Researchers claim vast offshore wind farms could calm hurricanes

Source: Elizabeth Harball, E&E reporter • Posted: Thursday, February 27, 2014

It’s physics 101: A wind turbine spins by extracting energy from moving air. As a turbine moves faster, the wind powering the twirling blades slows down a little bit.But what happens when turbines are hit with the high-speed winds that power hurricanes like Sandy or Katrina? Could an offshore wind farm actually dampen the destructive force of a superstorm?Given a great many turbines, the answer is yes, according to new research. For their study published today in the journal Nature Climate Change, the authors used computer models to show that gargantuan offshore arrays upstream of cities or along coastlines could slash hurricane wind speeds by up to 92 mph and reduce storm surges by between 6 and 79 percent.Furthermore, the study claims that given the energy produced, hurricane losses prevented and other pluses inherent to renewable energy, an offshore wind array could be cheaper than the sea wall projects taken on by cities like New York and New Orleans as they prepare for the stronger storm surges predicted to come with climate change. “Offshore wind would be useful in any case for generating electricity, but this also shows there would be an additional benefit of reducing hurricane risk,” said Mark Jacobson, lead author of the study and professor of civil and environmental engineering at Stanford University. According to Jacobson and co-author Cristina Archer, associate professor at the University of Delaware’s College of Earth, Ocean and Environment, because the offshore turbines would see the slower winds at the hurricane’s outside rim first, an offshore array could also save itself from some degree of damage. “The turbines have already started to take all the kinetic energy away from the outskirts of the hurricane, so you can imagine that now there are all these bands of weaker winds that are feeding into the hurricane,” Archer explained. “… For every turbine that stands up, the next turbine experiences less wind.”

Only a ‘thought experiment’?

It’s important to note that by “large turbine arrays,” the authors mean very large turbine arrays, on the order of more than 300 gigawatts and hundreds of thousands of turbines, in most cases. Offshore arrays operating today generally have a capacity of several hundred megawatts coming from, at most, close to 200 turbines — and none of these farms exists off U.S. shores. One scenario in Jacobson’s study modeled for a farm spanning the Gulf of Mexico from Florida to Texas. “These arrays that we looked at could generate enough electricity to power the country, basically — actually, two or three countries,” Archer said. But Archer argued that she and her co-authors found that smaller wind farms — farms half or even a 10th of the size modeled for in the paper — could also dampen hurricanes. “We started off with large arrays because we wanted to make sure that we saw an impact,” Archer said, “but we also looked at the sensitivity of the results to reducing the number of turbines, so we cut them in half, cut them to about a 10th, and we still saw an effect. Obviously, the effect was less, but it wasn’t 10 times less.” But Somnath Baidya Roy, an associate professor at the Indian Institute of Technology’s Centre for Atmospheric Sciences in New Delhi, called the study a “thought experiment,” saying today’s offshore arrays wouldn’t make much of a dent in a superstorm like Sandy. “What we call large wind farms by today’s standards are actually relatively small, so these kinds of wind farms are not going to have the effect that we see in this study,” said Baidya Roy, who was not involved in the study. “It is obviously very interesting scientifically speaking … but you cannot just take this study to the bank tomorrow and ask for loans and start building these wind farms. We have a long way to go to get to that point.” The study didn’t consider other environmental impacts, such as how such huge development projects might stress the ecology of sensitive coastal areas, Baidya Roy said. He was also uncertain about the study’s claim that offshore wind arrays would be cheaper than sea walls. “There are so many unknowns in terms of the market of energy,” he said. “I am not an economist, but it seems that significant government intervention in the form of subsidies and tax breaks will be required to make large wind farms economically feasible.” However, Baidya Roy said this wasn’t a reason to disregard the paper’s findings. “I know that a lot of people would look at this and the scale of the wind turbines and the wind farms and say, ‘Oh, this is too big.’ Just that should not be a reason to dismiss this study. These kinds of large technological solutions are something that we need if we want to combat climate change.”

Other climate impacts to consider

An additional question remains: If such huge offshore wind farms can slow hurricanes, what about their impact on other aspects of weather and climate? Archer said she and the paper’s other authors weren’t worried about this. “The effect on the global circulation of the global climate is very negligible,” she said, referencing a 2011 paper she co-authored with Jacobson. “With a hurricane, the challenge is a different one — it’s a different beast. It’s very powerful, and yet it’s somewhat localized.” But David Keith, a professor of applied physics at Harvard University, is not so quick to dismiss the question. In a 2012 paper in Environmental Research Letters, Keith challenged Archer and Jacobson’s claim that the massive deployment of wind farms — that is, hundreds of terawatts of wind power — would not have a significant influence on both global wind speeds and temperatures. Keith stressed that the short-term impacts of massive offshore wind farms on both wind speeds and temperature were probably preferable to the long-term impacts of the continued use of coal plants. But he believes Archer and Jacobson are wrong to say such large offshore wind farms would dampen hurricanes but not influence the global climate in other important ways. “If you look at coal versus wind for 1,000 years, wind is infinitely better than coal,” Keith said. “If you look at coal versus wind for 50 years, it’s not so simple.”