Researchers are seeking ways to mitigate wind patterns that could limit the output or cause excessive wear on the hundreds of wind turbines planned off the Atlantic Coast.
The National Renewable Energy Laboratory said last week that it and the General Electric Global Research Center (NYSE:GE) are applying ultra-powerful supercomputer modeling to the low-level jet stream (LLJ) patterns that exist on the Outer Continental Shelf along the eastern U.S.
The region, with its steady wind and shallow waters, is regarded as ideal for wind power generation, but there is little observed data on actual performance: OSW in the U.S. so far consists of two test turbines off the coast of Virginia and a pioneering Rhode Island wind farm whose five 6-MW turbines are much smaller and much closer to shore than what is planned to come.
The blade sweep of the largest OSW turbines can approach 10 acres of airspace and reach almost 900 feet above the sea surface. LLJs can occur at this altitude along the Atlantic Coast, and they can be strong, NREL said.
The researchers in their study said that depending on the detection criteria used, LLJs can be observed at least 2 to 7% of the time in the New York Bight, where multiple wind projects are envisioned. But the LLJ is categorized as a nonconventional wind event, they said. Its characteristics are not well understood, and it is not currently considered in some annual energy production calculations.
With exascale computer simulations, the research team has shown a propensity for LLJs to cause a severe wake-induced decrease in wind turbine power output and an increase in load on turbine blades. This could cause excessive wear and tear on the equipment, lower its efficiency and even cause shutdowns, NREL said.
But the simulations are also pointing toward strategies to mitigate the impacts of LLJs. In a news release, the principal investigators said this is a promising development.
“Site-specific, high-fidelity simulations of wind farms are typically beyond the scope of the wind energy design process due to the sheer complexity of the science and computational modeling involved,” said Balaji Jayaraman, a senior engineer at GE Research. “However, through advances in exascale computing algorithms and models for multiscale atmospheric flows — driven by the U.S. federal research labs including NREL and powered by the world’s leading supercomputing capabilities — we’ve been able to demonstrate the feasibility of new wind turbine designs previously not possible.”
“This team was able to accomplish all the goals originally proposed back in 2019,” added NREL’s Shashank Yellapantula.
NREL is the lead lab for the U.S. Department of Energy’s Exascale Computing Project. It has been spearheading an effort to simulate the air flow around wind turbines in a large wind farm with unprecedented accuracy using the latest generation of computing.
The NREL/GE team ran simulations on five- and 20-turbine arrays in a 10-km region with 2 billion points on a grid pattern to visualize the invisible impacts of flow dynamics and make conclusions.
They found LLJs caused a significant increase in load on turbine blades. In the larger wind farm, the LLJs led to deeper wakes that reduced wind velocity and increased turbulence, reducing power output.
Derating the turbines — running them at a lower power level to limit damage — has been the common response by wind farm operators to this scenario, NREL said.
Using the data and observations gathered so far, the team is now designing strategies to reduce the impact of LLJs while maintaining higher power output.
“We’ve never had this level of detail available to us before to understand that wind farms that are designed a certain way can withstand the power of LLJ phenomena,” Yellapantula said.
Bringing emissions-free OSW online is a priority for the federal government and many states as a strategy to limit the impact of climate change.
More than two dozen OSW lease areas are designated from Massachusetts to South Carolina; construction has begun in two, and plans for several others are under review by the U.S. Bureau of Ocean Energy Management. Manufacturers meanwhile are working to improve technology and expand factory capacity.
