ENGINEERING CHALLENGES FOR FUTURE WIND ENERGY DEVELOPMENT Neil D. Kelley

National Wind Technology Center

11th H.T. Person Homecoming Lecture in Engineering

University of Wyoming

October 13, 2006

October 13, 2006 N.Kelley --- H.T. Person Homecoming Lecture 2

We Will Be Discussing . . . • What has been accomplished in wind energy technology

to date?

• What are the future goals?

• What are current barriers to meeting those goals?

• What are the engineering challenges that will need to be surmounted in order to overcome these barriers?

• The need for a multi-disciplinary approach to carry out those challenges.

October 13, 2006 N.Kelley --- H.T. Person Homecoming Lecture 3

Where the Wind Is In the United States

October 13, 2006 N.Kelley --- H.T. Person Homecoming Lecture 4

What has been accomplished in wind energy technology to date?

October 13, 2006 N.Kelley --- H.T. Person Homecoming Lecture 5

October 13, 2006 N.Kelley --- H.T. Person Homecoming Lecture 6

There are a Range of Wind Turbine Sizes and Applications

Small (≤10 kW) • Homes (Grid connected) • Farms • Remote Applications (e.g. battery changing,

water pumping, telecom sites, icemaking)

Intermediate (10-500 kW) • Village Power • Hybrid Systems • Distributed Power

Large (500 kW – 6 MW) • Central Station Wind Farms • Distributed Power • Offshore Wind Generation Stations

October 13, 2006 N.Kelley --- H.T. Person Homecoming Lecture 7

Growth of Wind Energy Capacity Worldwide

010000200003000040000500006000070000

90 91 92 93 94 95 96 97 98 99 '00 '01 '02 '03 '04 '05 '06 '07 '08

Rest of World

Actual Projected

Rest of World

North America North America

Europe Europe

Jan 2006 Cumulative MW = 56,813

Rest of World = 7,270

North America = 9,550

Europe = 39,993

Sources: BTM Consult Aps, Sept 2005 Windpower Monthly, January 2006

October 13, 2006 N.Kelley --- H.T. Person Homecoming Lecture 8

2012 Goal : 3.6 cents/kWh with no PTC#

Cost of Energy Trend

1981: 40 cents/kWh

Decreasing Cost Due to: • Increased Turbine Size • R&D Advances • Manufacturing improvements

NSP 107 MW Lake Benton, MN wind farm

2006: 5-8 cents/kWh with no PTC# Cost Increases Due to: • Price increases in Steel & Copper • Turbines Sold Out for 2 Years

#Federal production tax credit

October 13, 2006 N.Kelley --- H.T. Person Homecoming Lecture 9

How has this been accomplished?

October 13, 2006 N.Kelley --- H.T. Person Homecoming Lecture 10

The Wind Turbine Designer’s Toolbox: The NWTC Suite of Advanced Numerical Simulation Codes

Measurements(power, loads, accel., wind)

Aerodynamics(AeroDyn)

StructuralDynamics

(FAST, ADAMS)

Controls(user-defined)

Wind Field(TurbSim, field

exp., etc.)

Actuator Inputs(blade pitch, gen. torque, yaw)

Aerodynamic Loads(lift, drag, pitch mom.)

Blade Motions(blade pitch, element pos. & vel.)

Wind-Inflow

Time Series Loads(forces, moments)

Time Series Motions(defl., vel., accel.)

OutputOther

ExternalConditions External Loads

(earthquake, wave)

Platform Motions(defl., vel., accel.)

October 13, 2006 N.Kelley --- H.T. Person Homecoming Lecture 11

The Development of New Testing Facilities

A new 45-meter wind turbine blade design being tested in the NWTC Blade Test Facility

Latest blades are now reaching 61.5 m lengths for 5 MW size turbines.

October 13, 2006 N.Kelley --- H.T. Person Homecoming Lecture 12

Tools for Developing Advanced Generators and Drive Trains

GEC NPS

Today 1.5 MW Commercial Technology

Tomorrow Prototype Technology

NWTC 2.5 MW Dynamometer Facility

October 13, 2006 N.Kelley --- H.T. Person Homecoming Lecture 13

Meet the Need for Understanding Available Materials and Developing New Ones

October 13, 2006 N.Kelley --- H.T. Person Homecoming Lecture 14

Future Goal: Provide 20% of U.S. Electrical Energy from Wind by the Year 2030

Increasing the reliability and service lifetime of wind turbine components and systems (risk reduction)

Improving both the power quality and consistency to increase the net worth of wind-generated electricity

Reducing the cost of wind turbine operations and maintenance

Removing technical barriers/issues

Achieve This Through Market Transformation by . . .

