How can one significantly reduce the winds of nature’s most destructive storms, and at the same time provide up to half of the world’s electric power? The answer, according to Dr. Mark Jacobson of Stanford’s Civil and Environmental Engineering department, is to install massive arrays of tens of thousands of offshore wind turbines, which can extract wind energy from hurricanes and dramatically reduce their winds and storm surges. I’m in San Francisco this week for the annual meeting of the American Geophysical Union (AGU), the world’s largest climate science conference, where Dr. Jacobson presented a talk titled, “Taming hurricanes with arrays of offshore wind turbines that simultaneously reduce global warming and air pollution and provide normal electric power.” Using a 3-D global atmospheric computer model with finer-scale meshes zoomed in along the U.S. coast, he ran simulations of Hurricane Katrina and Hurricane Sandy, and studied how an array of 70,000 wind turbines that generate 300 Gigawatts of power placed along the coast might impact these storms. The simulations showed that as the outer winds of these hurricanes moved over the wind turbines, they extracted enough energy from the storms to reduce the winds by 50%, and increase the central pressure by 16 mb. A decrease in the storm surge of 6 - 72% occurred as a result.
Figure 1. The wind speeds at 15 meters above the surface as simulated at 10 am EDT August 29, 2005 during Hurricane Katrina. Left: Katrina’s winds without an off-shore wind turbine array of 70,000 units present (7.58-MW Enercon E-126 turbines spaced every 0.45 km2 within 100 km of the coast.) Right: Hurricane Katrina after passing through the simulated array. The wind turbines extracted a huge amount of energy from the hurricane, significantly reducing its winds. Image credit: Mark Jacobson and Cristina Archer, “Taming Hurricanes With Arrays of Offshore Wind Turbines”, presentation made to the Willet Kempton Wind Energy Symposium University of Delaware February 27, 2013.
Vulnerability of wind turbines to hurricane winds
The wind turbines used in the study shut down when winds hit 76 mph, and are destroyed at wind speeds of 112 mph. The eyewall winds of Katrina did destroy a number of turbines in the simulation. Even so, the cost of the lost turbines in such a case would likely be made up for by the reduced damage of the hurricane’s winds and storm surge at the coast due to the presence of the wind turbine array. Note that a 2012 paper by Rose et al. that got a lot of media attention, “Quantifying the hurricane risk to offshore wind turbines“, significantly overestimated the risks of wind turbines being destroyed by a hurricane, as pointed out by NOAA hurricane scientist Dr. Mark Powell, and as conceded by the authors of the study. It is reasonable to build large offshore arrays of wind turbines in hurricane-prone regions, provided some extra engineering effort is put into the design of these turbines. A talk presented at AGU yesterday by Jay Apt and Stephen Rose of Carnegie Mellon University, “Quantifying the hurricane risk to offshore wind power,” recommended that offshore wind turbines install backup power systems in order to orient the blades correctly to reduce extreme wind loads during hurricane conditions.
More research needs to be done on how large wind turbine arrays might affect the weather. These turbines could potentially cause significant changes to precipitation patterns along the coast. As I blogged about in 2012, in the Southeast U.S., tropical cyclones provide 15 - 20% of the annual precipitation, and 20% - 50% of all droughts between 1960 - 2009 were busted by a landfalling tropical storm or hurricane. If wind turbine arrays reduce the intensity of tropical storms making landfall, it makes sense that the amount of rain they dump will also decline. Droughts are often more damaging than hurricanes, and it may be necessary to shut down a large array of coastal wind turbines in a situation where a tropical storm or hurricane with drought-busting rains is headed for a drought region. Who should make this decision? How strong of a storm should we let hit? There are many tough questions to answer.
Figure 2. Wind turbine damage on Miyakojima Island, Japan after Typhoon Maemi struck on September 11, 2003. Image credit: Takahara, et al., 2004, “Damages of wind turbine on Miyakojima Island by Typhoon Maemi in 2003.”
Wind to power the world?
Dr. Jacobson is a big booster of wind power. A 2012 paper that he published along with co-author Christina Archer in Proceedings of the National Academy of Sciences (PNAS) found that there is enough wind to exceed the total world energy demand by several times, even after accounting for reductions in wind speed caused by the wind turbines. Their model showed that 4 million turbines, each operating at a height of 100 meters and producing 5 megawatts, could supply 7.5 terawatts of power—more than half the world's all-purpose power demand—without significant negative effects on the climate. "To get there, however, we have a long way to go. Today, we have installed a little over 1 percent of the wind power needed," Jacobson said, in a Stanford press release. Half of the 4 million turbines would be situated over water, and the other 2 million would require a little more than 0.5% percent of Earth's land surface—about half the area of the state of Alaska. However, virtually none of this area would be used solely for wind, but could serve dual purposes such as open space, farmland, ranchland or wildlife preserve.
Have a great weekend, everyone, and I’ll be back Monday with a new post.