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

March Newsletter

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

For more than two decades, research conducted by NREL's Wind Program has helped industry advance wind energy technology, increasing reliability and lowering the cost of energy. As we continue our efforts with the wind industry in 2011, we will keep you up to speed on what's happening in wind energy research and development and provide you with links to NWTC's recent publications.

In this issue:

Wind Energy Systems Engineering Workshop

NREL hosted a wind energy systems engineering workshop on December 14, 2010, at the National Wind Technology Center (NWTC) that included a range of invited speakers from academia, industry, and international research laboratories.

Systems engineering represents a holistic approach to design, where significant engineering components and life-cycle costs of the product are modeled in the design process. Systems engineering approaches are used routinely outside of the wind industry, in industries such as aerospace, and can result in significant performance improvements and savings in capital and operating costs. In spite of the fact that many levels of wind energy design are closely coupled, from individual components to long-term system operational plans, a framework that spans the range of scales for wind plant design does not exist.

NREL's workshop sought to fill this gap by outlining the requirements for a systems engineering approach in wind plant design through the development of an open and flexible systems engineering framework that can be used for the multidisciplinary analysis and design of complete wind energy plants. Workshop participants then discussed feasible methods for implementing a tool to accomplish this.

The workshop participants agreed on a framework that will: 1) provide governmental agencies (e.g. DOE) with a validated tool to evaluate the impact of new technologies on overall cost of energy and deployment scenarios, and 2) provide the wind industry with a systems engineering design tool that can be used to design, optimize, and operate future wind plants more effectively across the diverse stakeholder groups.

A white paper describing the development of a comprehensive tool will be drafted for public comment in the coming months. The paper will also examine current tools and capabilities, as well as cost modeling capabilities and gaps. View the workshop presentations.

Astronomical Alstom

Installation of the Alstom Turbine at the  NWTC. PIX 18496.

The 2010-2011 winter testing season at the NWTC has begun with all eyes focused on the installation of a 3-MW Alstom Eco100.

Using a crane that can lift 1,350 tons, the first three sections of Alstom's 90-m tower went up one at a time. Then, the two uppermost sections of the tower, the nacelle, and the blades were lifted into place and attached on the same day.

When one of the three 160-foot-long blades of the turbine reaches straight into the sky, the entire structure reaches 140 m (460 ft) above the ground and is the tallest wind turbine at the NWTC.

The turbine, including the tower,  weighs just under 500 tons, with each blade weighing about 11 tons and the 10-meter by five-meter nacelle weighing 95 tons. At its base, the 90-meter tower is about 4.5 m (14 ft) in diameter. To ensure that it withstands the winter winds blowing at the site, the tower's foundation required 70 truckloads of concrete.

The Alstom Eco 100 will undergo a series of certification tests: a power quality test to finalize the IEC requirements for Type Certification of the 60 Hz unit and additional complimentary measurements of power performance, acoustic noise, and system frequency measurements that are standard Alstom practice. Later, the turbine will undergo drive train modeling tests and validation.

Meanwhile, Alstom is also building its first North American assembly facility, a 115,000 square foot wind power turbine assembly facility in Amarillo, Texas, creating U.S. jobs and spurring its wind turbine production for the U.S. market. Alstom's North American Wind Business is headquartered in Richmond, Virginia. Globally, Alstom currently has 87 MW of ECO 100 units in operation since 2008, with more than 136,000 operating hours and an additional 231 MW under construction.

Measuring the Wind

Technicians ascending cables to work on the 440 foot meteorological tower at the NWTC. PIX 18493.

Technicians from Rhodes Tower Services installing one of the 1500 pound booms on the 440 foot meteorological tower at the National Wind Technology Center. PIX 18494.

Stretching into the Colorado sky more than 440 vertical feet tall, two new meteorological towers now grace the National Wind Technology Center (NWTC).

Lit with LED lighting required by the FAA, and spaced 735 meters apart, these unique towers will help researchers evaluate boundary layer winds and coherent turbulence and characterize the inflow to the multimegawatt research turbines downwind.

Typically, meteorological towers have been built to wind turbine hub height. Because the new towers reach heights at the tops of the rotors of the multimegawatt turbines at the wind site, they measure the entire sweep of inflow to the rotors. Instrumented towers help to measure the wind that determines the adjacent wind turbine rotor response to the wind, the turbine's response to the rotor, and the foundation's response to the turbine.

Two vertical arrays of instruments are installed on each tower. One array has a set of traditional instruments that includes two dimensional anemometer cups, weather vanes, and thermometers. The set of instruments on the other array consists of three dimensional sonic anemometers to measure loads and turbulence. The sonic anemometers measure a 10-Hz wider bandwidth than traditional anemometers.

