National Renewable Energy Laboratory (NREL) - Innovation for Our Energy Future
Up to Wind Speed

March 2012 Newsletter

Up to Wind Speed is a quarterly newsletter from the U.S. Department of Energy's National Wind Technology Center (NTWC) at the National Renewable Energy Laboratory (NREL).

For more than three decades, research conducted by NREL's Wind Program has helped industry advance wind energy technology, increasing reliability and lowering the cost of energy. Each quarter, the newsletter keeps you up to speed on what's happening in wind energy research and development and provides you with links to the NWTC's recent publications.

Articles in this issue:

Siemens/NREL Analyze Wind Turbine Data

A large multi-megawatt wind turbine and a meteorological tower are shown at the National Wind Technology Center against the backdrop of the Flatiron Mountains near Boulder, CO.

The Siemens 2.3 MW wind turbine and 135 m meteorological tower at the National Wind Technology Center. NREL PIX/20018.

A Siemens 2.3 MW wind turbine, with a 101 m blade diameter, installed at the National Wind Technology Center (NWTC) offers researchers the opportunity to explore many areas of wind energy technology including load response, structural characteristics, acoustic emission, aerodynamic performance, advanced measurement techniques, validation datasets, and improvement to design codes. A 135 m meteorological (met) tower upwind of the large turbine provides inflow data, which can be used to measure turbine energy output, structural and aerodynamic performance characterization, and aid in boundary layer atmospheric research. In addition, it enables the testing of remote sensing systems, such as SODAR and LIDAR.

During the 2011 wind season (approximately October 2010 through May 2011), initial data was collected from an advanced aerodynamics measurement system installed on the turbine and from the multiple instruments on the met tower.  An analysis of these data formed the basis for a joint paper between Siemens and NREL, presented at the AIAA Aerospace Sciences Meeting in January 2012, titled Inflow Characterization and Aerodynamics Measurements on a SWT-2.3-101 Wind TurbinePDF.

With the 2012 wind season underway at the NWTC, the Siemens research team is focused on recalibration of the aerodynamics system in the turbine. NREL researchers are focused on improving data quality from the 135 m meteorological tower and streamlining the data processing techniques used to validate the large volume of data coming from the tower's instruments.  The Siemens and NREL teams will compile data from the 2012 wind season to form a database that researchers working in many wind energy areas can draw upon for many years to come.

Researchers Simulate Atmospheric Turbulence and the Aerodynamics of Wind Plants

The figure perspective from above shows how wind blows through a wind turbine farm.

A view of the simulated wind plant from above showing contours of velocity normalized by the turbine hub-height has a mean wind speed of 8 m/s in a horizontal plane at the turbine hub height. The 48 2.3 MW turbines are shown as black lines. The wind is from the lower left blowing toward the upper right side of this domain, which is 4 km by 4 km in size. The low-speed turbulent wakes are clearly visible in blue.

Researchers at NREL have been performing large-eddy simulations (LES) of wind plant aerodynamics.  LES simulates important details of fluid flow and the turbulence.  It is an excellent tool for simulating turbulent winds and their interactions with wind turbines.  In the past year, NREL researchers have been among the first to study the effects of atmospheric turbulence and wind turbine wakes on turbine power production and mechanical loading, and to perform simulations of full, operational wind plants.

Wind plant aerodynamics are particularly complex. Each turbine creates a wake as a byproduct of energy extraction that extends far downwind of the turbine.  The air in the wakes contains less energy than the ambient wind and may contain stronger turbulence.  Hence, turbines within a wind plant that encounter other turbine wakes, i.e. they are downwind, produce less energy and  may be subject to more damaging aerodynamic loads than the turbines on the upwind side of the plant. To complicate matters, turbines and their wakes are heavily influenced by the state of the wind.  Every day the Earth's surface undergoes the natural heating and cooling cycles associated with the coming of day and night.  The wind responds to this cycle.  For example, during the day, the warm layer of air that forms near the surface feeds turbulent plumes that can then interact with turbines and their wakes.  During the night, the cooling of air near the surface acts to suppress turbulence and creates a strong vertical shear of wind speed and direction across the rotor of large turbines resulting in large amplitude cyclic loads on the turbine components. 

Such effects are not well understood, but NREL's wind plant aerodynamics simulations and research are helping to improve our understanding.  These simulations require the use of high-performance computers with thousands of processors, but the knowledge produced can be used to improve the simpler, faster tools used by industry to predict wind turbine mechanical loads and wind plant energy production.

