4-2 Taking the Power out of Wind

Offshore Wind Farms Could Knock Down Hurricanes

Hurricanes are unstoppable, right? Apparently not. An intriguing new computer simulation shows that 78,000 large wind turbines spread across 35,000 square kilometers of ocean outside of New Orleans would have cut Hurricane Katrina’s category 3 winds at landfall by 129 to 158 kilometers per hour (80 to 98 miles per hour) and reduced the storm surge by 79 percent. The same collection of turbines offshore of New York City would have dropped Hurricane Sandy’s winds by 125 to 140 kph and the surge by up to 34 percent.

That sounds impressive. But wait…78,000 turbines? Each one 100 meters high with a blade span 127 meters in diameter spaced about 650 meters apart and spanning a region of ocean 2.5 times the size of Connecticut? The idea sounds crazy, except for the bottom line: “The cost would be zero,” says Mark Jacobson, a professor of civil and environmental engineering at Stanford University. “The turbines pay for themselves through the revenue from generating electricity. The storm surge and wind protection are free—a bonus.”

Actually the cost to erect such a massive wind farm, or set of farms, would be many billions of dollars. But Jacobson says the cost would be recouped over time through electricity sales, replacing many coal-fired or nuclear power plants. And then there is the alternative, he notes: “New York is considering building $20 billion in seawalls” to prevent future storm surge damage after Hurricane Sandy caused more than $60 billion in losses in New York and New Jersey. “Seawalls don’t pay for themselves,” Jacobson says. “Turbines do.”

Jacobson has calculated in mind-bending detail how turbines could defuse hurricane forces, all laid out in a new paper appearing in Nature Climate Change. The exercise, based on computer simulations, is the latest step in a series of grand plans the engineer has been building for renewable energy technologies.

In 2009 Jacobson and Mark Delucchi, a research scientist at the University of California, presented a roadmap for powering the entire world with wind, water and solar technologies. Last year Jacobson and his colleagues unveiled a detailed plan for powering all of New York State in the same way, having already completed the process for California. Tens of thousands of offshore wind turbines are a central part of each plan. “Offshore winds are pretty continuous,” Jacobson says. “They’re not intermittent,” which is the knock against wind power—that no electricity is generated when the wind doesn’t blow.

But wouldn’t turbines snap or topple over in hurricane winds? No, because of how the farms would reduce the wind energy. Here’s how it would work: As the outer bands of a hurricane approach the massive set of wind farms, the turbines spin, taking energy out of the winds. Those winds usually whip up waves and pull air up alongside the hurricane eye wall, increasing the storm’s strength. If the outer-band winds are diminished, the storm’s power decreases; wind speeds slow and the surge lessens. As the hurricane continues to cross the wind farms, the turbines continue cutting down the energy, so the hurricane loses strength as it advances. Very high winds never build to strike the turbines.

That scenario sounds good until different permutations are considered, but Jacobson has an answer for each one. What if the winds strike the farms at, say, a 45-degree angle instead of head-on? The turbines still reduce the energy, he says. What if the hurricane is, say, 50 kilometers to the east or west of the wind farms? The turbines would only reduce the fringes of the storm but the storm would not be on a track to damage a major city behind the wind farms.

Jacobson acknowledges that turbines could still be damaged by a ferocious storm. Today operators shut off and lock down turbines when winds reach about 125 kph (78 mph). Once winds surpass 180 kph (120 mph), the borderline between a category 2 and category 3 hurricane, turbines will likely sustain damage. Although Jacobson says the power dissipation of the wind farms should keep winds below those levels, engineers at places such as the National Renewable Energy Laboratory are studying how to strengthen turbine towers and blades.

When speaking about the hurricane study, Jacobson made a point to note that “I’m not focused just on wind. We need solar, wind, water power, geothermal…. But wind is already happening. It provides 4.5 percent of the electricity in the U.S. I’m looking at what’s the best solution to energy demand, health impacts and climate. I’m not advocating anything. It’s just the science. If coal were the cleanest choice, I’d be pushing coal. But it’s not.”

It will be interesting to see the media and public reaction to the hurricane study. One great objection is that wind turbines can kill a lot of birds. Jacobson even has a scientific response for that. A major study by Benjamin Sovacool of the Center on Asia and Globalization found that wind farms cause 0.3 to 0.4 avian fatality per gigawatt-hour of electricity generated. Fossil-fueled plants cause 5.2 fatalities per gigawatt-hour, including the effects of mining, habitat destruction, acid rain, mercury poisoning and climate change. “Fossil-fuel electricity,” Jacobson concludes, “kills 10 times as many birds per kilowatt-hour than wind does.”

Jacobson seems to have a dispassionate answer for everything. Still, 78,000 turbines?