Hurricane Earl poses question about East Coast offshore wind farms

Hurricane Earl heads for the East Coast, pictured here with Hurricane Danielle to the north (photo: NASA)

Hurricane Earl is moving up the East Coast today, forecast to reach Massachusetts waters by midnight.

The storm has lost some of its power since traveling up to North Carolina, but is still expected to lash islands like Nantucket and Martha’s Vineyard with winds of 100 miles an hour.

With developers drawing up plans to locate offshore wind farms along the East Coast, the hurricane poses a question as to whether turbines can withstand hurricane force winds.

So far, the world’s offshore wind turbines are located in Europe, in the Baltic, the North Sea and the Irish Sea, where there are no hurricanes.

Though there are some in the industry that say the technology has been proven well enough to skip over demonstration projects in North America, the conditions here are unlike anywhere where offshore wind turbines have been installed before.

Hurricane Earl shows why demonstration projects are needed here, expensive as they may be.

Though offshore wind turbines are designed with stronger winds in mind, and can feather to protect their blades from excessive winds. Siemens‘ 3.6MW turbines, to be used in the Cape Wind project near Nantucket, shut down at 25 meters per second (about 56mph)

Even feathered, the question is how well wind turbine structures cope with wind speeds twice as strong as that cut-out speed.

Rhode Island and Massachusetts are both racing to complete the nation’s first offshore wind farm, with Rhode Island proposing an eight-turbine demonstration project while Massachusetts forges ahead with a 130-turbine project in the form of Cape Wind.

Though engineers will be sure to keep in mind the weather conditions that can occur along the Eastern Seaboard, and Cape Wind Associates suggests its turbines will withstand 150mph winds. The Rhode Island approach might offer less risk in showing off the technology in these conditions, however.

In North Carolina, Duke Energy has canceled a small demonstration project that would have been partially protected by its location in a lagoon. It said economically it makes more sense to go straight to the construction of a large-scale wind farm out in the Atlantic. But, the hurricane risks do increase the further south you go.

Bluewater Wind, which is seeking to develop offshore wind projects off Delaware, Maryland, New Jersey and New York, states that:

Modern wind turbines are engineered to withstand the stress of extremely high winds and will remain standing, even in a hurricane-force storm. In the most extreme winds, sophisticated microprocessors automatically stop the turbine and position the blades so that they can safely ride out the storm. Once the strongest winds have passed, the wind park resumes operation.

However, assurances from manufacturers still need to be tested out in the field. Onshore wind farms around the Gulf of Mexico can given an idea of how towers and blades can withstand prolonged wind forces, but offshore wind turbines offer a different set of construction and design characteristics, including different foundation systems.

Talk of deepwater or floating wind turbines will also offer a whole new ball game in major storms. There are still some interesting studies to be done in this area, including research currently being carried out by the Worcester Polytechnic Institute in Massachusetts.