8 February 2007

Mid-Atlantic winds could power East Coast

Winds off the Mid-Atlantic coast could supply the energy needs of nine states from Massachusetts to North Carolina, plus the District of Columbia, with enough left over to support a 50% increase in future energy demand, according to a study by researchers at the University of Delaware and Stanford University.

The wind over the Middle Atlantic Bight, the region from Cape Cod, Mass., to Cape Hatteras, N.C., could produce 330 gigawatts of average electrical power if companies installed thousands of wind turbines off the coast, according to the study by Willett Kempton, Richard Garvine, and Amardeep Dhanju at the University of Delaware and Mark Jacobson and Cristina Archer at Stanford.

The estimated power supply from offshore wind substantially exceeds the region’s current energy use, which the scientists estimate at 185 gigawatts, from electricity, gasoline, fuel oil, and natural gas sources.

Supplying the region’s energy needs with offshore wind power would reduce carbon dioxide emissions by 68% and reduce greenhouse gases by 57%, according to the study.

The study marks the first empirical analysis in the U.S. of a large-scale region’s potential offshore wind-energy supply using a model that links geophysics with wind-electric technology. It also defines where wind turbines at sea may be located in relation to water depth, geology, and “exclusion zones” for bird flyways, shipping lanes, and other uses.

Kempton, the UD professor of marine policy who led the study, has worked on several public opinion surveys about offshore wind power over the past three years. One study included Cape Cod residents who largely have opposed a major wind farm proposed for their coastal area; a more recent survey in Delaware revealed strong support for offshore wind power as the next electricity source for the state.

“In doing our surveys and watching the public debate, we saw that no one had solid empirical data on the actual size of the offshore wind resource, and we felt this was important for policy decisions,” Kempton said.

Kempton collaborated with an interdisciplinary team of scientists, including Garvine, who is a physical oceanographer and Maxwell P. and Mildred H. Harrington Professor of Marine Studies at UD, and Jacobson, a professor of civil and environmental engineering at Stanford. Archer, who just completed her doctorate, and Dhanju, who is working on his doctorate, also carried out parts of the research.

The scientists began by developing a model of the lowest atmospheric layer over the ocean. Known as the “planetary boundary layer,” it extends vertically from the ocean surface to up to 9,842 feet and is where strong, gusty winds occur due to friction between the atmosphere and the sea surface, solar heating, and other factors. It provides the “fuel” for offshore wind turbines, which may stand up to 262 feet tall, with blades as long as 180 feet.

The scientists examined current wind-turbine technologies to determine the depth of the water and the distance from shore the wind turbines could be located. They also defined “exclusion zones” where wind turbines could not be installed, such as major bird flyways, shipping lanes, chemical disposal sites, military restricted areas, borrow sites where sediments are removed for beach renourishment projects, and “visual space” from major tourist beaches.

To estimate the size of the wind power resource, the researchers needed to figure out the maximum number of wind turbines that could go up and the region’s average wind power. The spacing used between the hypothetical wind turbines was about one-half mile apart. At a closer spacing, Kempton said, upwind turbines will “steal” wind energy from downstream ones.

After analyzing anemometer readings from the nine NOAA weather buoys in the Middle Atlantic Bight, they determined the average wind over the region. The scientists reviewed all the wind-speed data from the past 21 years from one of the buoys. They then extrapolated the findings to the height of the offshore wind turbines currently in use in order to determine the average power output per unit. At the current 262-ft wind turbine height, the extrapolated wind speed of the mid-range buoy is 26.9 feet per second (18.3 miles per hour or 16 knots).

The scientists’ estimate of the full-resource, average wind power output of 330 gigawatts over the Middle Atlantic Bight is based on the installation of 166,720 wind turbines, each generating up to 5 megawatts of power. The wind turbines would be at varying distances from shore, out to 328 feet of water depth, over an ocean area spanning more than 50,000 square miles, from Cape Cod to Cape Hatteras.

In comparison to the oil and natural gas resources of the Atlantic Outer Continental Shelf—the submerged land that lies seaward from 3 miles offshore and is under federal jurisdiction—researchers found the shelf’s reported energy sources would amount to only one-tenth of the wind resource and would be exhausted in 20 years.

“Today, market forces and incremental technology developments will gradually make offshore wind the least-cost power in more and more East Coast locations,” Kempton said. “On the other hand, if climate change becomes a much greater priority for the United States, our study shows how we could displace more than half the carbon dioxide emissions of the Mid-Atlantic area quickly, using existing technology.”

For related information, go to www.isa.org/environment.