Offshore wind turbines need adjustments to survive Category 5 hurricanes
Offshore wind turbines are growing in size, strength and power output, but new research from National Center for Atmospheric Research in Boulder, Colorado and the U.S. Department of Energy's National Renewable Energy Laboratory in Golden, Colorado tells us that while these improvements are amazing, there are still more to be made.
As wind farms start to be approved and finally constructed along the Atlantic coast of the U.S., one of nature's most powerful occurrences must be considered: hurricanes. Current turbines are strong enough to withstand them, but the study found that the strongest hurricanes, Category 5, would likely be more than the turbines could take.
In those hurricanes, wind speeds reach up to 90 meters per second.
"Wind speeds of this magnitude have been observed in hurricanes before, but in only a few cases, and these observations are often questioned because of the hazardous conditions and limitations of instruments," said George Bryan of NCAR. "By using large-eddy simulations, we are able to show how such winds can develop and where they occur within hurricanes."
The other thing to consider is the veer of the wind in these hurricanes, or the change in wind direction across a vertical span. In a Category 5 hurricane, the wind can change direction by as much as 55 degrees between the rotor and hub of a wind turbine, meaning an overwhelming strain on the blades.
The Atlantic coast is threatened by hurricanes each year, and while the strongest of hurricanes are not common, they happen with enough frequency that wind farms will need to be built with those threats in mind.
"Success could mean either building turbines that can survive these extreme conditions, or by understanding the overall risk so that risks can be mitigated, perhaps with financial instruments like insurance," said Professor Julie Lundquist of ATOC and CU Boulder's Renewable and Sustainable Energy Institute (RASEI). "The next stage of this work would be to assess how often these extreme winds would impact an offshore wind farm on the Atlantic coast over the 20-to-30-year lifetime of a typical wind farm."
The U.S. finally has its first wind farm at Block Island, Rhode Island and the potential for wind energy generation along the east coast is great. It will be a necessary part of the country's transition to cleaner energy, so studies like this will hopefully guide engineers and planners to build turbines and wind farms can take whatever nature throws at them, or at least plan for the costs when they can't.