Study to detailed airflow through wind farm

NREL test pads

These are a few of NREL's test turbines at it's facility near Boulder Colo.

To improve wind farm energy production, NOAA (National Oceanic and Atmospheric Administration) researchers are launching a study to make visible the invisible “wakes” produced behind wind turbines. Wind-farm designs have long known that wind turbine rotors generate ripples, waves, and other atmospheric disturbances downstream of turbines. “The turbulence can damage turbines downstream, and harm productivity,” said Bob Banta, an atmospheric scientist with NOAA’s (ESRL) in Boulder, Colo.
Banta and colleagues from ESRL, the (CU) at Boulder, the U.S. Department of Energy’s National Renewable Energy Laboratory, and Lawrence Livermore National Laboratory have set up an experiment south of Boulder  to create 3D portraits of wind speeds and directions in turbine wakes.
Wind turbines —some with rotor tips that reach up 150m— stand ready to harness wind energy at NREL’s. The prevailing winds sweep east over the mountains and are funneled through Boulder’s Eldorado Canyon, right to the Wind Technology Center. “The wake effect has been modeled in wind tunnel studies and numerical models,” Banta said, “but the atmosphere is different, it’s more variable and complicated.” Banta spent the last several years using a high resolution scanning Doppler lidar to make detailed profiles of the atmosphere. For the turbine project, he wants to capture turbulence and other wake effects in a broad wedge of air up to 7-km long and 1-km up. The team will use the scanning lidar to take a detailed look at the atmosphere in front of and behind one of the large turbines on the NREL site: a 2.3-MW unit with a 100 m hub height, and a 95-m rotor dia.

hrdl datHigh density lidar image 300x270

The reading from a lidar, taken May 14, 1996, shows a range-time display of vertical profiles of the vertical wind acquired by HRDL in Boulder during tests. Positive velocities indicate rising air. The column of high negative velocity between 19:10 and 19:12 is a shaft of light rain. The simultaneous 30-m range resolution and 5-cm velocity resolution are unprecedented for a high repetition rate coherent Doppler lidar.

The researchers hope to capture ramp up and ramp-down events — winds suddenly gusting and abating. They will also gather data on what happens downstream when winds quickly shift directions. Other instruments will support the project, such as the “CU Windcube lidar” that measures wind speeds, directions, and turbulence in the lower atmosphere, and meteorological instruments on towers downwind.
“Current-generation wind turbines reach into a complicated part of the atmosphere,” said Julie Lundquist, project leader, professor in the Department of Atmospheric and Oceanic Sciences at CU-Boulder and a joint appointee at NREL. “If we can understand how gusts and rapid changes in wind direction affect turbine operations and how turbine wakes behave, we can improve design standards, increase efficiency, and reduce the cost of energy.”
Wind power now provides 2.3% of U.S. electricity. To facilitate increased electricity production from wind, its important to better understand the turbulent lower atmosphere and its effects on turbines and turbine arrays.
The wind wake study, the Turbine Wake and Inflow Characterization Study, fits under a Memorandum of Understanding on “Weather-dependent and Oceanic Renewable Energy Resources” signed by NOAA and the DOE in January 2011. The agreement sets up a framework for NOAA and DOE to work together on enhancing the accuracy and completeness of resource information for the effective and sustainable deployment, operation and maintenance, and the efficient use of weather-dependent and oceanic renewable energy technologies and infrastructure. The wind wake study was primarily funded by DOE, NOAA and CU-Boulder and involves a team led by:

  • Robert Banta and Alan Brewer, Chemical Sciences Division, ESRL
  • Yelena Pichugina, Cooperative Institute for Research in Environmental Sciences
  • Julie Lundquist, CU-Boulder, NREL National Wind Technology Center
  • Neil Kelley, NREL National Wind Technology Center, and
  • Jeff Mirocha, Lawrence Livermore National Laboratory

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