October 13, 2006 N.Kelley --- H.T. Person Homecoming Lecture 15

What Are the Barriers To Meeting These Goals? • Adequate transmission to connect wind resource regions

with load centers

• The current level of intermittency and the accuracy of wind forecasts

• The accuracy of the initial resource assessment and the lack of site-specific characteristics in those assessments that may affect the operation and lifetime of the installed turbines

• Interference with ground-based RADAR and other military and civilian communications and navigational systems

• Environmental impacts such as avian interactions, noise, esthetics

October 13, 2006 N.Kelley --- H.T. Person Homecoming Lecture 16

Advanced Wind Turbine Component Design Studies

WindPACT: Wind Partnership for Advanced Component Technologies

Blades

Drive Trains

Towers

October 13, 2006 N.Kelley --- H.T. Person Homecoming Lecture 17

Where is the Wind Resource Located That Will Provide the Needed Power to Feed the Primary U.S. Load Centers?

• Onshore

• Offshore

October 13, 2006 N.Kelley --- H.T. Person Homecoming Lecture 18

onshore and offshore

Source of Wind Energy for 20% Scenario

October 13, 2006 N.Kelley --- H.T. Person Homecoming Lecture 19

U.S. Rational to Pursue Offshore Wind Energy Development

US Population Concentration US Wind Resource

Graphic Credit: GE Energy

% of with Class 3 winds or above

• Windy onshore sites are not close to population centers • The electric utility grid cannot be easily set up for interstate transmission • Load centers are close to offshore sites

October 13, 2006 N.Kelley --- H.T. Person Homecoming Lecture 20

Region 0 - 30 30 - 60 60 - 900 > 900New England 10.3 43.5 130.6 0.0Mid-Atlantic 64.3 126.2 45.3 30.0Great Lakes 15.5 11.6 193.6 0.0California 0.0 0.3 47.8 168.0Pacific Northwest 0.0 1.6 100.4 68.2Total 90.1 183.2 517.7 266.2

GW by Depth (m)

U.S. Offshore Resource

Southeast and Gulf Coasts have not been evaluated

October 13, 2006 N.Kelley --- H.T. Person Homecoming Lecture 21

What Are The Engineering Challenges Necessary To Overcome These Barriers? • Develop engineering solutions and methodologies that utilize

new materials, structures, and controls to accommodate a wide range of turbine operating environments

• Understanding the detailed role of atmospheric motions in the aeroelastic response of wind turbine structures and its long-term consequences

• Collaborate with the atmospheric science community in the development of new tools to predict not only future wind farm power output over a period of 24-48 hours in advance but conditions that may have a deleterious impact on turbine operations

October 13, 2006 N.Kelley --- H.T. Person Homecoming Lecture 22

Coming to Grips with Turbulence Within the Atmospheric Boundary Layer and Its Impact on the Dynamic Response of Wind Turbines

• Wind turbines experience the greatest numbers of fatigue cycles of any man-made structure within their lifetime

• The source of these cycles is primarily atmospheric turbulence

October 13, 2006 N.Kelley --- H.T. Person Homecoming Lecture 23

Multi-Megawatt Capacity Wind Turbines Are Huge Structures

Boeing 747-400

GE 3.6 MW Turbine Designed for Offshore Use 104-m Rotor Diameter

October 13, 2006 N.Kelley --- H.T. Person Homecoming Lecture 24

A Ubiquitous Structure in the Nighttime Atmospheric Boundary Layer: The Low-Level Jet Stream

Eventual Max Turbine Depth

p

4 6 8 10 12 14 16 18 20 22

Hei

ght (

m)

0

100

200

300

400

500

Typical Vertical Wind Profiles Associated With Low-Level Jets

Lamar, Colorado

Low-Level Jet

10-min mean wind speed (m/s)

