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NREL and Sandia National Laboratories to Sharpen Wind Farm Turbine Controls

April 1, 2016

Researchers at the Energy Department’s National Renewable Energy Laboratory (NREL) are working to make the “brains” of a wind farm smarter and more efficient.

Senior Research Engineer Paul Fleming along with Postdoctoral Researcher Pieter Gebraad and a team from the National Wind Technology Center (NWTC) at NREL have designed control systems—the brains—which coordinate the controllers of individual turbines.

They soon will be validating the program in collaboration with Sandia National Laboratories at Sandia’s Scaled Wind Farm Technology Facility (SWiFT) in Lubbock, Texas. The project is part of Atmosphere to Electrons (A2e), a multiyear, multilab research initiative to reduce the cost of wind energy by understanding the physics governing wind flow into and through wind farms.

Starting this spring, the trials on subscale turbines at SWiFT will be the next phase of the testing that began at NREL with detailed computations and wind turbine modeling. The NREL controls team have been evaluating their control theory in simulations, using fluid dynamics simulations on Simulator fOr Wind Farm Applications, or SOWFA, an NREL tool to investigate wind turbine and wind plant performance under the full range of atmospheric conditions and terrain.

“They’ve shown there are really some great opportunities to control a wind plant in a way that moves the wind flow within the plant to unblock some of the downstream turbines from the upstream,” said Paul Veers, chief engineer at the NWTC.

Controls determine—based on what a turbine senses—how it is going to operate and which direction it should point. If a turbine just functioned autonomously, it would point exactly into the wind. But if the wind plant is controlled as a whole, the control system could factor in not only which direction the wind is coming from but the locations of neighboring turbines. That ability allows turbines to steer off to the side a little bit, which can skew wakes—helping downwind turbines and the entire farm to achieve a higher total efficiency.

One reason NREL is involved in the project is because of its extensive experience using light detection and ranging (lidar), a sensing technology that that can measure the wind speed at remote locations using lasers. This experience will be used to “see” the wake of one turbine and how it displaces downwind and impinges on other turbines.

“We are working together with Sandia to design a mount for a lidar to point out of the rear of the nacelle of the wind turbine to measure the wake behind the rotor. In order to capture the wake deflection, the mount design will need to allow the lidar to swivel left and right, which is not trivial given the tight space inside the nacelle of the wind turbine,” said Field Test Engineer Andrew Scholbrock. “We’re also working with our own computational science teams to model specific lidar inside fluid dynamics simulations, and to find out what we expect to see from the lidar in the field,” Fleming said.

The project is promising, leveraging expertise at both national laboratories. “The planning and preparation for the upcoming wind plant controls experiment has greatly benefited from the complimentary capabilities and resources of the NREL and Sandia groups,” said Sandia’s Brian Naughton, the principal investigator on the project. “The combined experience of the team in wind turbine controls, computational modeling, and field experimentation will yield a valuable public repository of high-quality data for the broader research community.”

The SWiFT facility has three heavily instrumented and modified variable-speed variable-pitch Vestas V27 turbines and two 60-meter anemometer towers. The first two turbines are spaced 3 rotor diameters apart, perpendicular to the oncoming wind, and the third turbine is located 5 rotor diameters downwind.

Fleming said that this project is envisioned as a multiyear effort. By incorporating system-lev¬el operating strategies that rely on active flow monitoring and plant flow control, researchers and wind farm designers can build the foundation for future development of wind plant technology that adds even more intelligence. Such research into “brainy” wind farms offers the possibility of a whole new range of wind plant layouts and increased efficiencies.

—Kelly Yaker