ECE 566: Grid Integration of Wind Energy Systems S. Suryanarayanan - - PowerPoint PPT Presentation

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

ECE 566: Grid Integration of Wind Energy Systems

• S. Suryanarayanan

Associate Professor ECE Dept.

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

Reminders and notifications

1

Homework 1: Due on 9.9.2014 at 515pm (mtn time) via RamCT Blackboard.

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

Reminders and notifications

1

Homework 1: Due on 9.9.2014 at 515pm (mtn time) via RamCT Blackboard.

2

Due to my travel engagement, the first half of the lecture (from 515pm-630pm) on 9.9.2014 is canceled.

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

Reminders and notifications

1

Homework 1: Due on 9.9.2014 at 515pm (mtn time) via RamCT Blackboard.

2

Due to my travel engagement, the first half of the lecture (from 515pm-630pm) on 9.9.2014 is canceled.

3

The second half of the lecture (from 645pm-8pm Mtn time) on 9.9.2014 is as scheduled. You are expected to attend the second half of the lecture.

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

Reminders and notifications

1

Homework 1: Due on 9.9.2014 at 515pm (mtn time) via RamCT Blackboard.

2

Due to my travel engagement, the first half of the lecture (from 515pm-630pm) on 9.9.2014 is canceled.

3

The second half of the lecture (from 645pm-8pm Mtn time) on 9.9.2014 is as scheduled. You are expected to attend the second half of the lecture.

4

In lieu of the cancellation of the first half, you will be required to view a seminar on the topic. Link and other information will be provided via RamCT Blackboard.

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

From the Week-1 reading material

1

What is the expression for maximum possible power extraction from the wind stream?

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

From the Week-1 reading material

1

What is the expression for maximum possible power extraction from the wind stream?

2

What is the maximum power coefficient termed as and what is its numeric value?

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

From the Week-1 reading material

1

What is the expression for maximum possible power extraction from the wind stream?

2

What is the maximum power coefficient termed as and what is its numeric value?

3

What is the practical achievable value of this coefficient?

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

From the Week-1 reading material

1

What is the expression for maximum possible power extraction from the wind stream?

2

What is the maximum power coefficient termed as and what is its numeric value?

3

What is the practical achievable value of this coefficient?

4

What is the definition of tip-speed ratio?

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

From the Week-1 reading material

1

What is the expression for maximum possible power extraction from the wind stream?

2

What is the maximum power coefficient termed as and what is its numeric value?

3

What is the practical achievable value of this coefficient?

4

What is the definition of tip-speed ratio?

5

How do the TSR and the blade pitch angle affect the power coefficient?

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

From the Week-1 reading material

1

What is the expression for maximum possible power extraction from the wind stream?

2

What is the maximum power coefficient termed as and what is its numeric value?

3

What is the practical achievable value of this coefficient?

4

What is the definition of tip-speed ratio?

5

How do the TSR and the blade pitch angle affect the power coefficient?

6

What is the definition of capacity factor (CF)? Qualitatively compare the CFs of a nuclear power plant and a wind power plant?

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References Cp v. λ P(MW) v. ω Wind velocities v. tower height [2] In-class problem

Cp v. λ (Figure from: [1])

For MOD-2 type turbine

1 β = 1 λ+0.08θ − 0.035 1+θ3

Cp(λ, θ) = C1(C2 1

β − C3θ − C4θx − C5)e −C6 1 β

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References Cp v. λ P(MW) v. ω Wind velocities v. tower height [2] In-class problem

P(MW) v. ω (Figure from: [1])

For MOD-2 type turbine

λ = ωw R

υ1 1 β = 1 λ+0.08θ − 0.035 1+θ3

Cp(λ, θ) = C1(C2 1

β − C3θ − C4θx − C5)e −C6 1 β

Red line represents the maximum power extraction curve. Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References Cp v. λ P(MW) v. ω Wind velocities v. tower height [2] In-class problem

How does tower height affect wind velocities?

Wind speeds differ from blades nearest to the ground and the blades at the top of the rotation This may produce flow and power effects on the turbine When wind speeds lie in the operational range of the turbine and exceed 4m/s, the formula for wind speed at height h is: υw(h) = υ10 ( h

h10 )a

where, υ10 is the wind speed measured at 10m For onshore wind farms, typical values of the Hellman exponent, a is: | 0.14 ≤ a ≤ 0.17

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References Cp v. λ P(MW) v. ω Wind velocities v. tower height [2] In-class problem

The Hellman exponent [3]

The Hellman exponent, a, quantifies variation of wind speed with height a depends on:

1

coastal location

2

terrain shape on the ground

3

air stability.

