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Driving decarbonization with renewable floating offshore wind energy

March 14, 2024

By Ralph Kurth, John Crowther and Ken Fitzgerald

Floating offshore wind power can provide us with bountiful renewable energy in waters too deep for traditional fixed-bottom turbines. Here’s how.

The energy transition is driving the development of renewable energy sources around the world. And one of the biggest trends is the growth of the offshore wind industry. Offshore wind power has been a focus on the Eastern Seaboard of the United States (US) for years. There are several projects currently in development and a few that are already generating power.

In fact, the 800-megawatt (MW) Vineyard Offshore Wind Farm first started sending energy to the grid in early 2024. We’re especially excited for that project, as our team has worked as owner’s engineer since 2017. Additionally, the 130-MW South Fork Wind Farm began generating power at the end of 2023. It’s a project where our teams performed permitting services. After so much rigorous work, it’s exciting to see the progress we are making with this renewable energy resource.

However, there is only so much real estate possible for fixed-bottom offshore wind farms off the US East Coast. The region has other needs too. These include shipping lanes, fishery zones, protected areas, and more. So, what do we do?

We know we’ll need more offshore wind energy to reach our ambitious decarbonization targets. And the International Energy Agency believes that the offshore wind industry “will attract around $1 trillion of cumulative investment by 2040.” According to the National Renewable Energy Laboratory (NREL), more than 65 percent of total offshore wind resources lie in waters more than 60 meters deep. This means we need to focus on floating wind farms.

Floating offshore wind is an exciting and fast-growing renewable energy technology.

Floating offshore wind farms are proposed in the US on both the East and West Coasts, as well as in Canada. The Bureau of Ocean Energy Management (BOEM) conducted an offshore lease sale in California in December of 2022. Five lease blocks are currently in the planning stage off the coast of California in water depths averaging from 750 to 1,000 meters deep. BOEM is evaluating additional floating offshore wind lease sales for the Gulf of Maine and the Central Atlantic regions.

So, let’s dive deeper into floating offshore wind farms and how we can deliver these projects to drive the energy transition forward.

Traditional fixed-point turbines vs. floating technology

The continental shelf off the East Coast of the US has ideal site characteristics for traditional fixed-bottom offshore wind farms. Why? Because the shelf is gradually sloping and most areas of the shelf are less than 60 meters below the surface. Fixed-bottom turbines are driven directly into the seabed. With current technology, it is only possible—and cost effective—to install fixed-bottom foundations at water depths up to 60 meters deep. Essentially, floating windfarms would only be constructed farther off the coast in deeper waters and in areas that don’t impact the coastline or the activities taking place there. That works well for the East Coast. But fixed-bottom foundations are not feasible in the deeper water on the West Coast.

On the US West Coast, the water depth drops off much more quickly. This is because the continental shelf is much narrower. The proposed wind farms in the region are approximately 15-30 miles away from shore, where the water depths can exceed 1,000 meters in some places. So, traditional fixed-bottom turbines aren’t possible there yet. But floating turbines are.

Floating offshore wind turbines are a fairly new concept. In fact, there are only a handful of floating offshore wind farms in the world. But that number is set to rise as offshore wind becomes a bigger piece of the renewable energy puzzle. Unlike fixed-bottom turbines, floating turbines sit atop buoyant platforms. The platforms are anchored to the seafloor using a variety of technologies. This allows for deeper-water installation.

Let’s explore the main floating offshore wind technologies below.

An illustration of offshore wind technologies.

Types of floating offshore wind technologies

As we said earlier, floating offshore wind is a relatively new trend. They still generate renewable wind power just like traditional fixed-bottom turbines, just in different geographic regions. Right now, three primary technologies are used for floating offshore wind farms. These include semi-submersibles, spar buoys, and tension leg platforms.

  • Semi-submersibles are currently the most prominent technology used for floating offshore wind turbines. They have a large floating base that is complimented by stabilizing columns. It essentially functions as a large floating platform. This was among the first technologies used for floating turbines.
  • Spar buoys are floating cylinders that extend deep under the water's surface. Also known as a ballast-stabilized system, spar buoys provide the ability to remain stable during weather events or rough waves. Cables anchor the spar buoys to the seafloor so that the turbine platform stays in relatively the same spot amidst waves.
  • Tension leg platforms have a floating base that is tethered to the seafloor with tensioned mooring lines. The offshore oil and gas industry has used the technology for anchoring drilling facilities in place.