Ultimately, data collected from the meteorological towers will be accessible to industry partners, and other researchers, providing data to design better codes to build more reliable turbines that produce more power at lower cost.

Advancing Controls Research

Technicians ascending cables to work on the 440 foot meteorological tower at the NWTC. PIX 18493.

The challenge facing today's wind turbine designers is to capture the maximum amount of energy, with minimal structural loading, for minimal cost.

Researchers at the NWTC are studying conventional turbine component controls such as blade pitching, new components such as twist-coupled blades, and advanced devices such as micro-tabs to develop innovative rotor control strategies that mitigate unwanted aerodynamic loads at the rotor hub.

Loads cause damage that increases maintenance costs and can shorten the life of a turbine.

Design of control algorithms for wind turbines must account for multiple control objectives that are complex and nonlinear in dynamic systems driven by aerodynamic, gravitational, inertial, centrifugal, and gyroscopic loads. Thus, multimegawatt turbines require active control and damping systems that mitigate fatigue loads, maintain stability, and allow maximum energy capture.

Testing new control schemes is a critical step before new control systems can be implemented in commercial machines. Test facilities at the NWTC include two controls advanced research turbines (CARTs); the 3-bladed CART3 and the two-bladed CART2. Both turbines are used to field-test advanced control systems and related technologies.

By the end of 2010, the CART3 began operating in both variable-speed and constant-speed modes up to rated power. It will be used in the coming months to test advanced control systems. One of the first controllers tested will be an independent pitch controller developed at Garrad Hassan. A state-space controller developed at the NWTC also will be tested on the CART3 in the near term.

Projects utilizing the CART2 are ongoing as well. Currently, field-test data on the state-space control system is being collected. Results of this study, Refinements and Tests of an Advanced Controller to Mitigate Fatigue Loads in the Controls Advanced Research Turbine: Preprint, were presented at the AIAA conference in Orlando, January 2011.

Feed-forward control systems represent another area of research being pursued. Along with partners at the University of Colorado and the Colorado School of Mines, NWTC is developing control systems that utilize wind speed information gathered from light detection and ranging systems (LIDARS). System testing will occur on both the CART2 and the CART3. A Catch the Wind "Vindicator" LIDAR was installed on the CART3 and data collected from it is currently being compared to other measurements of wind speed. The CART2 is expected to have a LIDAR installed on it in the future. Results from these tests on the CART turbines will detail the potential benefits of LIDAR information in turbine control systems. The advantage of the LIDAR systems is that they sense the wind speed before it reaches the turbine.

In addition, an investigation of techniques for reducing the amount of blade noise emitted by the wind turbines is ongoing on the CART2.

An ongoing collaboration with CENER is using the CART2 to establish methods for closed-loop system identification for wind turbines. System-identification may benefit industry by allowing increased model accuracy for a specific turbine.

Finally, along with members of the grid integration group at the NWTC, a project is being undertaken to investigate the ability of wind turbines to provide active frequency control capabilities. These could include inertial response, governor response, and automatic generation control. Initial work will investigate possible controllers through simulation and potentially will involve field-testing of simulation-tested control systems.

2.2-MW Direct-Drive Power Train Testing at the NWTC 2.5 MW Dynamometer

Dynamometer drive train testing facility at NWTC.

Northern Power Systems (NPS) of Barre, Vermont is collaborating with NWTC engineers to test a prototype 2.2-MW direct-drive turbine at the NWTC's 2.5-MW dynamometer facility. Testing of the system began early in October 2010 and is expected to continue through February 2011. The NWTC dynamometer facility's unique capabilities are allowing NPS to conduct a variety of valuable tests over a short period of time. The facility also allowed NPS to bring all of the critical elements of their turbine for testing, including all up-tower components, except those replaced by the dynamometer — the hub and blades.  The comprehensive test plan enables NPS to reduce field deployment risks and accelerate commercialization.  Further testing will focus primarily on power train characterization and controls tuning.

The installation and commissioning of the NPS test article in the dynamometer presented a number of challenges and provided valuable design input for NREL's planned 5-MW test facility. The test article could not be assembled inside the dynamometer facility because of the 50-ton limit on the facility crane. Instead, the generator and tower top main frame were attached to a rolling test fixture outside using 400-ton and 100-ton mobile cranes. Once assembled, the power train was rolled into precise alignment with the dynamometer and bolted to the floor.