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References Cp v. λ P(MW) v. ω Wind velocities v. tower height [2] In-class problem

The Hellman exponent: Example values from [3]

Location Hellman exponent Unstable air above open water surface 0.06 Neutral air above open water surface 0.1 Unstable air above flat open coast 0.11 Neutral air above flat open coast 0.16 Stable air above open water surface 0.27 Unstable air above human inhabited areas 0.27 Neutral air above human inhabited areas 0.34 Stable air above flat open coast 0.4 Stable air above human inhabited areas 0.6

For more on types of air, see [4]. Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References Cp v. λ P(MW) v. ω Wind velocities v. tower height [2] In-class problem

Hellman exponent a=0.16 for υ30 v. υ10 [2]

2 4 6 8 10 12 2 4 6 8 10 12

υ1 0 υ30 Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References Cp v. λ P(MW) v. ω Wind velocities v. tower height [2] In-class problem

Vertical profile effects on turbines [2], [5]

First approximations

Figure shows variation of wind speed with tower height for υ10 = 9 m/s. First approximations: You may assume r=0.7R (i.e., 70% of rotor radius) for

• calc. purposes.

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References Cp v. λ P(MW) v. ω Wind velocities v. tower height [2] In-class problem

In-class problem For a MOD-2 type turbine with 80m blade diameter, the wind velocity measured at a height of 10 m is 4.9 m/s. If the blades are making 20 rotations per minute and the pitch angle is 1◦, find the power generated by this turbine. Use the following given values: C1 : C6 = [0.5 116 0.4 0.022 5.6 21], x = 1.5, and ρ = 1.23 kg/m3.

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References Cp v. λ P(MW) v. ω Wind velocities v. tower height [2] In-class problem

In-class problem: Solution Find the rotor length for which we can assume steady state wind conditions thru first approximations: r = (Rotord/2) ∗ 0.7 = 28m

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References Cp v. λ P(MW) v. ω Wind velocities v. tower height [2] In-class problem

In-class problem: Solution Find the rotor length for which we can assume steady state wind conditions thru first approximations: r = (Rotord/2) ∗ 0.7 = 28m If υ10 = 4.9m/s, υ28 = υ10 ∗ r

10 0.16 = 5.77m/s

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References Cp v. λ P(MW) v. ω Wind velocities v. tower height [2] In-class problem

In-class problem: Solution Find the rotor length for which we can assume steady state wind conditions thru first approximations: r = (Rotord/2) ∗ 0.7 = 28m If υ10 = 4.9m/s, υ28 = υ10 ∗ r

10 0.16 = 5.77m/s

If the blades are turning at 20 rpm, then ωw = 2∗π∗20

60

= 2.09rad/s, and λ = ωw∗Rotord

2∗υ28

= 14.52

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References Cp v. λ P(MW) v. ω Wind velocities v. tower height [2] In-class problem

In-class problem: Solution Find the rotor length for which we can assume steady state wind conditions thru first approximations: r = (Rotord/2) ∗ 0.7 = 28m If υ10 = 4.9m/s, υ28 = υ10 ∗ r

10 0.16 = 5.77m/s

If the blades are turning at 20 rpm, then ωw = 2∗π∗20

60

= 2.09rad/s, and λ = ωw∗Rotord

2∗υ28

= 14.52

1 β = 1 λ+0.08θ − 0.035 1+θ3 for λ = 14.52 and θ = 1 is 0.0511

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References Cp v. λ P(MW) v. ω Wind velocities v. tower height [2] In-class problem

In-class problem: Solution Cp(14.52, 1) = 0.5(116 1

β − 0.4θ − 0.002θ1.5 − 5.6)e−21 1

β = −0.0164 Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References Cp v. λ P(MW) v. ω Wind velocities v. tower height [2] In-class problem

In-class problem: Solution Cp(14.52, 1) = 0.5(116 1

β − 0.4θ − 0.002θ1.5 − 5.6)e−21 1

β = −0.0164

P = Cp ∗ ρ ∗ π ∗ R2 ∗ υ3

28 ∗ 0.5 = −9756.5 kW

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References Cp v. λ P(MW) v. ω Wind velocities v. tower height [2] In-class problem

In-class problem: Solution Cp(14.52, 1) = 0.5(116 1

β − 0.4θ − 0.002θ1.5 − 5.6)e−21 1

β = −0.0164

P = Cp ∗ ρ ∗ π ∗ R2 ∗ υ3

28 ∗ 0.5 = −9756.5 kW

Typically, for negative Cp values, wind turbine controllers are set to produce 0 electricity.

