CEE studies show new potential in wind energy

Sept. 25, 2012, 3:02 a.m.

Two recent Stanford Civil and Environmental Engineering (CEE) studies have shed light on the vast potential of wind energy to power the East Coast of the United States and the world.

Together, offshore and onshore wind farms could deliver between 80 and 350 terawatts (TW) of energy globally, depending on geographic placement, according to a study by Mark Jacobson, professor of civil and environmental engineering at Stanford, and Cristina Archer, associate professor of geography and physical ocean science and engineering at the University of Delaware. This exceeds the projected global need of 11.5 TW in 2030.

A similar study by Jacobson and Mike Dvorak Ph.D. ‘12 found potential for 965 to 1,372 terawatt-hours of electricity annually from offshore wind farms on the East Coast, enough energy to power the region.

This research differed from previous analyses that were based on wind speeds reported from data stations. The wind speeds were used to estimate the wind power for the turbines to extract; this power was then converted to the potential power generated by the turbine.

Previous studies using estimation placed the potential of global wind energy at 1 TW, significantly lower than the 80 to 350 TW now projected.

“It is a 3-D problem that they were trying to calculate with a 0-D model,” Jacobson said. “It shows the danger of back-of-the-envelope estimates about phenomena.”

For the new studies, Jacobson and his researchers used a weather prediction climate model, which simulates climate, weather and air pollution at the global, regional and local scales.

The model also simulated, rather than estimated, the effect of wind turbines on neighboring wind turbines. Individual wind turbines in wind farms are subject to interference from nearby turbines, as they take wind from each other, depleting available wind and power output.

To simulate the reduction of wind speed and energy, the researchers put wind turbines into the models, extracted the energy, reduced the wind speed by the amount taken from the extracted energy and recalculated the wind speed for the neighboring turbines.

With this new model of accounting for turbine interference, researchers found a greater saturation potential for the world’s wind power. As the amount of turbines and wind farms increases, the potential decreases until adding more turbines yields diminishing returns.

The study for the East Coast was modeled primarily on offshore, rather than onshore, wind farms.

“Because of the high population density, the East Coast is limited [in] how much onshore energy could be generated,” Dvorak said. “Offshore wind farms allow larger wind centers near New York and Boston.”

Offshore wind farms also have the benefit of generating the most wind energy at peak energy usage times, according to Jacobson. Afternoon sea breezes caused by temperature differences between the land and ocean generate energy for the wind turbines. Onshore wind farms, however, can have peak energy generation at day or night depending on meteorology and topography.

Additionally, because most people live near coasts worldwide, offshore wind farms allow for shorter transmission distances, which can be facilitated by underwater cables.

Proposals are underway for construction of wind farms off the East Coast, including the Cape Wind Project in Massachusetts, which will begin construction in the next two years. As for the Bay Area, wind energy has potential, but more logistical issues than the East Coast.

In a 2010 study, Jacobson and Dvorak found that 200 percent of California’s current electrical needs could be met with wind power. However, wind farms would yield the greatest payoff far from the population centers of Los Angeles and the Bay Area. To power the West Coast with these offshore wind farms, larger transmission lines would be required.


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