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

June Newsletter

Up to Wind Speed is a quarterly newsletter from NREL's National Wind Technology Center (NWTC).

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:

Alstom 3-MW Turbine Commissioned at NWTC

With a clip of the ribbon, an Alstom 3-MW Eco 100 wind turbine officially began its sojourn at the National Renewable Energy Laboratory's (NREL) National Wind Technology Center (NWTC) on April 26, 2011.

Andy Geissbuehler, vice president and general manager of Alstom, addresses participants at the commissioning ceremony for the 3-MW Eco 100 that soars into the sky behind him at the NWTC.

Andy Geissbuehler, vice president and general manager of Alstom addresses participants at the commissioning ceremony for the 3-MW Eco 100 that soars into the sky behind him at the NWTC.
PIX #18877.

"This is a very exciting day for all of us at Alstom, and we are delighted to share the celebration with our deeply valued partners from NREL," said Andy Geissbuehler, vice president and general manager of Alstom's wind business in North America. "Today's landmark event in the course of our ECO 100 – NREL partnership follows just a few short weeks after Alstom's first North American wind farms entered commercial operation. With the achievement of these two significant milestones, 2011 already is shaping up to be an exciting year for Alstom in this challenging and important market."

Participants at the ceremony included representatives from Alstom, Texas Tech University, The Amarillo Development Corporation, American Wind Energy Association, Garrad Hassan, Michels Wind Energy, Texas Tech University, RES Americas, Sandia National Laboratories, along with other representatives from NREL, industry, and the media.

NREL's National Wind Technology Center has the most extensive wind-turbine testing facility in the nation. Its researchers were excited to sign a cooperative research and development agreement with Alstom last May. Center Director, Fort Felker said, "Alstom's use of the NWTC to test its turbine provides them with the most experienced engineers and extensive wind turbine testing facility in the nation."

The 3-MW Alstom Eco 100 wind turbine 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 systemfrequency measurements that are standard Alstom practice.

NREL Participates in WINDPOWER 2011

Logo for AWEA 2010

More than twenty researchers and staff from NREL chaired and participated in meetings and met with industry attendees at the Windpower 2011 Conference and Exhibition in Anaheim, CA, on May 22-25.

Wind issues, technology, and policy addressed by NREL participants included:

  • Permitting Guidelines
  • Operations & Maintenance
  • Research & Development
  • Offshore Wind
  • Distributed Wind
  • Standards Development
  • Power System Operations

Topics of papers presented by NREL authors included:

  • Investigation of Data Fusion for Health Monitoring of Wind Turbine Drivetrain Components
  • Value of Balancing Cooperation and Wind Forecasting Improvements
  • How Does Wind Affect Cost? Cycling and Costs
  • Field Testing Active Power Control in Wind Turbines
  • Development in Cost Allocation for New Transmission

These papers are available in the NREL publications database at

WWSIS Phase 2 Kick-off: Focus on Thermal Cycling

WWSIS Phase 1
Phase 1 sought to answer the question: "Can we integrate 35% wind and solar in the West? The goal was to assess the operating impacts and economics of wind and solar on the WestConnect (a large group of utilities in the West) grid. Phase 1 found that it is feasible for WestConnect to accommodate 30% wind and 5% solar, if a handful of operation measures were implemented.

On March 16, 2011, the NWTC hosted the kick-off meeting for Phase 2 of the Western Wind and Solar Integration Study (WWSIS). This meeting formalized the creation of a Technical Review Committee, which includes individuals that collectively provide expertise in all of the technical disciplines relevant to the study. The goal of WWSIS Phase 2 is to examine, in greater detail and with higher fidelity, the impacts of wind and solar on thermal generation and potential mitigation options. Specifically, Phase 2 looks at impacts of cycling and ramping (i.e., increasing or decreasing plant or fleet power output to counter wind power variation) the thermal power generation units within the study region. The Committee decided to use PLEXOS (see article in this issue on this new modeling capability) for Phase 2 because it has the capability to optimize cycling/ramping costs/constraints and the ability to model sub-hourly.

