Up to Wind Speed — June 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:
NREL's new controllable grid interface (CGI) provides the first full-scale, wind energy oriented, electrical grid simulation capability in the United States. The facility is now under construction at NREL's NWTC and is expected to be online in late 2012. The facility encourages market acceptance of wind energy generation systems by enabling testing on, and certification of, the electrical characteristics of megawatt-scale wind turbines.
The CGI connects a wind turbine under test to the electrical grid, providing testing and validation capabilities. It provides industry with the ability to verify that a turbine design can meet all requirements for connection to the grid, including low-voltage ride through (LVRT) tests that are required in the United States and abroad. Additionally, the system will allow U.S. manufacturers to test 50 Hz turbines that are intended for market in the European Union, China, and other parts of the world. The research community will also be able to use the CGI to verify the predictive software used in turbine design.
The system is based on 7-MW continuous rated power circuits that are fully regenerative so they can pass power back to the grid from the turbine under test. The test article side of the system is rated at 14 MW, so it can support the extremely high currents that are present for short times during LVRT testing. For the wind turbine, the simulator acts as an electrical grid at 60 Hz, with three-phase power at 13,200 volts. Under an operator's command, the wind turbine controls would detect abnormal frequency, voltage, and fault (short circuit) conditions to test critical aspects of the turbine's control and protection system. These abnormal conditions will not be propagated to the utility side of the grid simulator. Similarly, tests can be conducted for PV and/or storage systems.
The electrical topology of the 7-MVA CGI consists of multiple voltage source converters. The line side converter is connected to the utility's 13.2-kV line, and two test article side converters are connected in parallel for increased short circuit current capability.
Specific tests that can be conducted using the NWTC CGI are:
The facility will be integrated with the NWTC's new 5-MW dynamometer as well as the existing 2.5-MW dynamometer. It may be used by other facilities and technologies within the sustainable energy research community.
The Energy Department recently released a new wind resource map compiled by the National Renewable Energy Laboratory (NREL) and AWS Truepower that combines land-based with offshore resources. The new map is the first to provide wind developers and policy makers with a seamless representation of the wind resources measured at an 80-m height for all 50 states. It was compiled using AWS Truepower's data at a spatial resolution of 2.5 km and interpolated to a finer scale.
The new map, posted on NREL's Wind Resource Assessment web page, allows developers and policymakers to easily compare land-based with offshore wind resource potentials. For example, it shows that the offshore wind resource of the Great Lakes is comparable to that found in the windier areas of the western plains states. It also demonstrates the greater potential for offshore resources to provide for the electricity needs of the heavily populated coastal regions.
Read more about the Energy Department's Wind Program wind resource assessment and characterization efforts. For state-specific maps of offshore wind resources at 90 m and land-based resource maps at a variety of heights ( including residential and community applications), visit the Wind Powering America website — Maps & Data.
The University of Colorado at Denver and the Wirth Chair awarded the Energy Department's National Renewable Energy Laboratory (NREL) a Wirth Chair Sustainability Award for its work on the Wind for Schools Project. NREL manages the Wind for Schools project as part of its support to the Department's Wind Powering America initiative. NREL and its project partners, the Colorado governor's energy office and the Colorado State University Wind Application Center, were recognized at an awards luncheon on April 25th.
This year marks the 13th anniversary of the Wirth Chair Awards that celebrate the "Creators of a Sustainable Future." The Wirth Chair in Sustainable Development at the School of Public Affairs at the University of Colorado at Denver is named for former U.S. Senator and Under Secretary of State, Timothy E. Wirth. It honors environmental and sustainable development achievements across Colorado.
The Energy Department's Wind Powering America initiative has helped to launch the Wind for Schools project in 11 states, including Colorado. The program provides training in wind design and implementation for engineering students at the universities and gives K-12 students, teachers, and the community a hands-on opportunity to learn about wind as well.
In 2009, the Colorado Wind Application Center at Colorado State University (CSU) in Fort Collins and the Colorado governor's energy office selected six rural Colorado schools to participate in the Wind for Schools project. The governor's energy office provided a $5,000 grant for each school to help purchase and install a Skystream 3.7 wind turbine. These turbines provide the basis for learning about wind in the school.