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References Types of wind turbines Horizontal-axis wind turbine (HAWT) Vertical-axis wind turbine (VAWT)

Types of wind turbines [6]

Horizontal-axis wind turbine (HAWT): Where the main rotor and the electric generator are pointed in the (upwind or downwind) direction of the wind. Vertical-axis wind turbine (VAWT): Where the rotor blades are arranged vertically to capture wind blowing in any direction.

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References Types of wind turbines Horizontal-axis wind turbine (HAWT) Vertical-axis wind turbine (VAWT)

Horizontal-axis wind turbine (HAWT). Fig. from [7]

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References Types of wind turbines Horizontal-axis wind turbine (HAWT) Vertical-axis wind turbine (VAWT)

Horizontal-axis wind turbine (HAWT) [6], [2]

For small rating HAWT, wind vanes are used to point blades in wind direction For larger HAWT, servo-controlled motors are used for

• rienting blades in wind direction

For larger HAWT, blade lengths vary from 20-40 meters

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References Types of wind turbines Horizontal-axis wind turbine (HAWT) Vertical-axis wind turbine (VAWT)

Horizontal-axis wind turbine (HAWT) [6], [2]

TSR (λ) is a critical measure for determining blade dimensions . Since, λ = (υw)R

υ1

, large machines have low rotational speeds and vice-versa kW rated machines reach speeds of 180 rpm MW rated machines reach speeds of 20 rpm

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References Types of wind turbines Horizontal-axis wind turbine (HAWT) Vertical-axis wind turbine (VAWT)

Vertical-axis wind turbine (VAWT) [6]

Used in cases where the wind direction changes frequently Sub-types include: Darrieus, Giromill, Savonius, and twisted-Savonius Darrieus or egg-beaters with curved blades have good η but poor reliability due to high cyclical stress; they have low starting torques and may need external sources to start turning. Giromill uses the Darrieus construction with straight blades. Advantages include self-staring, higher starting torque, higher Cp, higher η in turbulent winds, lower TSR for reduced blade stresses.

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References Types of wind turbines Horizontal-axis wind turbine (HAWT) Vertical-axis wind turbine (VAWT)

Darrieus and Giromill types VAWT. Figs. from [8], [9]

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References Types of wind turbines Horizontal-axis wind turbine (HAWT) Vertical-axis wind turbine (VAWT)

Vertical-axis wind turbine (VAWT) [6]

Savonius type uses scoops such as on anemometers and are used in high reliability, lower efficiency turbines. When three or more scoops are present, the Savonius type is self-starting. Twisted-Savonius has long helical scoops for smoother torques for use in rooftops.

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References Types of wind turbines Horizontal-axis wind turbine (HAWT) Vertical-axis wind turbine (VAWT)

Savonius and twisted-Savonius types VAWT. Figs. from [10], [11]

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References Types of wind turbines Horizontal-axis wind turbine (HAWT) Vertical-axis wind turbine (VAWT)

Comapring HAWT and VAWT. Fig. from [12]

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References Types of wind turbines Horizontal-axis wind turbine (HAWT) Vertical-axis wind turbine (VAWT)

Cp v. λ for wind turbine types [2], fig. from [13]

Darrieus and fast two-blades are high-speed rotors with aerodynamic blades American multi-blade and Dutch 4-blade with non-aerodynamic blades have lower Cp Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

Parts of a wind turbine. Fig. from [14]

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

Parts of a wind turbine [14] Tower: Since wind speeds are higher at greater heights, tubular towers made of concrete or steel are used for supporting the wind turbine structure

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

Parts of a wind turbine [14] Tower: Since wind speeds are higher at greater heights, tubular towers made of concrete or steel are used for supporting the wind turbine structure Blades: When wind blows over them, they lift and rotate causing the rotor to spin. Together with the hub, blades form the rotor