As a necessary facet of this analysis, Phase 2 will need to assess generator cycling capabilities and minimum turndowns — some conventional power plants, often older ones, have limited turndown capabilities, making them less flexible. Compared to conventional thermal generation, hydropower generation is capable of quick start/stop cycling and fast ramping, which makes it a good partner for variable wind and solar generation. In addition, this characteristic makes hydropower a sensible candidate for mitigation of variability impacts on the grid, but other mitigation solutions also will be developed and analyzed in Phase 2.

Grid accommodation of variable generation, such as wind and solar power, will be greatly enhanced and improved from an operational standpoint when more flexible conventional thermal power plants (e.g., coal and gas) are available for ramping output up or down. Increased operation and maintenance costs (i.e., wear and tear) on conventional generators due to increased ramping and cycling, as well as issues pertaining to emissions impacts of cycling and ramping are all crucial areas of new analysis in WWSIS Phase 2. The issue is to what extent the present fleet of conventional power sources can provide flexibility and ramping, and at what economic and emissions costs.

WWSIS Phase 2 will:

  1. Obtain better data for wear and tear costs of thermal units during cycling and ramping
  2. Examine emission impacts of thermal generation cycling and ramping in greater detail
  3. Optimize unit commitment and economic dispatch with these inputs and examine impact of increasing penetrations of wind and solar on thermal units
  4. Examine mitigation options to reduce costs of thermal unit cycling and ramping.

Sub-hourly Grid Modeling Capabilities with PLEXOS

NREL plans to use PLEXOS in the Western Wind and Solar Integration Study – Phase 2 to examine the impacts of variable generation on conventional units, and in the Eastern Wind Integration and Transmission Study – Phase 2 to examine the ability of demand response to help integrate variable generation.

Traditional production cost modeling uses hourly time steps; however, many of the effects of renewable generation are apparent at the sub-hourly level. In the second phase of the integration studies, NREL researchers and analysts will refine the level of analysis, with sub-hourly grid modeling tools such as PLEXOS.

A schematic of the sub-hourly model. The model compares unit commitment to economic dispatch. In this example, 35 minutes of unit commitment between 10:00 and 10:35 translates to 35 minutes of economic dispatch.

Figure 1: A simple schematic that demonstrates the timing of unit commitment and economic dispatch decisions in a sub-hourly model.

PLEXOS is a next-generation, optimization-based simulation solution that uses linear programming capabilities. It is used by industry analysts and power companies to resolve regional reserve allocations, resource expansions, emission values, and market prices for energy and reserves.

The PLEXOS software models a 5-minute real-time energy and ancillary-service market dispatch, for areas as large and complex as the Eastern Interconnect, at a nodal level. It can be used to analyze the impact of variable generation on economic dispatch and the impact of variable generation on reserves. It offers more detailed modeling of conventional generator emissions that are the result of ramping events. It allows the analysts to examine the benefits of faster markets, balancing area cooperation, and shorter time horizon forecasting techniques.

NREL's Transmission and Grid Integration Group is comprised of experts on power grid integration of renewable power sources such as wind, photovoltaics, and concentrating solar power. With the use of new tools like PLEXOS, NREL can analyze unit scheduling at sub-hourly levels to utilize the most recently available information on variable output and the demand response to variable energy generation.

Report Studies Wind Energy Costs in 7 Countries

Cover of IEA Wind Task 26 report, titled "IEA Wind Task 26: Multi-national Case Study of the Financial Cost of Wind Energy."

An IEA report recently published by NREL finds that wind energy costs vary significantly among the countries studied.  The IEA Wind Task 26 — Multi-national Case Study of the Financial Cost of Wind Energy; Work Package 1 Final ReportPDF uses a multi-national case-study approach to understand the sources of wind energy cost differences among the seven participating countries.

This analysis considered the levelized cost of energy (LCOE) as the primary metric for describing and comparing wind energy costs from country to country.

The LCOE represents the sum of all costs over the lifetime of a given wind project, discounted to present time, and levelized based on annual energy production. The LCOE does not include any residual costs or benefits incurred beyond the project's assumed operational life. The LCOE comprises a number of components including the investment cost, operation and maintenance costs, financing costs, and annual energy production. Accurate representation of these cost streams is critical in estimating a wind plant's cost of energy. Some of these cost streams will vary over the life of a given project. From the outset of project development, investors in wind energy have relatively certain knowledge of the plant's lifetime cost of wind energy. This is because a wind energy project's installed costs and mean wind speed are known early on, and wind generation generally has low variable operation and maintenance costs, zero fuel cost, and no carbon emissions cost. Despite these inherent characteristics, there are wide variations in the cost of wind energy internationally.