The 1.5-MW technology demonstrator that was the basis for the NPS generator now under test was originally developed and tested under NREL's Wind Partnerships for Advanced Component Technologies (WindPACT) and Low Wind Speed Technology (LWST) programs.  Testing the 2.2-MW turbine at the NREL dynamometer represents another productive partnership between NREL and NPS. 

Assessing Offshore Wind Power

NWTC researchers recently released the report, "Large-Scale Offshore Wind Power in the United States: Assessment of Opportunities and Barriers." The report includes a detailed assessment of the Nation's offshore wind resources and offshore wind industry, including future job growth potential. The report also analyzes the technological challenges, economics, permitting procedures, and the potential risks and benefits of offshore wind power deployment in U.S. waters.

The United States' offshore wind energy resources can significantly increase the wind industry's contribution to the nation's clean energy portfolio. The report finds that harnessing even a fraction of the nation's potential offshore wind resource, estimated to be more than 4,000 gigawatts, could create thousands of jobs and help revitalize America's manufacturing sector, reduce greenhouse gas emissions, diversify U.S. energy supplies, and provide cost-competitive electricity to key coastal regions. The report also concluded that while significant challenges remain, effective research, policies, and market commitment will enable offshore wind to play a significant role in the country's energy future.

The United States possesses large and accessible offshore wind energy resources. Wind speeds tend to increase significantly with distance from land, so offshore wind resources can generate more electricity than wind resources at adjacent land-based sites. The availability of these high offshore winds close to major U.S. load centers, i.e., coastal cities, significantly reduces power transmission issues.

The report estimates that U.S. offshore winds have a gross potential generating capacity four times greater than the nation's present electric capacity. While this estimate does not consider siting constraints and stakeholder inputs, it clearly indicates that the U.S. offshore wind capacity is not limited in resource magnitude. Uncertain regulatory and permitting requirements in federal waters (outside the three-nautical-mile state boundary) have posed major hurdles to development, but recent progress is clarifying these rules. Most notably, after nine years in the permitting process, the Cape Wind project off of Massachusetts was offered the first commercial lease by the Department of Interior in April 2010.

The United States has no offshore wind generating capacity to date. About 20 offshore projects representing more than 2,000 MW of capacity are in the planning and permitting process. Most of these activities are in the Northeast and Mid-Atlantic regions, and projects are being considered along the Great Lakes, the Gulf of Mexico, and the Pacific Coast.

Oahu Wind Integration and Transmission Study: Summary Report

NREL's Wind Systems Integration team led the Oahu Wind Integration and Transmission Study (OWITS) to examine grid and transmission integration of renewables as part of the Hawaii Clean Energy Initiative's Energy Agreement. The Hawaii Clean Energy Initiative includes an aggressive mandate for the state of Hawaii to generate 40% of its energy from renewable resources by 2030. The Energy Agreement includes a commitment to integrate up to 400 megawatts (MW) of wind energy from Molokai or Lanai and transmit it to Oahu via undersea cable systems (the "Big Wind" projects). The Big Wind element is a significant part of the 40% renewable energy goal. OWITS was composed of several small studies sponsored by the Hawaiian Electric Company, the state of Hawaii Department of Business, Economic Development, and Tourism (DBEDT), and the U.S. Department of Energy (DOE).

Map of Oahu, Molokai, and Lanai showing electricity potential from wind and photovoltaic generation.

Wind integration studies (e.g., the Eastern Wind Integration and Transmission Study and the Western Wind and Solar integration Study) performed over the last several years have examined the technical and operational aspects of integrating large amounts of wind and solar power into the bulk electrical grids. The methodologies and lessons learned from these studies were applied to an analysis of the island of Oahu grid.

OWITS is noteworthy because it is an important application of integrating wind power onto a smaller electrical grid system than other grid integration studies have typically encountered. In addition, the undersea cable is state-of-the-art technology and really pushes the envelope of undersea island-grid interconnection. Such technology and attaining a better understanding of its capabilities should prove quite helpful for domestic offshore wind development.

Grid Integration Workshops Galore

The following workshops and conferences provide a glimpse into the fast pace at which the power industry and technical analysis of variable-generation grid integration is moving these days. The depth of operational understanding is advancing dramatically with every passing year.

International Energy Agency Wind Task on Wind Integration/October 11-12, 2010

Michael Milligan (NREL) and Charlie Smith (UWIG) gave a presentation at the International Energy Agency (IEA) Wind Task 25 (Design and Operation of Power Systems with Large Amounts of Wind Power) Meeting, October 11-12, Montreal, Canada, titled U.S. Status: North American Electric Reliability Corporation (NERC) Task Force on Integrating Variable Generation (IVGTF). These IEA gatherings provide a crucial venue for sharing the very latest in research results and analytic methodologies with international subject experts.

