Politics aside, most energy experts agree that cheap,
clean, renewable wind energy holds great potential to help the world satisfy
energy needs while reducing harmful greenhouse gases. Wind farms placed
offshore could play a large role in meeting such challenges, and yet no
offshore wind farms exist today in the United States.
In a study published in Geophysical
Research Letters, a team of engineers at Stanford University
has harnessed a sophisticated weather model to recommend optimal placement of
four interconnected wind farms off the coast of the Eastern
United States, a region that accounts for 34% of the nation’s electrical
demand and 35% of carbon dioxide emissions.
“It is the first time anyone has used high-resolution
meteorological data to plan the placement of offshore wind grid,” said senior
author Mark Z. Jacobson, a professor of civil and environmental engineering. “And this sophistication has provided a deeper level of understanding to the
Beginning with 12 energetic potential locations, the
engineers winnowed down the sites to four optimal sites. Total maximum capacity
of the interconnected grid is 2,000 MW, roughly equivalent to the yearly
capacity of one-and-a-half conventional coal-fired power plants. Each farm
would have approximately 100 turbines, delivering an individual maximum capacity
of 500 MW.
“Two thousand megawatts and four farms are somewhat
arbitrary figures. The sizes and locations could be adjusted for economic,
environmental, and policy considerations,” said Jacobson.
“An offshore grid as an extension
of the onshore grid in this region will improve reliability, while reducing
congestion and energy price differences between areas,” said Mike
Dvorak, the lead author of
the study and a recent PhD graduate in civil and environmental engineering at
The optimized grid was located in the waters from Long
Island, New York to Georges Bank,
a shallows about a hundred miles to the east of Cape Cod.
The near-shore locations take advantage of consistent sea breezes that occur
naturally due to the daily difference in temperature between land and sea. The
offshore farms experience stronger, though less regular, frontal storm
activity. The four farms would be interconnected to help balance output across
“Until recently, large scale wind resource assessments
have neglected the aspect of time. We matched peak productivity with peak
demand at specific times of day and year,” said Dvorak. “Our analysis matches
production to demand.”
Wind farms on land, for instance, tend to see daily peak
output at night, when demand is lower. Seasonally speaking, demand usually
spikes in the late afternoons of summer when air conditioning needs are high,
but this time of year is also known for a dearth of storms and a meteorological
phenomenon known as the Bermuda High, a high-pressure center that affects winds
along the entire coast.
“In some areas, like Massachusetts, the
Bermuda High boosts sea breezes,” said Dvorak. “But south of Long Island, N.Y.,
where one offshore grid has been proposed, the Bermuda High has the opposite
effect and often hinders sea breezes.”
The near-shore locations take advantage of consistent sea breezes that occur naturally due to the daily difference in temperature between land and sea. Image: Sergiy Serdyuk
Balance of power
Beyond matching production and demand cycles, the researchers had to balance
several technical challenges in their models.
“The farms had to be in waters less than 50 m deep to
allow use of bottom-mounted turbines and near urban load centers like Boston and New
York,” said Jacobson. “And, we wanted to smooth power
output, ease hourly ramp rates and reduce hours of zero power.”
The engineers took a novel approach, choosing to
interconnect the offshore farms. Offshore wind farms in other parts of the
world today are connected individually to the onshore grids.
“The goal is to even out the peaks and valleys in
production,” said Dvorak. “In our model, expensive no-power events—moments when
individual winds farms are producing zero electricity—were reduced by more than
half from nine percent to four by connecting the farms together.”
In the final analysis, the interconnected grid was able
to yield a year-long capacity factor of over 48%, meaning that the grid could
reliably produce close to 1,000 MW on average over the course of a year.
“Generally, with wind farms,
anything over 35% average capacity is considered excellent,” said Jacobson.
Among its findings, the Stanford model recommended a farm
in Nantucket Sound, precisely where the controversial Cape Wind
farm has been proposed. The Cape Wind site is contentious because, opponents say, the
tall turbines would diminish Nantucket’s
considerable visual appeal.
By that same token, the meteorological model puts two
sites on Georges Bank, a shallows located a
hundred miles offshore, far from view in an area once better known for its
prodigious quantities of cod. The fourth site is off central Long
The researchers last looked at the economics of
installing their offshore grid, which they said would have the advantage of
sharing costs across several states, potentially increasing political support
for the plan.
“This paper should be seen as a
tool for energy planners to better inform their renewable energy decisions
across a densely populated area,” said Jacobson. “It is an opportunity to
collaborate on a shared system that reduces costs while benefitting a large and
important center of electrical demand in the U.S.”