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

Parts of a wind turbine [14] Tower: Since wind speeds are higher at greater heights, tubular towers made of concrete or steel are used for supporting the wind turbine structure Blades: When wind blows over them, they lift and rotate causing the rotor to spin. Together with the hub, blades form the rotor Pitch control: Used for controlling the rotor speed when wind speeds change by turning (or pitching) blades. The rotor will stop turning in winds that are too high or too low to produce electricity

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

Parts of a wind turbine [14] Tower: Since wind speeds are higher at greater heights, tubular towers made of concrete or steel are used for supporting the wind turbine structure Blades: When wind blows over them, they lift and rotate causing the rotor to spin. Together with the hub, blades form the rotor Pitch control: Used for controlling the rotor speed when wind speeds change by turning (or pitching) blades. The rotor will stop turning in winds that are too high or too low to produce electricity Brakes: Used to stop the rotor during emergencies

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

Parts of a wind turbine (contd.) [14] Shafts & gearbox: Low-speed shaft turns at 30 − 60 rpm and captures the rotational energy of the rotor. This speed is not optimal for driving the induction generator for producing electricity. So, a gearbox is used for converting low-speed rotation to high-speed rotation at 1000 − 8000

• rpm. The high-speed shaft then drives the induction

generator

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

Parts of a wind turbine (contd.) [14] Shafts & gearbox: Low-speed shaft turns at 30 − 60 rpm and captures the rotational energy of the rotor. This speed is not optimal for driving the induction generator for producing electricity. So, a gearbox is used for converting low-speed rotation to high-speed rotation at 1000 − 8000

• rpm. The high-speed shaft then drives the induction

generator Generator: An induction machine for producing electric energy at 60 Hz frequency

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

Parts of a wind turbine (contd.) [14] Controller: Taking information from the anemometer on wind direction and speed, a controller will start and shut-off the machine at certain speeds.

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

Parts of a wind turbine (contd.) [14] Controller: Taking information from the anemometer on wind direction and speed, a controller will start and shut-off the machine at certain speeds. Nacelle: The cocoon-shaped housing in which the shafts, gearbox, generator, and controller are located.

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

Parts of a wind turbine (contd.) [14] Controller: Taking information from the anemometer on wind direction and speed, a controller will start and shut-off the machine at certain speeds. Nacelle: The cocoon-shaped housing in which the shafts, gearbox, generator, and controller are located. Yaw drive & motor: Housed at the base of the nacelle on the tower top, these are used to orient the blades in the up

• r down directions to upwind.

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

Parts of a wind turbine (contd.) [14] Controller: Taking information from the anemometer on wind direction and speed, a controller will start and shut-off the machine at certain speeds. Nacelle: The cocoon-shaped housing in which the shafts, gearbox, generator, and controller are located. Yaw drive & motor: Housed at the base of the nacelle on the tower top, these are used to orient the blades in the up

• r down directions to upwind.

Animation from US DOE EERE:http://energy.gov/ eere/wind/how-does-wind-turbine-work

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

Typical power curves [15]

Typical power curves [15] Cut-in speed: Due to low torques at low wind speeds, wind turbines do not begin to rotate and generate electricity until a certain minimum wind speed, υmin, of approximately 3 − 4 m/s is reached.

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

Typical power curves [15]

Typical power curves [15] Cut-in speed: Due to low torques at low wind speeds, wind turbines do not begin to rotate and generate electricity until a certain minimum wind speed, υmin, of approximately 3 − 4 m/s is reached. Rated speed: As wind speeds climb over υmin, the power produced rises rapidly as a cubic function up to the rated power output. The rated power output is usually reached at 12 − 17 m/s wind speed, and sustained till 23 − 25 m/s by means of pitch and yaw controls.

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

Typical power curves [15]

Typical power curves [15] Cut-out speed: As wind speeds increase further, the torque on the machine may induce stress on the structure and cause damage to the rotor. To prevent this, a braking mechanism is used to stall or stop the rotor and bring it to a standstill at the cut-out speed, υmax, of approximately 25 m/s.

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

Typical power curves. Fig. from [15]

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

Typical power curves [16]

Typical power curves [16] Hysteresis: When wind speeds drop below υmax, the wind turbine does not immediately start generating electricity. Instead, depending upon the wind profile and the control technology used (pitch, yaw, stall), the wind turbine will restart operation. The restart, known as the hysteresis loop, usually requires a reduction from υmax of 3 − 4 m/s

• nly.