Atmospheric and Wake Turbulence Impacts on Wind Turbine Fatigue LoadingPDF, a paper published by NREL researchers, highlights the important role that turbulent structures, like turbulent plumes in the atmospheric boundary layer, and wind turbine wakes play on both mechanical loading and power production.

NREL also performed the first LES of an entire operational wind plant, as opposed to simulating only a few rows of the plant, and published findings in the paper, A Large-Eddy Simulation of Wind Plant AerodynamicsPDF.  The simulated power production agrees well with the power production data from an actual wind farm, and the paper outlines a methodology for performing wind plant simulations. In addition, it sets the stage for further work in which atmospheric turbulence and wind speed and direction will be varied to better understand the wind plant response in terms of power production and loads.  Simulations also allow researchers to study the effects of novel control schemes to increase power production and decrease loads.

Lessons of Wind Energy Accelerate Water Power

The U.S. marine energy industry is actively pursuing development of offshore wind and MHK energy systems. Marine hydrokinetic (MHK) energy devices are high-force, low-speed machines, similar to wind turbines that convert the kinetic energy of a moving fluid into electrical energy. Production of energy through the Earth's largest, most predictable, and renewable water resources – its oceans and rivers – will require increasingly efficient, high capacity devices designed and deployed to maximize performance and reduce capital costs.

The NWTC's expertise to model, test, and validate device performance has been extended to water power devices and critical research efforts are underway to support this new industry. Experience in the wind energy sector demonstrates that these types of new technology developments require:

  • Modeling the important physics and validation of these models with test data
  • Rigorous testing of sub-scale and full-scale components and systems
  • Anticipating that prototype machines may fail and learning from the failures through comprehensive measurements during operation
  • Developing comprehensive international standards for design of these systems at an early stage of development
  • Performing studies at proposed prototype test sites to learn whether effects on the environment are significant.
Four types of kinetic energy conversion devices are shown: a horizontal axis turbine, a vertical axis turbine, an oscillating hydrofoil and a Venturi effect turbine.

Four typical kinetic energy conversion devices, as adapted from Bedard, resembling early wind turbines. Reprinted with permission. (Bedard, R. "Overview: EPRI Ocean Energy Program." Presented to the Duke University Global Change Center, (April 2006). Accessed May 2010.)

To support the development of the U.S. MHK industry under the Department of Energy's (DOE) Water Power Program, NWTC is leveraging its many years of experience in modeling and testing wind turbines and applying these lessoned learned to accelerate the development and deployment of water technologies. Existing wind turbine analysis codes for modeling wind turbines are being adapted and used to design more cost effective tidal and ocean current turbines. These analysis codes have been extensively verified and validated for the wind industry and are used by major U.S.-based wind turbine designers, manufacturers, consultants, and researchers. Their application to new MHK technologies will save time and money for water device manufacturers.

In addition, NWTC researchers are applying the lessons learned testing wind systems to MHK devices to assist the burgeoning water industry in verifying the structural integrity of blades, drive trains, and other components. Researchers are developing an instrumentation system tailored for testing wave and current components and full prototype systems, both in the laboratory and in open water environments. Again, the lessons from wind are being applied to ensure that the environmental inputs and device responses are accurately measured, so that the industry can verify performance and reliability, as well as track any problems to their root cause. This will ensure technically reliable machines prior to large scale deployments.

Wind industry experience is informing the early development of international guidelines for water device designs under the auspices of the International Electrotechnical Commission. DOE supports the development of these guidelines. The international standards guidance and experience of NWTC researchers, in partnership with industry and other national laboratories, ensures their relevance and sound technical basis. NWTC engineers and researchers contributed to the established baselines required to certify wind turbines and to standards that met the financial community's funding requirements.  Similar international standards will provide the MHK industry with a sound foundation for their evolving device development.

Collecting environmental response data is essential to show the impact of new technologies on the environment and wildlife. Siting and permitting lessons learned from wind industry experiences are being applied to water power to accelerate the testing of these new technologies in our oceans and estuaries.

These essential lessons learned by the wind industry reduce development time and costs to water device manufacturers, informing and supporting the development of innovative, reliable, and environmentally compatible devices using renewable water resources.

