Turbulent Northeast poses opportunities, challenges for wind development

Source: Daniel Cusick, E&E reporter • Posted: Wednesday, August 17, 2016

The Northeast Atlantic coast has some of the world’s strongest offshore winds, according to developers who have long waited for the opportunity to build commercial-scale wind farms on the outer continental shelf from Maine and New Jersey.

But those same winds are highly volatile, posing unique challenges to those same developers, according to researchers at the University of Delaware and Stony Brook University who reviewed a decade’s worth of wind data off the Massachusetts coast.

The findings, from a team led by Cristina Archer, an environmental engineer and associate professor at the University of Delaware’s College of Earth, Ocean and Environment, show that while wind speeds are more powerful in the northeast Atlantic, they are also considerably more turbulent and unpredictable.

Such conditions, which the researchers liken to turbulence experienced in airplanes when air masses collide, will require developers to make careful decisions about the types of wind turbines to be deployed, as well as the configuration of turbines in the offshore environment.

“The advantage of these turbulent conditions is that, at the level of the turbines, these bumps bring high wind down from the upper atmosphere where it is typically windier,” Archer said of the findings, published in the Journal of Geophysical Research: Atmospheres.

“This means extra wind power, but that extra power comes at a cost: the cost of more stress on the turbine’s blades,” she said.

Archer and colleague Brian Colle of Stony Brook University’s School of Marine and Atmospheric Sciences said their findings about wind volatility could have implications for how future offshore wind farms in the region are designed and deployed.

The fact, they said, that winds are predominantly turbulent in the Nantucket Sound stands in stark contrast to data collected at European offshore wind farms in the Baltic and North seas. There, wind conditions have proved to be predominantly neutral — meaning neither too windy nor too still.

“By contrast, our study found that wind conditions at Cape Wind are unstable between 40 and 80 percent of the time, depending on season and time of day,” Archer said.

Though Cape Wind claims to be “in its … final commercial contracting stage,” federal judges struck a blow to the project in July when they ruled that U.S. environmental permits were issued unlawfully (Greenwire, July 5). Certain environmental groups have been battling the project for years, alleging impending harm to migratory bird species.

If Cape Wind prevails, however, it may have to reassess its turbine calculations: The group’s current resource assessment would have assumed a neutral atmosphere.

“In Nantucket Sound,” Archer said, “neutral is not going to cut it.”

Wind direction key

The findings could prove especially beneficial to firms like Dong Energy of Denmark, which plans to invest hundreds of millions in wind farms off the coasts of Massachusetts and New Jersey, including the planned 1,000-megawatt Bay State Wind project roughly 15 miles south of Martha’s Vineyard.

Dong is the world’s largest offshore wind energy developer, with more than 20 projects completed or under construction off the coasts of the United Kingdom, the Netherlands, Germany and Denmark. In the United States, Dong will join firms such as Rhode Island-based Deepwater Wind in delivering utility-scale wind power to the Eastern Seaboard.

Deepwater Wind’s 30-MW Block Island Wind Farm, off the Rhode Island coast, is expected to begin delivering power later this year to Block Islanders, as well as to the mainland grid via a subsurface cable. Public officials and wind energy proponents have said projects like Block Island and Bay State Wind could provide the answer to rising electricity demand in major East Coast metro areas from Boston to Washington, D.C.

The research offers one of the first looks at the complexities of atmospheric conditions for wind energy development in the United States, and it relies on a new modeling tool called IMPOWR that helped verify earlier readings taken from the Cape Wind tower in Nantucket Sound, a multi-level structure with sensors positioned approximately 65 feet, 131 feet and 196 feet above the ocean surface.

In 2013 and 2014, with funding from the U.S. Department of Energy, the research team made 19 plane flights around the Cape Wind tower to measure wind speeds, temperatures and humidity levels under varying weather conditions, as well as installing new wind and wave sensors on the tower itself.

Combining the new findings with buoy data from just above the water’s surface and historical data from Cape Wind, the IMPOWR tool “painted a surprising and yet consistent picture of the area’s wind resources,” the researchers said.

“We get the same message whether we look at the turbulence from the flights or from the sonic anemometers on the tower, or whether we consider the wind speed data alone,” Archer said. “The marine atmosphere is more likely to be unstable than neutral.”

Among the specific findings are that wind direction plays a role in whether conditions are smooth or turbulent. A southwest wind tends to be more stable and is characterized by increasing speed from the bottom to the top of the rotor blades. By contrast, a north or northwest wind is more likely to be unstable but comes with “a relatively uniform speed across the turbine rotor.”

Archer cautioned that the results are specific to the Cape Cod area, and that more research is necessary to determine whether similar atmospheric conditions exist in other offshore environments, such as New Jersey, Maryland or other parts of Massachusetts.

“It’s important to ensure that science doesn’t underestimate the possible wind resources,” she said. “Now that we know what is happening in Cape Cod, we have more work to do to determine whether it exists anywhere else or whether it is unique to this region.”

Reporter Gabriel Dunsmith contributed.