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

Typical power curves. Fig. from [17]

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

Typical power curves [16]

Typical power curves [16] In geographically distributed wind farms, the effect of hysteresis may be smaller on the grid output. In other cases, the output fluctuation is significant. This is particularly significant in situations of dramatic weather conditions such as a storm. To minimize the effect of such sudden loss of large supply, manufacturers provide wind turbines with power curves that reduce power production in a step-wise fashion with increase in wind speeds.

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

Power curve for a pitch-regulated 1.5 MW wind turbine. Fig. from [16]

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

Power fluctuations in wind farms [2] We know that wind speed varies with height and this causes fluctuations in the power production. Note, Hellman exponent.

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

Power fluctuations in wind farms [2] We know that wind speed varies with height and this causes fluctuations in the power production. Note, Hellman exponent. Power fluctuations also cause variations in the torque during blade rotation

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

Power fluctuations in wind farms [2] We know that wind speed varies with height and this causes fluctuations in the power production. Note, Hellman exponent. Power fluctuations also cause variations in the torque during blade rotation Other factors that cause power fluctuations are:

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

Power fluctuations in wind farms [2] We know that wind speed varies with height and this causes fluctuations in the power production. Note, Hellman exponent. Power fluctuations also cause variations in the torque during blade rotation Other factors that cause power fluctuations are:

1

Tower wind-shadow: HAWT towers obstruct the airflow and affect the streamline of wind by decreasing its axial speed.

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

Power fluctuations in wind farms [2] We know that wind speed varies with height and this causes fluctuations in the power production. Note, Hellman exponent. Power fluctuations also cause variations in the torque during blade rotation Other factors that cause power fluctuations are:

1

Tower wind-shadow: HAWT towers obstruct the airflow and affect the streamline of wind by decreasing its axial speed.

2

Number of blades

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

Power fluctuations in wind farms [2] We know that wind speed varies with height and this causes fluctuations in the power production. Note, Hellman exponent. Power fluctuations also cause variations in the torque during blade rotation Other factors that cause power fluctuations are:

1

Tower wind-shadow: HAWT towers obstruct the airflow and affect the streamline of wind by decreasing its axial speed.

2

Number of blades

3

Positioning of turbine in upwind or downwind direction

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

Power fluctuations in wind farms [2] We know that wind speed varies with height and this causes fluctuations in the power production. Note, Hellman exponent. Power fluctuations also cause variations in the torque during blade rotation Other factors that cause power fluctuations are:

1

Tower wind-shadow: HAWT towers obstruct the airflow and affect the streamline of wind by decreasing its axial speed.

2

Number of blades

3

Positioning of turbine in upwind or downwind direction

4

General surroundings

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

Power fluctuations in wind farms [2] In symmetrically arranged multi-blade turbines, assuming that the wind conditions are identical for all blades, the torque experienced by transmission shaft is somewhat constant.

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

Power fluctuations in wind farms [2] In symmetrically arranged multi-blade turbines, assuming that the wind conditions are identical for all blades, the torque experienced by transmission shaft is somewhat constant. However, due to existing Cp–λ characteristics, further power/torque fluctuations arise in the drive train.

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

Power fluctuations in wind farms [2] Represented as: M(ψ) = Mu − 1

z [(Mo(zωt)]

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

Power fluctuations in wind farms [2] Represented as: M(ψ) = Mu − 1

z [(Mo(zωt)]

where: M(ψ) is pitch dependent torque; Mu is torque under undisturbed wind distribution; Mo is the oscillating component; z is the number of rotor blades.

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

Aggregation in the wind farm

Increased number of wind turbines in a wind farm [16]. Fig. from [16] ⇑ wind turbines in a wind farm ⇓ the impact of the turbulent peak Not all wind turbines experience wind gusts at the same time Ideally, % of variation in Pout ⇓ as n

−1 2 , for n wind turbines.