Strong Correlation Between Wind Resource and Jet Bi-annual Frequency

After Bonner, 1968

October 13, 2006 N.Kelley --- H.T. Person Homecoming Lecture 25

Source: R. Banta, NOAA/ESRL

Horizontal distance (km)

Hei

ght (

km)

waves low-level jet

organized turbulent air motions from waves

height of wind speed maximum

high vertical shear region

LIDAR Observation of Wave Motions in Southern Kansas

Low-Level Jets Are Responsible for the Generation of Organized or Coherent Turbulence by Atmospheric Wave Motions

SCHEMATIC OF COHERENT TURBULENCE GENERATION

October 13, 2006 N.Kelley --- H.T. Person Homecoming Lecture 26

LIDAR Observation of Low-Level Jet and Spatial Distribution of Turbulence in Southeast Colorado

20:16 to 21:12 LST 23:11 to 23:29 LST 15 September 2003

Jet Maxima

Organized Turbulent

Region Turbine Rotors

October 13, 2006 N.Kelley --- H.T. Person Homecoming Lecture 27

Role of Jets and Turbine Structural Loads Intense vertical shear and stable flow beneath the low-level jet provides the catalyst for developing atmospheric wave motions

Breaking atmospheric wave motions produce bursts of coherent turbulence

Transient loads are induced when turbine rotors encounter coherent turbulent regions

October 13, 2006 N.Kelley --- H.T. Person Homecoming Lecture 28

0

100

200

300

400

500

600

700

12 AM 4 AM 8 AM 12 PM 4 PM 8 PM 12 AM

Time

Faul

t Tim

e (h

ours

)

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

Win

d Sh

ear E

xpon

ent

Fault TimeShear

Diurnal Variation in Turbine Fault and Vertical Wind Shear Patterns Observed at Big Spring, Texas

Number of Hours With Turbines In Fault Status

Vertical Wind Shear

Source: Global Energy Concepts

Turbines Tend to Develop Fault Conditions More Often at Night. Why?

peak low-level jet activity

October 13, 2006 N.Kelley --- H.T. Person Homecoming Lecture 29

The Need for Close Collaboration Between the Engineering and Atmospheric Science Communities • Atmospheric dynamics clearly have a significant impact on

wind turbine operations and longevity beyond just the amount of wind energy available for power production

• It is likely that turbine load reduction will require a more detailed knowledge of turbulent atmospheric structures and mitigation approaches that include real-time atmospheric measurements in the control scheme

• The future ability to utilize operational weather forecast models to warn of potentially harmful events as well as predicting future power production will contribute to increased wind farm productivity and efficiency

October 13, 2006 N.Kelley --- H.T. Person Homecoming Lecture 30

An Example of Collaborative Synergism

Development of a Low-Dimensional Wind Turbine Inflow Model William Lindberg Jonathan Naughton Department of Mechanical Engineering Thomas Parish Robert Kelly Department of Atmospheric Science John Spitler Department of Mathematics

Simulated detailed turbine inflow

Low-dimensional reconstruction

October 13, 2006 N.Kelley --- H.T. Person Homecoming Lecture 31

The Engineering Challenge of Building Wind Farms Offshore

•Platforms

•The Operating Environment

October 13, 2006 N.Kelley --- H.T. Person Homecoming Lecture 32

The Development of Turbine Platforms for Deep Water Installations

Current Technology

October 13, 2006 N.Kelley --- H.T. Person Homecoming Lecture 33

The Deep Water Operating Environment: A Major Engineering Challenge Turbulent winds Irregular waves Gravity / inertia Aerodynamics:

induction skewed wake dynamic stall

Hydrodynamics: scattering radiation hydrostatics

Elasticity Mooring dynamics Control system Fully coupled

October 13, 2006 N.Kelley --- H.T. Person Homecoming Lecture 34

Conclusions

• A tremendous opportunity exists for engineers trained in a range of disciplines to contribute to the development of a mature wind energy industry poised to meet the 2030 goal.

• The same holds true for meteorologists who wish to work in numerical forecasting and those who enjoy problem solving and working with engineers toward a common goal.

• Future progress on overcoming the barriers discussed and improving the reliability and worth of wind-generated electricity will depend on the extent these problems are approached using a multi-disciplinary, synergistic methodology.