Device and Component Testing
The National Renewable Energy Laboratory (NREL) houses the nation's premier laboratory facilities for validating offshore water power devices and maintains a staff of offshore-trained engineers and technicians that conduct a wide range of field measurements to verify system performance and dynamic responses. Applying 35 years of expertise in wind turbine evaluation, NREL has the capabilities to obtain high-resolution measurements in the laboratory and open-water validation sites.
With the support of the U.S. Department of Energy, NREL has helped the wind industry advance by introducing customized sensors and instrumentation; conducting landmark experiments, such as the National Aeronautics and Space Administration, Ames, unsteady aerodynamics experiment; and leading industry research groups such as the wind Gearbox Reliability Collaborative. NREL is now taking its past successes and applying its years of experience and validation capabilities to advance the water power industry. Capabilities directly applicable to water power technologies include:
As the newest member in our nation's renewable energy portfolio, the marine and hydrokinetics (MHK) industry is developing concepts for dozens of devices that can turn the kinetic energy in ocean waves and currents into clean electricity. For these new technologies to mature to commercial readiness, research and validation are essential to mitigate technical, environmental, and financial risks.
To advance the MHK technology and provide necessary data to feed future designs and field expansion, NREL is developing a Modular Ocean Instrumentation System (MOIS) that will provide device companies with the field measurements they need to better understand system operation and performance. In addition to system performance, NREL's MOIS provides the measurements needed for resource assessment, siting, evaluation, monitoring, demonstration, and eventual certification for a broad range of offshore renewable energy devices, resources, and locations.
NREL's MOIS is built with a commercial off-the-shelf, modular, and scalable infrastructure and LabVIEW software with individual software modules developed for separate functions and measurements. The reusable code can implement new features as needed and enables the MOIS to be rapidly customized to meet the unique measurement needs of individual deployments.
NREL facilities at the National Wind Technology Center (NWTC) support the validation of water power devices and components needed to simulate operational performance of designs from concept to production machine. NREL staff engineers and technicians provide water power industry manufacturers, developers, and operators with the turbine and component evaluation expertise needed to validate designs and quantify performance. Component and full-scale structural assessment is a valuable and necessary means of demonstrating system reliability. Evaluating components in the laboratory environment provides the data required to validate in-water designs. At the NWTC, laboratory evaluation rigs are designed and configured to apply realistic boundary conditions and the forces, moments, and torques needed to properly simulate in-water loading in a laboratory environment. Validation articles can be heavily instrumented to measure key design parameters including stress, strain and displacement. Designers need to measure key values to validate models and ensure their designs will meet the criteria for a full lifetime of operation. Typical component structural evaluation includes:
- Property validation
- Dynamic characterization
- Strength validation
- Fatigue analysis
Property validation evaluates inherent structural properties, including mass and center of gravity. Precise measurements of these parameters are critical to ensure compliance with design goals.
Dynamic characterization of a component or complex structure is accomplished through modal validation. Modal validation provides designers with the natural frequencies, damping values, and mode shapes of the component or system. These data are used to validate distributed system parameters including mass and stiffness. The parameters are critical inputs to dynamics models. Parameter tuning plays an important role in designing structures by minimizing dynamic loads and increasing lifetime. Modal validation is conducted by installing an array of accelerometers on the structure, then measuring the response to a known input from impulse and random excitations.
Static strength validation assesses design parameters and demonstrates the ability of a component or system to handle extreme design load cases. These load cases simulate the response of the structure while operating and parked to extreme conditions such as inflow direction changes, 50 or 100-year flow conditions, and loss of grid connection. These events can be simulated in the laboratory by properly constructing representative boundary conditions then applying loads simulating the flow or forcing function through hydraulic actuators, cranes, or winches. Multi-axial loading at independent locations is sometimes needed to properly simulate a given load case. Loads are applied while measuring specific data, including strain and displacement. Strain is used to evaluate the stress on a component, and displacement measurements quantify the stiffness of a component.
Fatigue validation demonstrates the durability of a component or system. Typically fatigue assessments will load a component with millions of load cycles applied over several weeks or months. Fatigue validation reveals design and manufacturing problems at an early stage of development and leads to overall improvements in design, performance, and reliability while reducing the risks inherent when commercializing new designs.
Fatigue loads are introduced to the structure through hydraulic actuators. Specialized component validation of blades may be accomplished by applying loads at the system's natural frequency to decrease the duration. Displacement and strains are typically measured during validation. Structural health monitoring and nondestructive evaluation techniques, including acoustic emission and thermography, are employed to further assess the article's health.
NREL is accredited by the American Association of Laboratory Accreditation (A2LA) to validate to the IEC 61400-23 wind turbine blade test standard. NREL has operated wind turbine blade structural validation facilities since 1990 and during this time has assessed hundreds of wind blades. The NWTC has pioneered the development of innovative validation systems that improve accuracy and decrease the time of a typical validation program. This expertise is being applied to the development of methods and protocols for assessing marine and hydrokinetic devices.
Dynamometers are an effective means for validating new drivetrain designs. NREL has dynamometer validation facilities that can assess drivetrains and components with capacity ratings of less than 10 kW and up to 5 MW. NREL's dynamometer validation facilities can assess a variety of components and subsystems, including generators, gearboxes, mechanical or electro-dynamic brakes, power electronics, control systems, and software.
Validation objectives of manufacturers and design engineers may include performance, system integration (generator, power electronics, and grid), software development, or accelerated life validation.
Controllable Grid Interface
NREL 's new controllable grid interface (CGI) system at the NWTC that will significantly reduce the time to conduct and cost of conducting certification validation for renewable technologies. The CGI will be the first facility in the United States to have fault simulation capabilities and that allows manufacturers and system operators to conduct certification assessments in a controlled laboratory environment. It is the only system in the world that is fully integrated with two dynamometers and has the capacity to extend that integration to renewable energy devices in the field and to a matrix of electronic and mechanical storage devices, all of which are located within close proximity on the same site. The CGI's capabilities include:
- Voltage fault ride-through
- Frequency response
- Continuous operation under unbalanced voltage conditions
- Grid condition simulation (strong and weak)
- Grid voltage distortions simulation
- Reactive power, power factor, voltage control validation
- Protection system assessment (over- and under-voltage and frequency limits)
- Islanding operation
- Sub-synchronous resonance conditions
- 50 Hz validation.