visual impact
→ Some people find wind turbines
visibly unappealing.
4. Bird strike
→Rotating blades hurt or kill birds including endangered species.
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Disadvantages of wind energy
5. NIMBY (not in my back yard)
→ There are opponents to installation of wind turbines who like the idea of energy generation by the wind, but do not want the wind turbines in their area.
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Thank you for your attention!!