NREL manages the program, funds the wind application centers through subcontracts, and trains teachers and community facilitators that work with the K-12 schools to build community support. NREL worked with CSU to develop its curriculum and with the National Energy Education Development Project to develop a K-12 curriculum.
Learn more about Wind for Schools.
Modern control applications depend on accurate turbine models for successful load mitigation and energy capture performance. Model uncertainties and turbine operation away from control design points degrade controller performance. Design of controls that are robust to meet the uncertainties in the wind turbine models and operating parameters is critical to realizing intended controller performance. Collaborative efforts between NREL and international research organizations compare robust control concepts, evaluating and testing advanced feed-forward Light Detection and Ranging (LIDAR) systems and feed-forward control algorithms.
NREL and Delft University of Technology (TU-Delft), in the Netherlands, share a mutual interest in the development and testing of advanced robust controls for improved turbine load mitigation and energy capture in the midst of modeling uncertainties. Through a Cooperative Research and Development Agreement (CRADA), NREL and TU-Delft are collaborating on the design of robust controls. An evaluation of robust control concepts will be performed through field tests on the National Wind Technology Center's (NWTC) three-bladed, Controlled Advanced Research Turbine (CART3) and the performance will be documented through a controller comparison paper.
The control of wind turbines during extreme wind events is critical to reducing extreme loads and increasing turbine reliability. Under a CRADA with Energy Center of the Netherlands (ECN), NREL will perform a comparison study of the performance of the NREL baseline wind turbine controller on the CART3, against the same controller augmented with the ECN Sustainable Controller module. The collaboration will include the collection of field test data at the NWTC, analysis of the data, and a joint publication of the benchmark results.
Working together under a Memorandum of Understanding with the University of Stuttgart, NWTC researchers are evaluating advanced feed-forward LIDAR controls. Feed forward controls measure the flow field in front of a turbine and adjust its systems in advance of changing winds, enhancing the turbine's yaw, rotor, and generator controllers to improve energy capture. New sensors such as LIDAR-based wind measurement systems use advanced feed-forward control algorithms that mitigate loads. Feed-forward controls are especially effective in detecting and mitigating extreme events that cause high loads and reduce energy production. With feed forward, such events can be sensed in advance to prepare the controllers to reduce loads or to ride-through extreme events in a de-rated mode without shutting down. The University of Stuttgart LIDAR was mounted on the 2-bladed Controls Advanced Research Turbine (CART2) in the spring of 2012. Feed-forward control algorithms implemented and field tested on the CART2 will analyze measured wind speed data to improve control performance. In addition, Stuttgart will assist in feed-forward controls implementation and field testing using the Catch the Wind's LIDAR mounted on the 3-bladed Controls Advanced Research Turbine (CART3).
Most turbine control systems depend on wind speed and direction measurements from instruments located on the nacelle of a wind turbine. These measurements are usually inaccurate, because they are distorted by the wake of the turbine immediately behind the rotor. LIDAR sensors can provide more accurate wind speed information to wind turbine control systems. In partnership with Catch the Wind (CTW), NREL is evaluating the CTW's Vindicator LIDAR for use in improving control algorithm performance. It provides the wind turbine controller with wind speed information upwind of the machine before wind gusts impact the turbine.
NREL and CTW have mounted a Vindicator LIDAR unit to the nacelle of the CART3. This LIDAR scans ahead of the turbine, avoiding the distortion of wind speed measurements due to interference of the rotor's wake. Field tests of advanced feed-forward control algorithms are being conducted. The ability of the controller to mitigate critical turbine loads is being carefully assessed and its improvement to control performance is being evaluated.
In addition, evaluations of different LIDAR configurations for feed-forward control applications will be performed with CRADA partner DTU-Wind Energy. In collaboration with DTU-Wind Energy, NWTC researchers will field test advanced feed-forward LIDAR-based controllers on the NREL CART3 machine.
