Inspired by Palm Trees, Scientists Develop Hurricane-Resistant Wind Turbines | CU Boulder today

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Banner image: Researchers from the NREL Flatirons campus, posing in front of the two-bladed SUMR-D in the background. Left to right: Lucy Pao and Mandar Phadnis of CU Boulder, and Dan Zalkind of NREL. (Credit: Kelsey Simpkins/CU Boulder)

Wind technology is growing, literally. Today’s offshore wind turbines can soar more than 490 feet above the ground, their rotating blades producing up to 8 megawatts (MW) each, or about enough to power 4,000 homes in the United States.

But with their growing size comes challenges. Off the east coast, where there are offshore wind turbines in the United States, increasingly powerful Atlantic hurricanes pose risks to the structures themselves and to the future of wind energy. To make these turbines more resistant to hurricanes, a team of CU Boulder researchers took inspiration from nature and rotated the turbine.

“We’re very bio-inspired by palm trees, which can survive these hurricane-like conditions,” said Lucy Pao, Palmer Endowed Chair in the Department of Electrical, Computer and Energy Engineering.

Traditional wind turbines face the incoming wind, and to avoid being blown into the tower, their blades must be stiff enough. It takes a lot of material to build these relatively thick and massive blades, which drives up their cost. The turbine blades on the downwind rotors, however, are pointed away from the wind, so there is less chance of them hitting the tower when the winds pick up. This means they can be lighter and more flexible, requiring less material and therefore less money to be made. These lee blades can also bend rather than break in the face of strong winds, much like palm trees.

Over the past six years, in collaboration with collaborators from the University of Virginia, the University of Texas at Dallas, the Colorado School of Mines and the National Renewable Energy Laboratory, Pao’s team has collaborated to develop the SUMR (Segmented Ultralight Morphing Rotor) turbine, a two-bladed downwind rotor to test the performance of this lightweight concept in action. June 10 at American Conference on ControlCU researchers presented the results of a new four-year study of real-world data from testing their 53.38-kilowatt demonstrator (SUMR-D) at the Flatirons campus of the National Renewable Energy Laboratory (NREL), just south of Boulder, Colorado.

They found that their wind turbine operated consistently and efficiently during periods of maximum wind gusts, a satisfactory result.

“The blades are made to be lightweight and very flexible, so they can align with wind loads. This way we can reduce the cost of the blades and drive down the cost of power,” said Mandar Phadnis, lead author of the new study in Proceedings of the 2022 American Control Conferenceand a graduate student in electrical, computer and energy engineering.

This innovative work could not have come at a better time. Not only does climate change require that we rapidly develop more cost-effective and reliable renewable energy, but rising global temperatures are also likely to intensify hurricanes.

Hurricane activity this year in the Atlantic is expected to be above average, with NOAA’s Climate Prediction Center estimating up to six major hurricanes with winds of 111 mph or more from June 1 through November 30.

Lucy Pao and the wind turbines

Top: Close-up of the 53.38-kilowatt demonstrator (SUMR-D) on the Flatirons campus of the National Renewable Energy Laboratory (NREL), just south of Boulder, Colorado. Bottom: Lucy Pao at the NREL Flatirons campus, with SUMR-D directly to her right. (Credit: Kelsey Simpkins/CU Boulder)

The hidden brain of a turbine

One of the trickiest parts of wind power generation is managing too little or too much wind at once. When the wind speed is too low, a wind turbine cannot produce a useful amount of energy. When the gusts are too fast, they can push the limits of a turbine’s capacity, causing it to shut down to prevent system overload.

Wind speed inconsistency has plagued wind power since its inception; wasted time spent shutting down the system leads to less energy generated and less efficient production.

Key to Pao’s innovative contributions are improvements to the controller, the part of the turbine that determines when to be more or less aggressive in power generation.

“We like to think of the controller as essentially the brains of the system,” said Pao, the study’s lead author and fellow at the Renewable and Sustainable Energy Institute (RASEI).

This hidden brain aims to produce efficient wind power at low cost and with low wear. To do this, the feedback controller uses measurements of system performance and then adjusts to better improve performance, Pao said.

The yaw controller makes sure the turbine is pointing in the right direction, the blade pitch controller determines the direction of the blades (based on wind speed), and the generator torque controller decides how much power to draw of the turbine and on the network. Although it controls the physical components of the turbine, these controllers are essentially a software algorithm that tells the motors what to do.

Pao’s group doesn’t just spin the turbine to reduce damage from high winds, but works behind the scenes on its software to maximize the system’s ability to keep running during peak winds.

“Our work attempts to predict the probability or likelihood of peak wind gusts occurring, and then attempts to mitigate the peak speeds by acting before they occur,” Phadnis said.

NREL’s Flatirons campus was the perfect place to test this in action, as it is strategically placed to receive the strong winds that cross Highway 93 and over the mesa, having been funneled through Eldorado Canyon directly at the ‘west.

There, the researchers found that, even through extensive experimental testing, the generator’s peak speeds were below the threshold for their operational controller to keep the turbine running.

In a separate collaboration, Pao and his research group worked with the University of Oldenburg in Germany to assess the usefulness of sensors that scan in front of the turbine to measure incoming wind and advanced controllers that command the turbine to react. proactively.

Develop global wind energy

While downwind or two-bladed wind turbines like the SUMR-D may not dominate the wind power industry, by performing these multi-year real-world tests, researchers are able to better understand what that might be possible, Pao said.

The control algorithms they developed could also be applied to traditional three-bladed and wind turbines, which still dominate the onshore and offshore markets.

Wind turbine graphic

Different sizes of onshore and offshort wind turbines, compared to famous landmarks for reference. (Credit: Chao Qin and sumrwind.com)

“The advantage of the downwind configuration, however, really comes through when you get to large-scale turbines, and those are primarily for offshore,” Pao said.

Pao’s group is already approaching these great peaks: together with their collaborators, they have designed and modeled (but not experimentally tested) large-scale 25 MW and 50 MW SUMR (downwind) offshore turbines.

Ultimately, she believes a combination of improved controllers, lighter and more resilient materials, and strategic turbine configurations could allow giant offshore turbines to leapfrog the competition. They are not only more cost effective and energy efficient, allowing for one large turbine instead of several smaller ones (which would reduce installation and maintenance costs), and able to capture higher wind speeds higher off the ground, but they could also withstand the more severe weather conditions to come.

“Wind turbine blades are typically designed to last at least 20 years, and we want our new concept blades to achieve similarly long lifespans,” Pao said.

This study was funded by the U.S. Department of Energy’s Advanced Research Projects Agency – Energy (ARPA-E) and conducted in partnership with the National Renewable Energy Laboratory (NREL).


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