Again, different site characteristics will call for different floating offshore wind schemes. And while these are the three most common kinds of technology right now, evaluations continue on other configurations and technologies. And we expect to see new and evolving innovations as the industry grows. So, when and how can we expect the floating offshore wind industry to boom? Is there anything holding it back?

By developing floating offshore wind projects, we can give the industry the ability to move these wind farms farther from the shore.

Challenges to overcome for floating offshore wind

It’s clear that there is an optimistic future ahead for floating offshore wind. However, there are several challenges to widespread adoption, as well as some questions that need answering. And we will need to address these issues if we hope to expand the industry. Let’s review a few of them below.

The first challenge to widespread adoption is technology. Although there are pilot projects around the world, development continues for a lot of the technology for floating offshore wind. The current projects constructed are in water depths ranging from 60 to 300 meters deep—and future projects will be in even deeper water. There are more than 40 iterations of the technology for floating offshore wind turbines and platforms. There also is no real supply chain to support widespread adoption just yet. We will likely leverage a lot of this technology from the oil and gas industry, borrowing from existing floating platforms utilized in offshore drilling.

The second challenge is cost. Right now, the cost of materials for floating offshore wind is higher than fixed-bottom technology. This is also in part due to supply chain constraints. It is expected these will come down over time. The technology for fixed-bottom turbines has been developed for more than 20 years and the supply chain has been developed to support it. That will change as we move these wind farms farther out into the ocean.

Next up is transmission. When dealing with a structure that is floating, there will be motion and movement of the turbine. This is especially true under severe weather. These conditions will impact the type of equipment needed to withstand the elements and will be factored into design. For instance, the cables needed to transmit the energy back to the shore to connect to the grid need to be designed to handle the movement from the inherent nature of the ocean. Lower power dynamic cables have been used for floating offshore oil platforms for many years. But these projects will require developing dynamic export cables capable of transmitting higher power levels to get the power from the floating wind farms back to shore. For longer distances, it may be advantageous to use high voltage direct current (HVDC) transmission. Using HVDC transmission will require floating HVDC converter stations to convert the alternating current power generated by the wind turbines to DC for efficient transmission to shore.

The onshore grid design is also a factor. For example, in California, the electrical grid is mostly located centrally within the state and in the major load centers. That means there are few points close to the shore for an offshore wind connection. Considering California’s ambitious energy goals, they will require significant onshore grid modernization and transmission development to effectively integrate the floating offshore wind resources into their network.

Another key factor is the environment where the floating wind farms are located. Several factors go into these projects to promote strong environmental stewardship. These can include limiting disruption to the seafloor, maintaining the shoreline, and protecting ecosystems and marine life. We must address all of these issues for the floating offshore wind industry to flourish. 

Protecting marine life is essential to the development of floating offshore wind farms. 

Floating offshore wind and the energy transition

We have set some bold and ambitious decarbonization targets that we will strive to reach over the coming years. And it will require an all-hands-on-deck approach to renewable forms of energy. Offshore wind power has a big role to play in the energy transition. And while there is limited space for traditional fixed-bottom turbines, floating offshore wind farms can really step in to make a difference.

According to NREL, the global pipeline for floating offshore wind energy increased by nearly 42 gigawatts in 2022. And while the growth is mostly attributed to new commercial projects in the United Kingdom, there are encouraging signs within the US too. NREL believes the US floating offshore wind energy market reached a turning point in 2022. This was due to recent climate legislation like the Inflation Reduction Act, as well as the US Department of Energy Wind Energy Technologies Office announcement of the Floating Offshore Wind Shot. That is an effort to lower costs of floating offshore wind by 70 percent.

Floating offshore wind is an exciting and fast-growing renewable energy technology. By developing floating offshore wind projects, we can give the industry the ability to move these wind farms farther from the shore. And as we unlock more areas for development, countries around the world can increase their capability to achieve their renewable-energy and emissions-reduction goals. This will make a meaningful impact on the energy transition, and the planet will be all the better off for it. 

  • Ralph Kurth

    Ralph is currently focused on HVDC transmission systems, ac substations, and their automation systems. He has served as technical advisor, project manager, and commissioning manager on several technically advanced projects around the world.

    Contact Ralph
  • John Crowther

    With over 30 years of experience in environmental engineering and consulting, John now leads our offshore wind business in the renewable energy sector.

    Contact John
  • Ken Fitzgerald

    Ken has over 30 years of experience in the power industry. He has executed and managed multiple projects as owner’s engineer, as well as many projects as an EPC contractor.

    Contact Ken
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