University of Delaware  [Printer-friendly version]
February 1, 2007


By Tracey Bryant

The wind resource 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 percent
increase in future energy demand -- according to a study by
researchers at the University of Delaware and Stanford University.

Willett Kempton, Richard Garvine and Amardeep Dhanju at the University
of Delaware and Mark Jacobson and Cristina Archer at Stanford, found
that the wind over the Middle Atlantic Bight, the aquatic region from
Cape Cod, Mass., to Cape Hatteras, N.C., could produce 330 gigawatts
(GW) of average electrical power if thousands of wind turbines were
installed off the coast.

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

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

The study marks the first empirical analysis in the United States of a
large-scale region's potential offshore wind-energy supply using a
model that links geophysics with wind-electric technology--and that
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.

The results are published in the Jan. 24 issue of Geophysical Research
Letters, a peer-reviewed scientific journal produced by the American
Geophysical Union, a nonprofit organization of geophysicists with more
than 49,000 members in 140 countries.

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, including a survey of Cape Cod residents,
who largely have opposed a major wind farm proposed for their coastal
area, and a more recent survey in Delaware that revealed strong
support for offshore wind power as the next electricity source for the

"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 recently completed her doctorate, and Dhanju, who is
working on his doctorate, also carried out parts of the research.

The Delaware Green Energy Fund, UD's College of Marine and Earth
Studies, the Delaware Sea Grant College Program and the Global Climate
and Energy Project at Stanford supported the study.

Estimating the wind power resource

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 3,000 meters (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 80 meters (262 feet) tall, with blades as long as 55 meters (180

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 be
erected 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.

Anemometer readings from the nine NOAA weather buoys in the Middle
Atlantic Bight were analyzed. To determine the average wind over the
region, the scientists reviewed all the wind-speed data from the past
21 years from one of the buoys. The findings were then extrapolated to
the height of the offshore wind turbines currently being manufactured
in order to determine the average power output per unit. At the
current 80-meter (262-foot) wind turbine height, the extrapolated wind
speed of the mid-range buoy is 8.2 meters 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 located at varying
distances from shore, out to 100 meters of water depth, over an ocean
area spanning more than 50,000 square miles, from Cape Cod to Cape

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--the researchers
found that the shelf's reported energy sources would amount to only
one-tenth of the wind resource and would be exhausted in 20 years.

Addressing wind power fluctuations and energy priorities

While 330 gigawatts is the average output of the entire offshore wind
resource over the Mid-Atlantic Bight, the researchers note that
offshore wind is not uniform and offer suggestions for addressing
power fluctuations.

"Over a large area like this, the wind blows stronger at some times
and places, weaker at others," Kempton said.

To make wind power more uniform, the study shows that multiple sites
could be connected through power lines to reduce the number of times
of both maximum and minimum power. Changes in new and replacement
energy-using devices, including automobiles, also could provide for
greater power storage.

"Battery and plug-in hybrid automobiles, for example, have large
storage that is unused when the car is parked," Kempton said.

With a scientifically reliable estimate of the region's offshore wind
power potential now in hand, how likely are we to actually install
more than 100,000 wind turbines off the Mid-Atlantic coast?

Nysted wind farm in the Baltic Sea off Denmark. Photo by Jeremy
Firestone Kempton said it's a matter of priority. "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." On the
practicality of producing 166,720 wind turbines, co-author Richard
Garvine noted, "the United States began producing 2,000 warplanes per
year in 1939 for World War II, increased production each year, and, by
1946, had sent 257,000 aircraft into service.

"We did that in seven years, using 1940s technology," he said.

More information on wind power is available from UD's Offshore Wind
Power Group at