February 13, 2012
Texas, U.S.

Study: Offshore wind farms at risk from hurricanes

By Mark Collette, Corpus Christi Caller-Times, www.caller.com 13 February 2012

CORPUS CHRISTI – In the worst case, nearly half the turbines in proposed offshore wind farms along the most vulnerable parts of the Gulf and Atlantic coasts are likely to be destroyed by hurricanes in a 20-year period, a new study suggests.

The study from Carnegie Mellon University says strategies should be considered to protect the reliability of the nation’s electricity grid and reduce risks to wind farm operators before large-scale offshore wind development advances in the United States.

Mitigation could include choosing different sites or paying more to increase the strength and maneuverability of turbines, study co-author Paulina Jaramillo said.

Compared with the East Coast, the Gulf Coast has more high-intensity hurricanes that cause the most damage. But it also has better offshore wind resources. In South Texas, Baryonyx Corp. has been awarded leases totaling 67,500 acres off Mustang Island and South Padre Island. No turbines have been built.

The study, published today in the Proceedings of the National Academy of Sciences, used data from three sites on the Eastern Seaboard and an area off Galveston County, with the latter being the most susceptible to hurricane damage, researchers concluded. A 50-turbine wind farm in Galveston County would likely lose 16 turbines in 20 years, they found.

A group of developers called Wind Energy Systems Technology has a lease for 11,355 acres about seven miles off the coast of Galveston.

Offshore projects in the United States are part of the U.S. Department of Energy’s calculation that more than 50 gigawatts of electricity must come from offshore turbines if the country is to meet its goal of generating 20 percent of its electricity from wind power. A gigawatt powers roughly 300,000 homes.

Developers favor offshore winds because they tend to be more reliable and blow when electricity demand is highest.

A main concern, the researchers found, is how a grid that is more dependent on wind power would be affected if wind towers buckle in a storm. They hypothesized that generation reserves can be brought online to cover for wind plants shut down after a storm.

The study’s worst-case projections assume that turbines can’t yaw, or change direction, under hurricane conditions to reduce stress on the structure. The authors said the assumption is realistic because turbines typically don’t have backup power for yaw motors and hurricanes may cause widespread power outages. And they said wind may change direction in a hurricane faster than the motors can yaw.

The paper said turbines are designed based on standards for northern Europe that specify maximum sustained wind speeds of about 115 mph. Category 3 hurricanes exceed 111 mph, and the strongest category 5 storms exceed 156 mph.

Most damage is likely to come from Category 4 and 5 storms, the study found. In 2003, a wind farm of seven turbines in Japan was destroyed by a Category 4 typhoon with sustained winds of 138 mph.

Mark Leyland, senior vice president of offshore wind projects for Baryonyx, had not read the study but said that while the strongest hurricanes may damage turbines, it doesn’t necessarily mean all should be built to withstand 156 mph.

“Do you design for that? I don’t know,” he said. “Between Corpus Christi and Brownsville, we’ve only had about three Category 5 storms in the last 100 years.”

He noted a December event in the United Kingdom in which gales up to 165 mph destroyed some onshore turbines in Scotland but left most undamaged.

“There’s an insurance market in the Gulf of Mexico that understands the risk of hurricanes and is prepared to insure for that risk,” Leyland said. “And then you have to mitigate that risk as best you can.”