Assessments of this technology may prove that providing real-time wind-speed information to advanced load mitigation control algorithms has performance and energy capture benefits. In addition, it could allow engineers to design large multi-megawatt machines with lighter more flexible components, removing expensive material from the structures. Costs may be further reduced through load mitigation and increased fatigue lifetime.
Premature gearbox failures have a significant impact on the cost of wind farm operations. In 2007, NREL initiated the Gearbox Reliability Collaborative (GRC). The project combines analysis, field testing, dynamometer testing, condition monitoring, and the development and population of a gearbox failure database in a multi-pronged approach to determine why many wind turbine gearboxes do not achieve their expected design life—the time period that manufacturers expect them to last.
The collaborative of manufacturers, owners, researchers, and consultants focuses on gearbox modeling and testing and the development of a gearbox failure database. Collaborative members also investigate gearbox condition monitoring techniques. Data gained from the GRC will enable designers, developers, and manufacturers to improve gearbox designs and testing standards and create more robust modeling tools. The Gearbox Reliability Collaborative (GRC) website offers wind turbine manufacturers and researchers accessible information on the latest results and reports by the collaborative.
The GRC project developed two identical, heavily instrumented representative gearboxes. Knowledge gained from the field and dynamometer tests conducted on these gearboxes builds an understanding of how the selected loads and events translate into bearing and gear response. The GRC investigates condition monitoring methods to improve turbine availability. In addition, the GRC evaluates the current wind turbine gearbox gear and bearing analytical tools and models, develops new tools and models, and recommends improvements to design and certification standards. Information gained from the various projects within the GRC led to the development of the GRC Failure Database. This database provides the means for multiple partners to document root cause analyses in a tool that identifies key failure trends. Once identified, the trends allow researchers to focus on the solution to gearbox challenges and the database provides a method to measure improvements.
NREL and its GRC partners have been able to identify shortcomings in the design, testing, and operation of wind turbines that contribute to reduced gearbox reliability. In contrast to private investigations of these problems, GRC findings are quickly shared among GRC participants, including many wind turbine manufacturers and equipment suppliers. The GRC website makes the findings public for use throughout the wind industry.
In February, the GRC members met at the National Renewable Laboratory in Golden, Colorado, to discuss the completion of Phase 2 testing, which included hundreds of hours of steady state and dynamic loads testing in the NWTC's 2.5-MW dynamometer test facility. Selected data sets have been released to the GRC partners to aid in data validation and modeling assumption convergence. The February meeting included planning of Phase 3 modeling, analysis, and testing activities to be conducted in the remainder of 2012 and in 2013.
NREL's 2010 Cost of Wind Energy Review presents the best available information on the cost of wind energy in 2010, along with a summary of historical trends and future projections. This information is very important to decision makers that need to compare costs of different generation resources. Although the 2010 report does not compare wind energy to other technologies, it does calculate the levelized cost of energy (LCOE) for both land-based and offshore wind energy technologies using four major inputs; (1) installed capital cost, (2) annual operating expenses, (3) annual energy production, and (4) a fixed charge rate.
Comparing the LCOE for different technologies is most effective when one understands the four major inputs and how they fit together. This is especially important for a technology such as wind energy because of the constant tradeoff between maintaining or reducing capital investment and increasing energy capture.
NREL found that the range of LCOE for land-based wind is $58–$108/MWh, the range of LCOE for offshore wind is $118–$292/MWh, and that costs can vary widely depending on several key factors. The largest ranges are seen in capital cost and financing for both land-based and offshore projects and include capacity factors for land-based projects.
NREL plans to review and update these costs on an annual basis as consistently calculating the LCOE helps maintain a market perspective and develop a better understanding of the costs of individual components to the wind generation system.
Deployment and market transformation (D&MT) activities at the National Renewable Energy Laboratory (NREL) encompass the laboratory's full range of technologies, which span the energy efficiency and renewable energy spectrum. NREL staff educates partners on how they can advance sustainable energy applications and also provides clients with best practices for reducing barriers to innovation and market transformation.
The Deployment and Market Transformation at NREL quarterly newsletter highlights D&MT activities from the past three months. Features include major partnership projects, new websites, updates to our models and tools, and our latest publications.
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