Table depicts LCOE by Pounds per MWh and Dollars per MWh for Switzerland – 120 and 167; Netherlands – 94 and 131; Germany – 85 and 118; Spain – 83 and 115; Sweden – 67 and 93; United States – 65 and 91; and Denmark – 61 and 85.

The study focuses on land-based wind energy because of the availability of data though small samples of reported offshore cost data also are included. Seven countries participated in the study, including Denmark, Germany, the Netherlands, Spain, Sweden, Switzerland, and the United States.

Results of the analysis indicate that the unsubsidized LCOE varies considerably among countries represented in this study. As shown in the LCOE table above, the country-specific LCOEs range from €61/MWh ($85/MWh) in Denmark to €120/MWh ($167/MWh) in Switzerland.

Reliable Wind Turbine Drivetrains

Condition Monitoring to Lower Wind Energy Costs
This September, the Gearbox Reliability Collaborative (GRC) will present the findings of its Condition Monitoring Round Robin project at the Wind Turbine Condition Monitoring Workshop. All GRC participants will be invited to present their methods and results at the upcoming workshop, scheduled for September 19-21, 2011.  The main purposes of the workshop are to review current structural health and condition monitoring practices adopted by the wind industry, explore the state-of-art for structural health and condition monitoring for wind turbines, identify main research and development needs, learn from other industries with mature condition monitoring experiences, and investigate ways to make the monitoring techniques cost effective for the wind industry.

Condition Monitoring (CM)(1) techniques are widely used in many industries, such as the aircraft, nuclear power plants, and gas turbines.  Condition monitoring enables operators to evaluate component or system health and conduct condition-based maintenance rather than time interval-based maintenance, which can significantly reduce operation and maintenance (O&M) costs. Because O&M costs are one factor that the wind industry can address to reduce the cost of wind energy (COE), especially when turbines are installed offshore, there is a tremendous interest in applying CM techniques to wind turbine drivetrains.

The GRC's CM research integrates stress wave, vibration, lubricant, and electric signature monitoring techniques. The GRC completed initial tests on a generic gearbox at NREL's National Wind Technology Center's 2.5-MW dynamometer and preliminary test results are discussed in Investigation of Various Wind Turbine Drivetrain Condition Monitoring TechniquesPDF. The test results clearly reveal that a comprehensive approach to conducting wind turbine drivetrain CM is needed as no single technique provides solutions for all gearbox failures.

The GRC launched a Condition Monitoring Round Robin project in 2010 to evaluate various data analysis algorithms used in vibration-based wind turbine drivetrain condition monitoring. The project is unique in that all participants will not know the failure modes that were present in the test gearbox until results from all partners are submitted to NREL. As of April 2011, nineteen partners (12 from industry and 7 from universities) from the United States, Europe, and Australia were participating in the Round Robin. NREL provided data to the participants and they contributed data analysis expertise, which will facilitate the evaluation of different vibration algorithms and help establish baseline responses for drivetrain CM systems.

For further information on the Gearbox Condition Monitoring Round Robin, or the workshop, contact Shuangwen (Shawn) Sheng (, 303-384-7106) at the National Wind Technology Center.

CM can potentially alleviate premature component failures by: 1) detecting incipient failures early, thereby reducing the chances of catastrophic failures; 2) evaluating the health condition of components, which has the potential to enable more cost-effective O&M; and 3) analyzing root causes, which may provide inputs for improved turbine operation, control strategy, and component design. In the long-term, the correlation of CM outputs, combined with turbine operational conditions (e.g., rpm and power) and/or dynamic measurements (e.g., strain and displacement) of drivetrain components, will help to identify possible causes of component failures and strategies for improvement.

From a CM perspective of utility-scale wind turbine drivetrains, three major components—the main bearing, the gearbox, and the generator—comprise the system (Figure 1). Of these three components, the gearbox is the most costly to maintain through a turbine's 20-year design life and its replacement causes the longest downtime.(2, 3)  The National Renewable Energy Laboratory (NREL) initiated the Gearbox Reliability Collaborative (GRC) to determine the causes for premature gearbox failures and subsequently recommend improvements to gearbox design, manufacture, and operational practices.

