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Offshore wind farming has picked up steam during the last decade, with more & more countries installing these gigantic turbines in their coastal waters. The largest wind farm in the world recently opened off the UK coast and the developement company, Ventall Group, plans nine wind farms in six countries between 2009 and 2011.
One of the largest offshore areas in the U.S. with shallow water is off Cape Cod, where a major wind farm has been approved.
The construction of these farms have given rise to a new class of ship: the Turbine Installation Vessel.
Turbine Installation Vessels (TIV)
The first purpose built TIV was the TIV Mayflower Resolution, currently known as the TIV Resolution & owned by MPI Offshore. This vessel utilizes both dynamic positioning & jack-up technology.
Equipped with 6 retractable legs, the Resolution will set up on location using DP, then elevated out of the water using the jack-up legs. This provides a stable platform to install the turbine on top of a previously prepared foundation. Once installed, the Resolution lowers back down to the water & moves to the next location, where the process is repeated. She has the capacity to carry 10 wind turbines.
What are the benefits to building offshore?
Offshore wind turbines are less obtrusive than turbines on land, as their apparent size and noise is mitigated by distance. Because water has less surface roughness than land (especially deeper water), the average wind speed is usually considerably higher over open water.
What about the cost?
Offshore installation is generally more expensive than onshore, depending on the location. Offshore towers are a fair bit taller than onshore towers once the submerged height is included, making the foundation more expensive to build.
Offshore saltwater environments also raise maintenance costs by corroding the towers, but fresh-water locations such as the Great Lakes do not. Repairs and maintenance are usually more costly than on onshore turbines, motivating operators to reduce the number of wind turbines for a given total power by installing the largest available units.
Offshore saltwater wind turbines are outfitted with extensive corrosion protection measures like coatings and cathodic protection, which may not be required in fresh water locations.
Transporting the components
Transporting large wind turbine components (tower sections, nacelles, and blades) is much easier over water than on land, because ships and barges can handle large loads more easily than trucks or trains. On land, large goods vehicles must negotiate bends on roadways, which fixes the maximum length of a wind turbine blade that can move from point to point on the road network; no such limitation exists for transport on open water.
Offshore wind turbines will probably continue to be the largest turbines in operation, since the high fixed costs of the installation are spread over more energy production, reducing the average cost. Turbine components (rotor blades, tower sections) can be transported by barge, making large parts easier to transport offshore than on land, where turn clearances and underpass clearances of available roads limit the size of turbine components that can be moved by truck.
Similarly, large construction cranes are difficult to move to remote wind farms on land, but crane vessels easily move over water.
What challenges must be overcome?
Offshore wind projects must strike a viable balance between technological and economic challenges.
Offshore technology has had to adapt to operate successfully in a more challenging environment. Tough weather conditions, which can limit access for routine maintenance, and the saline environment create the need for more robust turbine parts. This in turn means higher costs, which are not always offset by the higher productivity due to the higher offshore winds.
Continued operational R&D, and policy support that recognizes the value added from renewable energy projects like offshore and onshore wind, will go a long way toward resolving these challenges.
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