In the Wake of the Wind Turbine

CIRES and NOAA scientists study the wake effect of wind turbines to improve efficiency and reduce damage

On the southern edge of Boulder County, Colo., Eldorado Canyon carves a gap through the Rocky Mountains. The canyon funnels prevailing winds, which sweep east over the mountains, smack into the National Wind Technology Center.

Wind turbines, some taller than a 30-story building, stand waiting at the site, which is part of the Department of Energy's National Renewable Energy Laboratory (DOE's NREL).

The turbines not only convert the energy from the wind into wind power, but the rotating blades produce wakes – invisible ripples, waves and other disturbances downstream. Scientists from the Cooperative Institutes for Research in Environmental Sciences (CIRES) and NOAA launched a study of those wakes early this month, with an eye toward improving the productivity of wind farms.

“This turbulence can damage turbines downstream, and harm productivity,” said Bob Banta, an atmospheric scientist with NOAA's Earth System Research Laboratory (ESRL) in Boulder and a leader of the study along with Yelena Pichugina, a research scientist at the Cooperative Institute for Research in Environmental Sciences (CIRES).

Pichugina , Banta and Alan Brewer from NOAA's Earth System Research Laboratory (ESRL) in Boulder, and colleagues from NREL have set up an experiment to make a study of wakes created by wind turbines. The goal of this short term-experiment, funded by the University of Colorado at Boulder's Renewable and Sustainable Energy Institute, is to record the important aspects of the wakes created by wind turbines, using NOAA's high-resolution, scanning Doppler lidar.

This experiment is conducted now along with a DOE funded experiment, Turbine Wake and Inflow Characterization Study (TWICS), which is aimed an integrating turbine inflow and wake observations into a wind energy forecasting model.

“Wake study is very important not only for turbine designers but wind farm developers,” Pichugina said. “Turbines that are located behind other turbines can get less energy, so they will generate less power.”

The NOAA Remote Sensing Group has used the Doppler lidar for almost two decades to study wind speeds and directions in the atmosphere. For the turbine project, the scientists hope to capture turbulence and other wake effects in a broad wedge of air up to 7 km (4.3 miles) long and 1 km (3,280 feet) high.

“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.”

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-megawatt graceful giant that stretches 100 m (328 ft) to the central hub and 145 m (492 feet) to the top of a blade.

The researchers hope to be able to capture the effects of ramp up and ramp down events, when winds suddenly gust high or die down, and they will gather data on what happens downstream when winds shift direction quickly.

“This generation of wind turbines are stretching up into a complicated part of the atmosphere,” said Julie Lundquist, TWICS project leader and a professor in the Department of Atmospheric Sciences at the University of Colorado-Boulder and a joint appointee at the National Renewable Energy Laboratory.

“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.”

By the end of 2010, wind power provided 2.3 percent of U.S. electricity, up from 1.8 percent the previous year. Researchers have argued that to attain the DOE goal of “20 percent by 2030,” the turbulent lower atmosphere – and its effects on turbines and turbine arrays – must be better understood.

“We have to do everything in our power to promote wind energy,” Pichugina said. “This type of energy is clean and it will provide independence from foreign oil.”

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Leaders of TWICS, the Turbine Wake and Inflow Characterization Study:

  • Yelena Pichugina, Cooperative Institute for Research in Environmental Sciences
  • Robert Banta and Alan Brewer, NOAA Earth System Research Laboratory
  • Julie Lundquist, University of Colorado at Boulder, National Renewable Energy Laboratory National Wind Technology Center
  • Neil Kelley, National Renewable Energy Laboratory National Wind Technology Center
  • Jeff Mirocha, Lawrence Livermore National Laboratory

Contact: Jane Palmer, CIRES, 303-492-6289, Jane.Palmer@colorado.edu