Illustration of a typical utility-scale wind turbine drivetrain. The hub is connected to a main bearing, which is attached to the main shaft. This is connected to the gearbox, which is connected to the brake, high-speed shaft and, finally, the generator. All of this sits on the bedplate.


  1. Condition Monitoring (CM) is defined as the process of monitoring a parameter of the condition in machinery such that a significant change is indicative of a developing failure.
  2. Wind Stats Newsletter, 2003–2009, Vol. 16, No. 1 to Vol. 22, No. 4, Haymarket Business Media, London, UK.
  3. P. Veers, Databases for Use in Wind Plant Reliability Improvement, 2009, Wind Turbine Condition Monitoring Workshop, October 8–9, 2009, Broomfield, CO.

Active Power Control from Wind Power Workshop on the Web

Participants from industry, universities, and DOE national laboratories met at the Active Power Control from Wind Power Workshop, held on January 27, 2011, in Boulder, Colorado.

Discussions centered on grid-friendly features of active power control from wind turbines and wind plants. Various perspectives, from regulators and system operators to manufacturers and wind owner/operators, were presented in four sessions. The workshop focused on active power controls, with an emphasis in the areas of inertial response, primary control (frequency response), and secondary control (automatic generation control regulation). These types of control can assist in power system operations by ensuring that generation is balanced against electricity demand.

Results from the workshop will help guide research being conducted at NREL, and the Electric Power Research Institute (EPRI), as well as at universities, utilities, independent system operators (ISOs), and manufacturers. Since many utilities and ISOs have begun to evaluate the potential for new standards and policies that relate to these types of controls, it is important that they have the best information available.  A detailed overview of the workshop proceedings was sent to more than 100 key industry stakeholders.

A few of the key follow-up issues are as follows: Do we need a new vernacular or does the existing terminology still work (e.g., does the term 'inertia' still work)? Have we determined what the right goal is yet? Of the response categories, which will need a wind response first, which will cost most to provide from wind, and overall, which will be the most important product?

In addition to the workshop, NREL's transmission and grid integration group, EPRI, the Colorado School of Mines, and other industry members participating in a two-year project, Active Power Control from Wind Power, have made their information publically available on NREL's Wind Systems Integration website.

The joint project involves power system simulation studies that determine the benefits, steady-state impacts, and transient responses of the power system, with wind providing active power control. Through simulations and active field tests on the large wind turbines at the National Wind Technology Center, the project evaluates responses and provides related analyses to project stakeholders.

NREL's Transmission and Grid Integration Group Provides Significant Contributions to Wind Integration

Variable resources are expected to grow substantially throughout North America. The North American Electric Reliability Corporation (NERC)(1) projects that more than 260,000 MW of new variable resources will be added to the North American bulk power system in the next decade.

Understanding how to smoothly integrate these variable resources into the bulk power system and how they will influence reliability is becoming increasingly important. To efficiently integrate wind resources, significant changes in current methods are required. In 2008, NERC created the Integration of Variable Generation Task Force (IVGTF), which formalized the need within NERC to address this issue, and created an authoritative body to provide expert guidance. The Task Force examines philosophical and technical considerations for integrating variable resources into the interconnection and provides specific recommendations for practices and requirements, including reliability standards that cover operations planning and real time operating timeframes.

NREL's Michael Milligan co-chairs the Probabilistic Techniques Team of the IVGTF with Mark O'Malley, an NREL consultant and professor at University College Dublin. This team has produced two reports which have been approved by NERC's Planning Committee:

The team is now working on a third report, which will address probabilistic methods for planning and operation that are not included in the first two reports.

NREL consultant Brendan Kirby leads the Operating Practices sub-team. This group recently completed a report on Operating Practices, Procedures, and ToolsPDF that was approved by NERC's Operating Committee.

A recent presentation to the IVGTF by Michael Milligan, Methods to Model and Calculate Capacity Contributions of Variable Generation for Resource Adequacy Planning (IVGTF1-2): Additional DiscussionPDF, addresses specific actions, practices and requirements, including enhancements to existing or development of new reliability standards.


  1. 2009 Long-Term Reliability AssessmentPDF

Recent NWTC Publications

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