America’s first offshore wind farm might have to brace for turbulence

The first offshore wind farm off Rhode Island is finally complete and will be switched on in October. While the farm is small, it’s a big step for offshore wind in America, which has massive potential of about 4,200 gigawatts of offshore wind, according to the National Renewable Energy Laboratory. That could make a huge dent in the nation’s carbon emissions. But it might not be so easy to tap into.

A new study suggests that it will take a lot of thought and planning, and could likely be expensive. The study found that winds off the Northeastern shore may be more powerful—but also much more turbulent—than expected.

The findings could color the design of future offshore wind farms. They could help wind farm developers to assess how much power can be produced at a site, what type of turbines to use, how many to install, and how to place them.

Off-coast wind and turbulence measurements until now have been based on data from buoys that is then extrapolated to estimate the corresponding conditions at the height of a turbine rotor blade.

Researchers at the University of Delaware and Stony Brook University took a more direct approach. They analyzed wind data taken between 2003 and 2011 at the Cape Wind Tower located off the coast of Martha’s Vineyard, Massachusetts. The tower has sensors located at 65 feet, 131 feet, and 196 feet. In the summers of 2013 and 2014, they flew airplanes above and around the tower 19 times, measuring wind, temperature, and humidity during different weather conditions. Then they combined all of these measurements with buoy data.

Their findings, published in the Journal of Geophysical Research: Atmospheres, are that atmospheric conditions around Cape Wind are unstable, leading to turbulent winds 40–80 percent of the time depending on season and day. The advantage of these turbulent conditions is “extra wind power, but that extra wind power comes at a cost: the cost of more stress on the turbine’s blades,” said lead researcher Christina Archer in a press release.

By contrast, studies of European offshore winds show that atmospheric conditions in the Baltic Sea and the North Sea are stable 80 percent of the time, giving relatively smooth, calm winds. Europe already has a gigantic lead over the US in offshore wind power with around 10 gigawatts of installed offshore wind capacity.

The research team says they will need to do similar studies along the entire East Coast since offshore wind installations are planned for Maryland, New Jersey, and Massachusetts. —Prachi Patel | 25 August 2016

Source: Archer CL et al. On the predominance of unstable atmospheric conditions in the marine boundary layer offshore of the U.S. northeastern coast. Journal of Geophysical Research: Atmospheres. 2016.

Photo: Vattenfall/flickr

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