Floating offshore wind energy

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Huge swathes of ocean used to be out of bounds for wind turbines, as their foundations could only be built in depths of up to 60 m. Not anymore.

How it works 

The technology that moors floating giants 


An offshore wind turbine weighs a thousand tonnes, is nearly as tall as the Eiffel Tower, and has blades as long as football pitches. How do we make these colossal structures float and stay stable amid high winds and strong swells?


The answer is huge, buoyant floating foundations and multiple solid anchor points on the ocean floor. There are currently a few different designs suited for different environments.


Floating designs and their advantages and disadvantages

Floating offshore wind foundation designs, their advantages and disadvantages

1. Tension-leg platform 
  

Pontoon based structure anchored with a tensioned mooring system that goes straight down to the seabed.

Advantages and disadvantages: 
The structure is lighter than other types, has a smaller mooring footprint and is the most stable once installed, but it can also be less stable to install and transport due to its lighter design.
 
2. Semi-submersible

Column and pontoon based structure anchored to the seabed with a spread mooring system.

Advantages and disadvantages:
Versatile design that fits many different conditions and is relatively simple to install, but the structure can be complex to build and is less stable than other designs.
 
3. Barge
  

A hull structure with a large surface area in contact with the water – the principle is like that of ship design. Anchored to the seabed with a spread mooring system.

Advantages and disadvantages:
Like the semi-submersible, the barge is versatile and relatively simple to install, but less stable than other designs. The barge has the potential to use traditional shipyard building techniques.
 
4. Spar buoy
  

A vertical cylindrical structure with ballast at the bottom for stability. Anchored to the seabed with a spread mooring system.

Advantages and disadvantages:
Can be simple to build and has good stability. However, owing to its depth it requires a very deep harbour to install the turbine or, for offshore installation, a deep-water installation vessel.  

Find out more about the technology of floating offshore wind  

Growth 

A new leap forward for renewable energy 


As much as 80% of the global offshore wind resource potential is in waters with depths exceeding 60 metres, according to the International Energy Agency. That’s why at Ørsted we’re expanding into floating wind, as a complement to our seabed-fixed business. It’s another step towards our vision of creating a world run entirely on green energy.  

We believe in trying new things. When we built the world’s first offshore wind farm in 1991, people thought it wouldn’t work. Offshore wind now brings renewable power to millions, and we’re proud to have the largest installed capacity in the world.   

We will bring this experience to floating wind – and help to make it cost-competitive and sustainable. We’re looking forward to working with others to make this happen.  

The challenge of floating wind 

Floating technology is still relatively expensive because it’s new. It’s in its early stages and has not been deployed at a commercial scale – yet. But with our experience, we can help make floating wind commercially viable.  

We must work together across the industry, partnering up with supply chain companies and combining our expertise to scale construction. We will need policy support and major government investment in areas such as new deep-water port infrastructure to spur the private investment needed.

Benefits 

Key benefits of floating offshore wind power

Climate targets 

Floating wind brings offshore power generation to deeper waters, which are abundant. Regions where seabed-fixed turbine foundations are impractical can now look into floating foundations – from the Pacific Ocean off the coast of California to Japan. And in deeper waters, wind speeds are often greater, meaning more power. 


Jobs 

A modern 1 GW seabed-fixed wind farm creates more than 18,400 direct and indirect jobs in development, construction, operation, and decommissioning. We expect floating wind to be similar. 


Biodiversity 

Each wind power solution has its benefits. Floating turbines can be installed less noisily, with smaller vessels, and further from bird migration routes. Seabed-fixed turbines can host biodiversity projects such as ReCoral. 

Our projects 

Ørsted’s floating offshore wind projects   


See the list of our floating offshore wind projects   

FAQs 

Frequently asked questions about floating offshore wind energy 

  • How big are floating wind turbines?  
    Floaters are massive structures. Steel floaters for a 15 MW turbine could typically weigh 3500 to 4500 tonnes while concrete floaters would be in the range of 17,000 to 22,000 tonnes. The width of some floaters can easily be more than 100 metres! 
  • Do floating wind turbines move?  
    Yes, and movements can be significant (except for with tension-leg platforms). A rule of thumb is that floater design should limit sideways movement to around 30% of the water depth, to protect the dynamic cables.
  • How are floating wind turbines anchored to the seabed?  
    The floaters are anchored to the seabed through mooring lines, which are often made of chains, but can also be made from polyester or nylon ropes.
  • What happens if a mooring line breaks?
    Mooring lines can break or get too fatigued to function properly. This is well known already from the oil and gas sector. To address this risk, systems are designed to have redundancy – in other words, extra mooring lines – so the whole system can handle failure of a mooring line. With floating wind foundations, due to the large amount of positions needed and the need to achieve low cost of electricity, the designed redundancy will likely be less. Modern monitoring systems of mooring line fatigue and technologies such as digital twins can also be used to decrease the risk that a mooring line breaks instead of being replaced as part of planned maintenance. 
  • Can a floating wind turbine tip over and fall?
    In principle, floaters are designed to be self-stable and are designed for extreme weather and sea conditions. Ørsted also requires that floaters are designed to withstand a ship impact.
  • How are the floating wind turbines connected to the electrical grid?
    They are connected via electrical cables similar to those for seabed-fixed offshore wind. However, the cables for floating wind are not buried as is the case for seabed-fixed. Instead, the cables float, which enables them to handle the movements of the floating foundation. 

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