Energy Imbalance Market Offers Benefits to Western Interconnection

Renewable portfolio standards may increase installed wind capacity in the West to 50 GW by 2020, and significant quantities of solar generation are likely to be added as well. This increase in variable generation has raised concerns about how electric system operators will maintain balance between electricity production and demand in the Western Interconnection—especially in its smaller balancing areas. Meanwhile, uncertainties about future load growth and challenges of siting new transmission and generation resources may add additional stresses on the Western Interconnection in the future.

One proposed method of addressing these challenges is an energy imbalance market, in which balancing area authorities pool their variable and conventional generation resources to improve operational efficiency over a wider area. This sub-hourly, real-time energy market would provide centralized, automated, and region-wide generation dispatch for imbalances. By increasing the temporal and geographic footprint of the total balancing area, an energy imbalance market in the Western Interconnection could serve to moderate the variability of renewable generation resources and electricity demand. By introducing five-minute, security-constrained economic dispatch of generation resources to meet energy imbalances, the market also would introduce new efficiencies by enabling decision-making and response based on near-term system data. This could result in more efficient dispatch of generators, more efficient clearing of imbalances between demand and production, and a reduced need for flexibility reserves, which are often provided by quick-response generators, to address those imbalances.

NREL's Transmission and Grid Integration Group researchers are performing analysis on the flexibility reserve requirements of several forms of energy imbalance markets proposed in the Western Interconnection. In collaboration with the Western Electricity Coordinating Council, the group has examined the benefits of various implementation options. It is now incorporating more accurate data sets and using the Plexos model, which can simulate the five-minute dispatch of the energy imbalance market, to enhance its efforts. Results will be shared with utility commissioners and other stakeholders to inform future decision-making for Western Interconnection operations. In addition, the group works directly with a variety of balancing area authorities to identify individual benefits of energy imbalance markets for these groups.

For more information, see the group's first technical report, Flexibility Reserve Reductions From an Energy Imbalance Market with High Levels of Wind Energy in the Western InterconnectionPDF, and watch for additional reports this spring.

Large-scale Wind Turbine Blade Testing Facility Operational

A large turbine blade is being tested  in the large warehouse-like WTTC.

Clipper test article blade at the WTTC. NREL/PIX 20067

The Wind Technology Testing Center (WTTC), commissioned in the spring of 2011 in Boston, Massachusetts, provides world-class blade testing facilities. WTTC is the largest blade testing facility in the nation, using the most advanced test systems in the world. It has three test stands capable of testing wind turbine blades up to 90 m in length. It is operated as a partnership between DOE, NREL, and the Massachusetts Clean Energy Center (MassCEC).

As part of the design and certification process, wind turbine blade manufacturers must test full-scale blades to validate their structural design. Blade testing includes the simulation and testing of extreme one-time events, and demonstrable lifetime durability of the blade through multi-million cycle fatigue testing. WTTC provides the infrastructure and equipment needed to support these types of tests and validates the structural integrity of large-scale wind turbine blades. To verify the functionality of the facility and its test systems, WTTC partnered with Clipper Windpower to test one of Clipper's 2.5 MW turbine blades. The Clipper blade was subjected to static and fatigue load tests and WTTCs data acquisition systems were verified for data integrity. 

NREL worked closely with a large test system supplier, MTS Systems Corporation, to develop the novel large-scale test systems needed to apply loads and moments unique to wind turbine blades. The demand on these new test systems is tremendous. Blades for future 10 MW offshore wind machines must sustain test bending moments on the order of 80 million meters.

In addition to bending, the blade tip deflections of these large blades during maximum static loading approach 30 m. MTS supplied the NREL-developed Resonant Excitation technology that applies fatigue loads to the blades.  Hydraulic winches and actuators at the facility have force capacities of 100, 200, and 400 kilonewtons. NREL developed and supplied WTTCs advanced data acquisition system for customized blade testing. Hundreds of strain, force, and displacement measurements occur in a typical large blade test. NREL's data acquisition system is capable of measuring and recording hundreds of data channels at very fast sampling rates, while communicating with test control systems.

Since WTTCs commissioning test, several certification tests for industry partners have been completed. NREL has three staff members, with more than 30 years of blade testing experience, assigned to the WTTC facility. As NRELs Derek Berry, Supervisor of Engineering at the WTTC, explains, "This exciting new capability will enable pathways for accelerated wind deployment, and ensure that wind power is a cornerstone of the nation's energy infrastructure."

