Floating Wind Farms on an Upward Wave

Floating Wind Farms on an Upward Wave

By Marla Keene, AX Control Inc
Now, however, many green energy companies are looking toward a new kind of offshore wind turbine that won’t need a concrete foundation. This new technology allows a turbine to float instead of sitting on the ocean floor.
Offshore wind farming has been part of renewable energy collection for almost three decades, long enough for the world’s first traditional offshore wind farm, Vindeby, located off Denmark’s coast,  to be recently decommissioned and dismantled after decades of use.  Orsted, who owned the site, stated the decommissioning went smoothly but took longer than expected because of foundation and concrete rubble removal.
Now, however, many green energy companies are looking toward a new kind of offshore wind turbine that won’t need a concrete foundation.  This new technology allows a turbine to float instead of sitting on the ocean floor. Not theoretical, this type of turbine is already a reality and has been hard at work off the coast of Portugal since late 2019 as part of the European Windfloat Atlantic project.

How Do Floating Wind Turbines Work?

Unlike traditional turbines that are built upon a concrete pier attached to the bottom of the ocean, floating wind turbines are built much in the same way as deep sea oil rigs.  The turbines are built upon a floating platform that is filled with ballast to offset the weight of the turbine above.  This platform is attached to the seabed using heavy mooring lines that give the massive turbines--often half the size of the Empire State Building--the security to withstand 60-knot winds and 55-foot waves.  The minimization of movement also factors into the efficiency of the turbine; too much movement of the base can negatively impact output.
Floating turbines typically use one of three kinds of bases: a single-legged, horizontal spar-buoy base, a semi-submersible base similar to those often used for offshore drilling rigs, or tension leg platforms that rely on the stiffness of tethers connected to each of its underwater corners.  94% of current offshore wind projects use semi-submersible platforms.

What are the Advantages of Floating Wind Turbines?

One of the primary advantages of this kind of wind turbine is the reduced cost of installation.  Since much of the turbine can be assembled on land and towed out to sea where it is then constructed at the anchor point, there are significant cost reductions in their construction as compared to traditional offshore wind turbines, where much of the construction has to be done on-site.  
Additionally, since floating turbines don’t need to be anchored directly to the ocean floor, they can be moved further out to sea, where winds are steadier and stronger.  Anchor chains allow attachment to the seabed at depths that were previously impossible, up to 300 feet.   A single deep sea floating turbine can produce up to 25MW of power per year, nearly seven times that of a traditional offshore turbine.
Traditional offshore turbines often raise environmental concerns related to the risk of collision with shore birds and the disruption to the marine environment at their base.   Additionally, those who live nearby on the shoreline may complain about noise created by the turning blades.  
By moving turbines further away from the coastline, delicate ecosystems close to shore can be better protected. Additionally, developers like Hywind Scotland work to identify sites that will not adversely affect birds, fish, or other marine life before moving turbines into place.  They also run studies on impacts to shipping and navigation and on the visual impact of their project to those onshore.  
There are still disadvantages to floating turbine systems.  Chain attachments still need to be tied to the seabed.  The attachments, chains, and the platform itself are outliers within the aquatic environment that may cause any number of disruptions--however small--to occur. Additionally,  present turbine technology is limited by top wind speeds, making them unsuitable for hurricane-prone areas.  

How Can Floating Wind Turbines Impact the World’s Energy Needs?

There are currently eight floating offshore wind farms in operation around the world and an additional fourteen projects in development.  Their combined output will come close to 250 MW annually.  More projects are sure to come as developers access parts of the ocean--including much of the US west coastline--where water depths are too great to support conventional fixed-bottom wind turbines.  West coast projects could help California reach their expressed 100% renewable energy goal by their goal date of 2045.  Forecasts estimate significant growth in the wind industry as commercial-scale floating projects off the west coast of California as well as another off Maine’s coastline continue to develop.
According to IRENA, the US Department of Energy has committed to $28 million in funding for offshore wind turbines through their ATLANTIS program (Aerodynaic Turbines, Lighter and Afloat, with Nautical Technologies and Integrated Servo-control.)  Such funding combined with improving technology and a change in energy policy will help transform the renewable market in the coming decades.  
Roughly half of the world’s population lives within 125 miles of a coastline, placing demand close to offshore wind production locations. Short transmission lines to on-shore power grids will prevent electricity from needing to be transmitted across long distances to reach local demand.  As the world looks to change over more of the energy market to renewables, floating offshore turbines will be well-placed to meet the growing demand.

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