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

Percentage variation of power output with increase in wind turbines

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

Aggregation in the wind farm

Distribution of wind turbines in a wind farm [16]

When wind turbines are spatially distributed, the impact of synoptic and diurnal peaks are reduced

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

Aggregation in the wind farm

Distribution of wind turbines in a wind farm [16]

When wind turbines are spatially distributed, the impact of synoptic and diurnal peaks are reduced This is due to changing weather patterns affecting wind turbines differently

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

Aggregation in the wind farm

Distribution of wind turbines in a wind farm [16]

When wind turbines are spatially distributed, the impact of synoptic and diurnal peaks are reduced This is due to changing weather patterns affecting wind turbines differently Effects of varying wind speeds and associated cut-out or hysteresis are diluted in large wind farm

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

Aggregation in the wind farm

Distribution of wind turbines in a wind farm [16]

Also, the maximum (up and down) ramp rates are slower for dispersed wind farms

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

Aggregation in the wind farm

Distribution of wind turbines in a wind farm [16]

Also, the maximum (up and down) ramp rates are slower for dispersed wind farms

Maximum ramp rate for a 1000 MW wind farm with dispersed clusters of 10 − 20 MW can be 6.6 MW/min

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

Aggregation in the wind farm

Distribution of wind turbines in a wind farm [16]

Also, the maximum (up and down) ramp rates are slower for dispersed wind farms

Maximum ramp rate for a 1000 MW wind farm with dispersed clusters of 10 − 20 MW can be 6.6 MW/min Maximum ramp rate for a 200 MW single wind farm can be ≥ 20 MW/min

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

• Fig. from [16]

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

Dionysios C. Aliprantis. Fundamentals of Wind Energy Conversion for Electrical Engineers. URL: http://goo.gl/sHHZMU (visited on 08/29/2014).

• S. Heier. Grid Integration of Wind Energy: Onshore and

Offshore Conversion Systems. Wiley, 2014. ISBN: 9781118703304. Wind gradient: Wind turbines. Wikipedia. URL: http://en.wikipedia.org/wiki/Wind_ gradient#Wind_turbines (visited on 07/25/2014).

• M. Jenkins. Atmospheric Stability And Instability. Utah

State University, WILD4520 - Wildland Fire Management and Planning, Spring 2004 course. URL: http://goo.gl/A1PyWa (visited on 2008).

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

The Swiss Wind Power Data Website. Wind Profile

• Calculator. URL:

http://wind-data.ch/tools/profile.php?h= 10&v=8.5&z0=0.1&abfrage=Refresh (visited on 08/29/2014). Wind turbine. Wikipedia. URL: http://goo.gl/NIrw. Michael Bloch. Electricity from the wind – how turbines

• work. Green Living Tips. URL:

http://goo.gl/qp08kE (visited on 07/02/2008). Darrieus-windmill. Licensed under Public domain via Wikimedia Commons. URL: http://goo.gl/hp8wkH (visited on 09/01/2014).

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

Vertical Axis Wind Turbine Darrieus Giromill WG-1K5 1

• kW. 2020 Solar Clean Technology. URL:

http://www.2020solar.com/WG-1K5-95.asp (visited on 09/01/2014). Technology solutions for wind power generated

• electricity. Green Energy Reporter. URL:

http://goo.gl/nJFC6v (visited on 2013). Small Wind Turbines. National Renewable Energy Centre, UK. URL: http://goo.gl/f64H0n (visited on 2014). Wind basics. Hill Country Wind Power. URL: http://www.hillcountrywindpower.com/wind- basics.php (visited on 09/01/2014).

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

• A. M. Ragheb M. Ragheb. Fundamental and Advanced

Topics in Wind Power. Ed. by R. Carriveau. InTech,

• 2011. Chap. Wind Turbines Theory - The Betz Equation

and Optimal Rotor Tip Speed Ratio. The Inside of a Wind Turbine. US Dept. of Energy EERE.

URL: http://energy.gov/eere/wind/inside-

wind-turbine-0 (visited on 09/01/2014). Wind turbine power ouput variation with steady wind

• speed. WindPower Program. URL:

http://www.wind-power- program.com/turbine_characteristics.htm (visited on 09/01/2014).

Suryanarayanan ECE 566 Lecture/Week 2

Physics of wind power Wind turbines Parts of a wind turbine Typical power curves Power fluctuations in wind farms Aggregation in the wind farm References

• T. Ackermann. Wind Power in Power Systems. Wiley,
• 2012. ISBN: 9781119941835. URL: http:

//books.google.com/books?id=QM60LmgaeeQC. High wind ride through: Intelligently providing more power

• utput. Siemens Energy. URL:

http://goo.gl/AmZxPr (visited on 09/01/2014).

Suryanarayanan ECE 566 Lecture/Week 2