Floating Offshore Wind Platforms - The Next Step for Offshore Wind

Floating wind has great potential. This technological advance will allow offshore turbines in deeper water (50-200m) than currently possible for fixed-bottom installations, allowing access to higher wind speeds. As much as 80% of the total potential for offshore wind power is believed to be in deep waters. The US, being bookmarked between two seas, has plenty of locations suitable for floating wind farms, particularly off the West Coast where the continental shelf falls steeply below the Pacific Ocean. It has been estimated that the floating wind resource of the US is 2,450 GW, which is a potentially massive opportunity.

How Can We Exploit the Resource?

“As installed capacity increases and the low-hanging fruit of shallow near-shore sites is exhausted, projects will need to be developed further from shore and in deeper water, which will pose greater technical challenges and constrain efforts to reduce costs. In response to this challenge, momentum is building around the potential for floating offshore wind foundation technology to unlock near-shore deepwater sites at a lower cost of energy than far-shore fixed-bottom locations."  Floating Offshore Wind: Market and Technology Review, Carbon Trust

Advantages of floating offshore wind:

  • Available deepwater sites close to shore
  • Support conventional HVDC transmission
  • Utilise nearby ports for support and O&M
  • Lower installation and major repair costs

Technological innovations, combined with various non-technology innovations, like different site choices, new market strategies and refined tools to reduce finance risks, should decrease the LCOE for offshore wind farms to USD 95/MWh by 2030 and USD 74/MWh by 2045. This excludes the potential impact of game-changing technologies. Such reductions should put offshore wind firmly in the portfolio of technologies needed to decarbonise the energy sector in a cost-effective manner.” IRENA Innovation Outlook Offshore Wind 2016

Technology Synergies – The Way Forward

The oil and gas industry has successfully operated floating platforms for years for producing oil & gas in deep water locations. Most of the components for the turbines and their transmission network are the same as for fixed-bottom installations.

As is often the case with emerging technologies, funding for the first experimental stages is difficult to obtain from private sources. Public funds are often needed to bring the projects from a developmental prototype to working models until the market is ready to back a commercial array. Scotland, Portugal, France and Japan and others have greenlighted small demonstration projects.

The Wind Resource off the US Shore

Hywind’s 2.3 MW demonstration in Norway has achieved average load factors of up to 50%, compared with 35-40% in conventional fixed-bottom offshore turbines and 25-30% in typical onshore turbines. The higher and more consistent wind speeds make this a valuable resource. Studies by EWEA (2013) and DNV-GL (legacy GL Garrad Hassan, 2012) using cost estimates from industry suggest that floating designs could be competitive in terms of the levelised cost of energy (LCOE) with fixed-bottom foundations in water depths greater than 50m.

It seems that there are many deep water locations appropriate for floating wind platforms off US shores, particularly around the West Coast, but the challenge is identifying sites near to good infrastructure such as grid connection or port facilities, and then obtaining consent for these sites.

Technologies

There are three dominant typologies (semi-submersible, spar-buoy, and tension-leg platform - designs adapted from the oil and gas industry), each with different strengths and weaknesses, influenced by site conditions.

Over 30 concepts are currently under development, with two-thirds emanating from Europe, though the emerging offshore wind markets in Japan and the USA are also very active.

While DNV-GL standards have been dominant in Europe, the American Bureau of Shipping (ABS) have developed similar sets of guidelines which have been adhered to by concept designers in the United States. The documents provide guidance on the design, construction, and installation of floating wind structures, addressing all aspects of the structure apart from the RNA (rotor nacelle assembly). These standards guides are available here.

Ecological concerns

As these are new technologies, we do not know how they will interact with marine creatures, seabirds and the flora of the sea bottom. It seems likely that the smaller footprint of floating structures will be less intrusive than fixed-bottom units. However, this needs research on actual installations and will take a significant amount of time before the full data on ecosystem impact is available.

Operational and Maintenance advantages

Because these structures float, taking them out to sea, bringing them back for repairs, and finally decommissioning them, appears to have very significant cost savings, because conventional vessels such as tugs can be used, obviating the need for specialised DP or jack-up vessels. This will mean that all shipping will be compliant with the US Jones Act (see previous blog here).

Testing

The Wind-Wave Basin at the University of Maine is a 1/50 scale tank which will enable designers to test their prototypes in a wide variety of wind and wave conditions, and variable depths. The basin is 30 meters long by 9 m wide (98 x 30 ft) and has a working depth of floor of 0 metres to 4.5 metres. The basin contains a 16-paddle wave generator, a beach, a moving wind wall, and an adjustable floor. The University claims it is capable of simulating in miniature, the worst possible storms at sea. Certainly, this facility and the FloWave simulator at the University of Edinburgh will be vital to prove designs before taking them out to brave the ocean environment.

Conclusion

Although the US Offshore Wind market is far less developed than other regions and will, therefore, offer a new horizon for existing companies at every level of the wind energy supply chain to sell their products, there are considerable possibilities for floating offshore wind in the near term – in the more distant future, it is likely that major commercial wind farms will be deployed as floating platforms in deeper waters with better power production than is possible close to shore.

Click here to read more about the Boston US Offshore Wind 2019 Conference and Exhibition. 

By Julian Jackson

 


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