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| The Nystead wind farm off the coast of Denmark consists of 72 wind turbines built on monopiles. (Cape Wind) |
With increased demand for sustainable energy sources, wind power is beginning to establish itself as a viable alternative in the United States.
According to the American Wind Energy Association (AWEA) in Washington, D.C., total U.S. wind power capacity as of March 31 was 11,699 megawatts, or about 0.7 percent of the U.S. electricity supply. Small as that might be, this total reflects yearly increases in output of about 2,400 megawatts in 2005 and 2006. For all of 2007, the association projects an increase of about 3,000 megawatts, all of it from land-based wind farms. At present there are no offshore wind farms operating in the United States, but that may be about to change.
Several offshore wind farm projects are under review and awaiting approval. Of these, a proposal by Wind Energy Systems Technologies LLC (WEST) appears the most likely to move forward quickly. The company, which is based in New Iberia, La., has many of the necessary state and federal permits in place and has already signed a lease with the Texas General Land Office for a site in the Gulf of Mexico seven miles from Galveston.
The $300-million project will be located on an 11,355-acre block. Called Galveston-Offshore Wind LLC, the project would be able to generate 150 megawatts with 50 to 60 turbines, or enough to power over 40,000 homes. Plans call for the capacity to eventually be doubled to 300 megawatts.
Unlike other proposals for offshore wind farms that have met opposition from politicians, shorefront property owners, environmental groups and recreational boaters, Galveston-Offshore Wind has been able to overcome many of the obstacles that have stalled other projects, such as those proposed for Nantucket Sound in Massachusetts and the Delaware Bay.
Herman Schellstede, WEST’s president and chief executive, and his firm, Herman J. Schellstede & Associates, have been in the offshore oil and gas industry for almost 40 years. Drawing on their experience building platforms in the Gulf they have assisted WEST in the design of the towers, platforms and cabling.
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| Wind Energy Systems Technologies has installed a tripod tower in the Gulf of Mexico of the type it expects to use for its 150-megawatt project.(Wind Energy Systems Technologies) |
The towers would be between 262 and 328 feet high at the hub of the rotor. Schellstede said that monopile towers (those built on a single tube driven deep into the seabed) are not a good choice for the Gulf, given the frequency of hurricanes.
“Monopiles tend to move and fail due to hurricane conditions,” he said. “There are currently about 6,000 platforms off the coasts of Louisiana and Texas. Most of them are either tripod, four-legged or eight-legged. These frame designs have been an excellent solution to the survivability of the offshore platforms in the Gulf of Mexico.”
WEST has already installed one tripod tower off the Texas coast to gather meteorological data to determine the feasibility of the site.
Given the costs, complexities of offshore construction and public opposition, it is no surprise that offshore wind farms have been slow to come on line in the United States. Some opponents have deemed wind farms eyesores when viewed from valuable coastal properties, whereas land-based farms are typically located in very rural areas. They have also been called a risk to migratory bird populations. Critics have also described them as hazards to marine and air navigation because they may block out line-of-sight radar signals in the immediate area. However, most wind farms are located in fairly shallow water and away from shipping lanes or below the altitude at which most planes fly.
Another serious obstacle to development is the overall cost of construction, since the cost of building in a marine environment is roughly 50 percent higher than building on land, according to Stan Calvert, chief engineer with the U.S. Department of Energy’s Office of Wind and Hydropower Technology.
In the United States offshore wind farm development will rely heavily on marine construction technologies already pioneered in the Gulf of Mexico by the oil and gas industry. Companies like Shell Wind Energy are building on their oil and gas expertise. According to AWEA, Shell Wind Energy has participated in the development of an offshore wind farm in the North Sea.
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| This image shows how the Cape Wind project, which would be built on monopiles, would appear from the shore of Cape Cod at a distance of 5.6 miles.
(Cape Wind)
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There are companies, like the Danish marine construction firm A2SEA, that specialize in wind farm construction with specialized heavy-lift vessels and deck cranes to handle blades and turbines the size of two city buses. Specialized cable-digging devices called jet plows bury the electrical cables between the towers and the shore-based substation. These devices dig trenches utilizing high-pressure water to fluidize the sediment. A small amount of sediment is introduced into the water column during the process and subsequently settles back to the sea floor, burying the cable with minimal impact on the marine environment.
There is also the issue of maintenance. Even though the towers are operated and monitored remotely, vessels would be required to transport maintenance crews. Weather is also a factor, since work would be dependant on wind and sea conditions.
Despite the opposition and the complexities, wind power projects are being proposed in the United States. In the Northeast, Cape Wind, an offshore wind farm proposed by Boston-based Energy Management Inc., is planning a 468-megawatt wind farm on Horseshoe Shoal in Nantucket Sound.
According to Cape Wind spokesman Mark Rodgers, Cape Wind proposes to install 130 monopile towers that would be 250 feet high and 10 feet in diameter. Each tower would be equipped with a General Electric turbine turned by 180-foot-long blades. Each would be capable of generating 3.6 megawatts.
The Long Island Power Authority has proposed building a wind farm a few miles off Jones Beach State Park. This proposal consists of 40 3.6-megawatt turbines with an estimated generating capacity of 140 megawatts, or enough to power approximately 44,000 homes.
In Delaware, Bluewater Wind LLC wants to build a wind farm six miles off the Delmarva Peninsula. Bluewater plans to install Danish-built Vestas turbines on the towers and has chosen the construction and engineering firm Ballast Nedam of the Netherlands to build the project.
Bluewater Wind also has proposed wind farms in Rhode Island and New York waters.
