Massive arrays of offshore wind farms could significantly reduce the speed of winds and the height of waves during hurricanes, according to a new study. Wikimedia Commons/Mariusz Paździora
A computer simulation has shown that enormous offshore wind arrays can temper the wind speeds and wave heights of hurricanes.
March 25, 2014—Researchers from Stanford University and the University of Delaware have hit upon yet another benefit of offshore wind farms: not only do wind farms offer clean energy, but according to a paper published online last month in Nature Climate Change, such arrays can also reduce wind speeds and wave heights during hurricanes. Had such offshore wind farms existed near the city of New Orleans when Hurricane Katrina struck in 2005 and Hurricane Isaac hit in 2012, or near the East Coast of the United States when Hurricane Sandy struck in 2012, the impact of the storms on coastal cities and infrastructure could have been significantly decreased.
The computer simulation models were developed by Mark Z. Jacobson, Ph.D., a professor of civil and environmental engineering at Stanford University, and Cristina Archer, Ph.D., an associate professor, and Willett Kempton, Ph.D., a professor, both in the College of Earth, Ocean, and Environment at the University of Delaware.
The genesis of the idea for the computer simulation came from the impact that Hurricane Sandy had on New York State, according to Jacobson, who wrote in response to questions posed by Civil Engineering online. “I was developing a plan for New York State to change its energy infrastructure for all purposes to wind, water, and sunlight—this plan required lots of offshore wind,” Jacobson said. “When Hurricane Sandy hit, a question arose as to whether the hurricane would destroy the offshore wind turbines we proposed, [so] I decided to study that issue.”
The resulting paper, “Taming Hurricanes with Arrays of Offshore Wind Turbines,” is the first study to examine the issue of wind turbine impacts on hurricanes, Jacobson noted.
“With a large array of offshore turbines, it was possible to extract enough energy from the hurricane to prevent up to 80 percent [of the] storm surge and reduce wind speeds by more than 50 percent,” Jacobson said. Rather than being damaged by hurricane force winds, the turbines in large offshore wind arrays actually slow down the outer rotation winds of a hurricane, according to Jacobson. In turn, this slowing of outer wind speeds decreases the wave heights of the storm, which in turn reduces the movement of air toward the center of the hurricane. This reduced movement increases the central pressure of the storm, which slows the winds of the entire hurricane, causing it to dissipate more quickly.
The simulation modeled three hurricanes: Hurricane Katrina in 2005 and Hurricane Isaac in 2012, both of which impacted Louisiana, and Hurricane Sandy in 2012, which impacted the East Coast of the United States and the coastlines of New York and New Jersey states in particular. “[We] selected the number of turbines based on how many would fit in a specified area, [but] we also ran sensitivity tests with half the number of turbines and found a significant benefit even with half the numbers,” Jacobson said.
The simulations used enormous arrays, all of which would include turbines located no more than 100 km from shore. In one Katrina simulation in which 78,000 wind turbines were placed off the coast of New Orleans, wind speeds were decreased between 80 and 98 mph (36-44 meters per second), and the storm surge decreased by up to 79 percent.
An offshore wind array of 414,030 turbines placed along much of the East Coast, from North Carolina to Vermont, for a Hurricane Sandy simulation resulted in a projected a wind speed reduction of between 78 and 87 mph (a decrease of 35 to 39 m per second) and as much as a 34 percent decrease in storm surge. A smaller array including 112,014 turbines placed between Washington, D.C. and New York City still resulted in a wind speed decrease of approximately 80 mph, or 36 m per second, and a storm surge reduction of between 12 and 21 percent.
Other methods of protecting coastlines from hurricanes exist, such as the U.S. Army Corps of Engineers’ Inner Harbor Navigation Canal Surge Barrier, which was named the winner of ASCE’s 2014 Outstanding Civil Engineering Achievement (OCEA) Award on March 20. However, while enormous sea walls can protect coastal regions from storm surges, such barriers have only one function: prohibiting water from reaching shorelines. Enormous wind turbine arrays would have three. Not only would they protect against hurricanes, mitigating both storm surge levels and wind speeds, they would also be actively generating electricity year round. And existing turbine technology can already withstand wind speeds of up to 112 mph, the range of a category 2 to 3 hurricane, according to Jacobson.
The scale of the offshore wind farms simulated in the paper dwarfs any currently in existence: when the London Array became fully operational last year as the largest offshore wind farm on the globe, it did so with a mere 175 turbines located 20 km off the southeastern coast of the United Kingdom. (Read “Largest Offshore Wind Farm Powers Up near London,” on Civil Engineering online.) But by installing offshore wind arrays, of any size, “the turbines would be installed based on their ability to generate electric power so would pay for themselves over 30 years from electricity sales,” Jacobson pointed out. Not only would the arrays pay for themselves over time, “the additional cost of hurricane mitigation is zero,” he notes.
The turbines in such arrays would not only offset fossil fuel use, they could also stabilize electricity costs because the fuel cost of wind is zero, according to Jacobson. A video simulates the results for Hurricane Katrina.