The development and operation of the facility is a result of a Cooperative Research and Development Agreement (CRADA) between MassCEC and NREL. At a total project cost of $38 million, more than a year of construction time was needed to complete the facility. Funding was provided by grants and loans from MassCEC, a $2 million dollar investment of capital equipment from NREL, and a $24 million investment of American Recovery and Reinvestment Act funds from DOE. For more information, contact Rahul Yarala, Executive Director—Wind Technology Testing Center, Massachusetts Clean Energy Center at 617-315-9307.

Wind Powering America Publishes Summary Report of Wind for Schools Project, Hosts Fifth Annual Wind for Schools Summit

People stand below a recently installed wind turbine.

Wind for Schools installation in Northumberland County, Virginia. Credit: Remy Luerssen Pangle. NREL PIX/18543.

To highlight the accomplishments of the successful 11 state initiative, Wind Powering America recently published Wind Powering America's Wind for Schools Project: Summary Report. The report provides an overview of the Wind for Schools project and details the activities and progress in all the Wind for Schools project states including descriptions of school installations, WAC activities, curricula and teacher training activities, funding updates, and contacts in each state. It also provides a comprehensive list of more than 80 host project installations since the program's inception.

Wind Powering America also hosted the fifth annual Wind for Schools Summit at the National Wind Technology Center on January 12 and 13, 2012. Close to 40 attendees shared their experiences from the past year, including developments in their individual programs and future plans. 
In 2008, the U.S. Department of Energy's Wind Powering America initiative launched the Wind for Schools project, which focuses on K-12 and university educators and students to promote workforce development and counter the trend of reduced numbers of U.S. students entering science and engineering fields. Wind for Schools project teams in 11 states work toward this goal by:

  • Developing Wind Application Centers (WACs) at universities. WAC students assist in implementing school wind turbines and participate in wind courses, preparing them for work in the wind or other power sectors. The WACs become centers of excellence to provide wind information across the state.
  • Installing small wind turbines at community "host" schools, introducing communities, teachers, students, and local utilities to wind technology to spur discussions and firsthand knowledge of wind energy technologies and address public resistance to wind energy deployment
  • Implementing teacher trainings with interactive curricula at each host school.

Wind Powering America initially funded six states (Colorado, Idaho, Kansas, Montana, Nebraska, and South Dakota). In fiscal year 2010, Wind Powering America funded five additional states (Alaska, Arizona, North Carolina, Pennsylvania, and Virginia) after a competitive request for proposals. The second round of funding began supporting projects in 2010 and is expected to last for approximately three years. The project has also initiated an affiliate program that allows schools or states outside of the DOE-funded group to participate.

Wind Powering America's 2011 Webinar Series

Wind Powering America is a nationwide initiative of the U.S. Department of Energy's Wind Program designed to educate, engage, and enable critical stakeholders to make informed decisions about how wind energy contributes to the U.S. electricity supply. As part of its education effort, Wind Powering America hosts a monthly series of free webinars on current wind energy issues. Audio visual files and text versions of each webinar are available after the event on the Wind Powering America website. The webinar archives include presentations from 2007 to 2012.

One of Wind Powering America's webinar series postcards.

December 2011: Wind and Wildlife Interactions

Presenters: Taber Allison, American Wind Wildlife Institute; Cris Hein, Bat Conservation International; Christy Johnson-Hughes, U.S. Fish and Wildlife Service

December 2011: Wind Power Economics: Past, Present, and Future Trends

Presenters: Mark Bolinger and Ryan Wiser, Lawrence Berkeley National Laboratory; Eric Lantz, National Renewable Energy Laboratory

November 2011: Wind for Schools Project Overview

Presenters: Karin Wadsack, Northern Arizona University; Dennis Scanlin, Appalachian State University; Michael Arquin, KidWind Project; Rebecca Lamb, National Energy Education Development Project

October 2011: Offshore Wind Development and Industry Update

Presenters: Christopher Hart, U.S. Department of Energy; Darryl Francois, Bureau of Ocean Energy Management

September 2011: Wind Powering America Program Update

Presenters: Ian Baring-Gould, Charles Newcomb, and Suzanne Tegen, National Renewable Energy Laboratory