UWIG Fall Technical Workshop/October 13-15, 2010

As an excellent, renowned, and highly credible organization and forum, UWIG and their technical workshops are hard to beat for the subject matter tackled. This workshop, attended by Michael Milligan, Brian Parsons, and Kirsten Orwig, members of the NREL Transmission and Grid Integration Group, provided attendees with an expanded perspective on the status of wind on utility systems in the United States, Canada, and other countries. This event was held in co-location with the 9th International Workshop on Large-Scale Integration of Wind Power into Power Systems as well as on Transmission Networks for Offshore Wind Farms (see below).

Workshop topics included:

  • Wind Plant Modeling and Power System Operations Developments;
  • Wind Integration Study Results and Market Design;
  • Wind Integration on Island Power Systems;
  • Fossil Fleet Flexibility Improvement;
  • Developments in Transmission;
  • IEA Wind Task on Wind Integration.

Michael Milligan presented Capacity Value: Results from the International Energy Agency Task 25 Collaboration.

9th International Workshop on Large-Scale Integration of Wind Power into Power Systems as well as on Transmission Networks for Offshore Wind Farms/October 18-19, 2010

Conveniently piggy-backed on to the earlier UWIG workshop, this workshop, considered one of the premier conferences in its field, provided an excellent platform for exchanging knowledge and ideas and sharing experiences around wind energy during two days. It was accompanied by the Fourth Workshop on Best Practice in the Use of Short-term Forecasting of Wind Power on October 16, 2010.

The following papers were presented by NREL staff and other co-authors:

Workshop on Active Power Control from Wind Turbines/January 27, 2011

This workshop, held in Boulder, CO, discussed the research needs and state of the art of providing active power control from wind turbines and wind plants. In general, the scope of the workshop included active power control in all forms, but in particular, the workshop focused on the areas of inertial response, primary control (frequency response), and secondary control (automatic generation control/AGC regulation). The workshop included about 40 participants from utilities, Independent System Operators (ISOs), manufacturers, universities, and other institutions. NREL and EPRI are pursuing a project in this area as are many universities, utilities/ISOs, and manufacturers. This workshop was aimed at guiding that research. Proceedings from this workshop will be available soon at on the Systems Integration Web site.

WPA Hosts Fourth Annual Wind for Schools Summit: A Wind Powering America Success Story

On January 6 and 7, Wind Powering America (WPA) hosted its fourth annual Wind for Schools Summit at the NWTC.

Established in 2005 to raise awareness in rural America about the benefits of wind energy, a significant goal for WFS is the development of a wind energy workforce. The Wind for Schools project currently is funded and supported by the U.S. Department of Energy (DOE) in 11 states (Alaska, Arizona, Colorado, Idaho, Kansas, Montana, North Carolina, Nebraska, Pennsylvania, South Dakota, and Virginia).

The 2-day event gave attendees a chance to share their experiences in funding, curriculum, and other developments that occurred during the past year.

More than 50 attendees met and discussed ways to further the Wind for Schools project in their states. Wind for Schools project manager, Larry Flowers, described the event as important to further Wind for Schools growth. Flowers explained, "It develops a network and a community where people feel comfortable calling each other up or sending e-mails saying, 'I'm stuck on this.' This way, the network develops into a vital experience where people can share and counsel. That's the purpose of this summit," Flowers said.

The summit gave representatives from five states recently established as Wind for Schools participants the opportunity to intermingle with representatives from established programs. Attendees learned from expert moderators about the different aspects of wind energy and the Wind for Schools project, including environmental and siting challenges, new curricula for the classroom, the role of rural and agricultural organizations, and small wind and installer certification.

Montana State University Wind Applications Center Director Robb Larson believes the summit allows participants to communicate on a level where everyone can learn from each other. "All participants, whether veteran or rookie, benefit by sharing experiences. The new states should be able to cherry-pick the best of these ideas and maybe avoid pitfalls encountered by the first participants, and we veterans come away with some new ideas," Larson said.

The annual meeting, which Flowers compared to the tradition of a spring powwow, also allows the team to look for ways that WPA can improve the overall Wind for Schools project.

As a result of Wind for Schools, hundreds of university students have experience in wind energy topics and perhaps thousands of K-12 students are aware of wind energy.

More information on the Wind for Schools project.

Recent NWTC Publications

All NREL publications are available at: NREL Publications Database

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