August 2011: Jobs and Economic Development Impacts

Presenters: Suzanne Tegen and Eric Lantz, National Renewable Energy Laboratory; Peggy Beltrone, Exergy Integrated Systems

July 2011: Myths and Benefits of Wind Energy

Presenters: Ian Baring-Gould, National Renewable Energy Laboratory; Ed DeMeo; Ben Hoen, Lawrence Berkeley National Laboratory

June 2011: Community Wind Projects

Presenters: Stephanie Savage, NexGen Energy Partners; Tom Wind, Utility Wind Consulting; Mark Sinclair, Clean Energy States Alliance

May 2011: Transmission and Wind

Presenters: Jeff Hein, National Renewable Energy Laboratory; George Shultz, U.S. Department of Agriculture; Theresa Williams, Western Area Power Administration

April 2011: Wind Turbine/Radar Interactions

Presenters: Jose Zayas, Sandia National Laboratories; Dave Belote, U.S. Department of Defense; Ed Ciardi, National Oceanic and Atmospheric Administration

March 2011: Small and Distributed Wind

Presenters: Heather Rhoads-Weaver, eFormative Options; Mike Bergey, Bergey Windpower; Trudy Forsyth, National Renewable Energy Laboratory

February 2011: Cost of Wind Energy, Project Financing, and Funding

Presenters: Amy Hille, American Public Power Association; Mark Bolinger, Lawrence Berkeley National Laboratory; Brian Minish, South Dakota Wind Partners

January 2011: Workforce Development in Wind Technologies

Presenters: Michelle Seppala Gibbs and Doug Lindsey, Lakeshore Technical College; Giri Venkataramanan, University of Wisconsin; Ian Baring-Gould, National Renewable Energy Laboratory

Tribology Seminar Focuses on Improved Turbine Reliability

Example of micropitting on gear teeth.

NREL/PIX 19857

Surface damage and failures in contacting components (i.e., bearings, and gears) are among the more frequent and costly types of failures for a wind turbine and can be the root cause of system failure for the gearbox, main rotor bearing, generator, yaw system, and blade pitch systems.  Understanding and addressing the fundamental factors that influence contacting element performance was one of the main objectives of the 2011 Wind Turbine Tribology Seminar sponsored by the National Renewable Energy Laboratory (NREL), Argonne National Laboratory (ANL), and the U.S. Department of Energy. The seminar was held on November 15-17, 2011, at the Renaissance Boulder Flatiron Hotel in Broomfield, Colorado.

Tribology is the science and engineering of interacting surfaces in relative motion. The seminar covered fundamental tribological topics most relevant to wind applications that lead to early wind turbine failure and system down time. These included elastohydrodynamic lubrication behavior and surface interaction, and lubricant fundamentals including formulation, synthetics, and greases.

Seminar participants concluded that lubricants used in wind turbine applications are subjected to extreme environmental and operational conditions and are expected to maintain their performance throughout operation. Therefore, they require higher standards than similar lubricants for other industries.  Synthetic lubricants typically offer better cost benefit throughout the life cycle.  Development of new lubricants typically involves a systemic approach of blending different concentrations of certain additives to balance various performance characteristics including scuffing, micropitting, wear, oxidation stability, compatibility with elastomers and paints, foaming, and other phenomena.  In addition to gear oil lubricants, greases are used in many bearing components, such as the generator, main shaft, pitch, and yaw bearings; each has its own design requirements.

The Wind Turbine Tribology Seminar (1) presented tribology fundamentals, lubricant formulation, selection of oils and greases, gear and bearing failure modes, R&D into advanced lubricants, and mathematical modeling for tribology, and field observations; (2) provided a forum for researchers, tribologists, lubricant engineers, wind turbine manufacturers, gearbox manufacturers, bearing manufacturers, owners, operators, and those in the supply chain to share their knowledge and learn from their colleagues; and (3) developed an R&D roadmap to guide future wind turbine tribology research. The seminar consisted of six sessions with 29 moderators, speakers, and panelists and 110 people attended the seminar and participated in the discussions.

Held November 15-17, the seminar identified the major tribological related issues affecting the wind energy industry and coordinated recommendations for future research and development strategies that the U.S. Department of Energy (DOE) and other organizations can use to focus their efforts to improve turbine reliability and, ultimately, lower the cost of wind energy.

Recent NWTC Publications — November 2011-January 2012


Pie charts shows breakdown of the types of wind publications NREL published from November through January.

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