Innovative technology for the world’s largest wind yield Floating offshore projects: the long road from the idea to the successful model

13.04.2023 7 Reading Time

The fate of many thought leaders is that hardly anyone believes them or almost nobody wants to hear what they are saying. This is what happened to William Heronemus, Professor of Civil Engineering at the University of Massachusetts, who wrote the following in 1968: "In the immediate future, we can expect the ‘energy gap’ to result in a series of crises as peak loads are not met. 

The East Coast will be dependent on foreign sources for most of its oil and gas. The environment will continue to deteriorate in spite of ever-increasing severity of controls. […] In the face of the continuing dilemma: ‘power vs. pollution,’ a third alternative to nuclear and fossil energy must be sought. It may be found in the many and varied nonpolluting energy sources known to exist in the US or its offshore aggregate. These energy sources [...] could satisfy a significant fraction of our total power needs in the year 2000."1

William Heronemus first came up with the idea of a floating wind power plant in 1973 and two years later followed it up with detailed designs of offshore wind farms consisting of floating turbines.2

Pioneering technology for the world’s largest wind yield

Floating wind farms, also known as “Floating Offshore Wind Energy”, are wind turbines installed on air-filled hollow foundations that are anchored to the seabed with chains or lines. They are becoming increasingly interesting as an alternative to traditional offshore wind farms, whose foundations are driven into the seabed. 

On the one hand, they are more environmentally friendly, as lashing the floating foundations to the seabed causes less noise and dismantling does not require much effort. On the other hand, they offer the possibility of tapping into the 80 per cent of the world's wind resources that are located above waters more than 60 metres deep.

The following is so far undecided: competition of the systems

As the distance to the coast increases, so do the technical challenges. Although the development of floating foundations and their anchors is already well advanced, the perfect system has not yet been identified. The following three are considered to be favourites:

  • The spar buoy platform is based on a hollow body made of steel or concrete, under which there is a mass component up to 100 metres long, which gives the structure a low centre of gravity. At the same time, the floating units ensure that the wind turbine always erects itself again. If the wind blows particularly strongly, the wind turbine changes the angle of its rotor blades. The object is fixed to the seabed by three ropes. The disadvantage is that, as it requires around 200 metres of water, the installation is complex.
  • The barge solution consists of three drive units that lie so deep in the water that they have a stabilising effect even in strong winds. This construction prevents the wind pressure from tilting the tower too much. In order to further stabilise the wind turbine and its substructure, pumps automatically press water into the floating units facing the wind within seconds.
  • The tension leg platform has enormous excess buoyancy due to its large floats, which gives the wind turbine a force that is directed upwards. The steel cables that anchor the floating platform to the seabed with a 2500-tonne concrete block pull the entire structure down. Both forces, lift force and tractive force, act against each other and ultimately hold the platform in place.

It is not yet possible to say whether any of the three systems will prevail or whether several will continue to exist in parallel. The combination of various benefits is also currently being tested. The outcome remains to be seen.

Europe: more potential than the US and Japan put together

But no matter the outcome of the battle about the type of foundation, Europe has already positioned itself as a technology leader. This is not least due to the ideal conditions. The deep, windy waters on Europe's western coasts and in the Mediterranean guarantee large energy yields and at the same time short transmission distances thanks to their proximity to consumers. 

There is enormous potential, especially off the coasts of the United Kingdom, Ireland, France, Spain and Portugal with their steeply descending seabeds, deep waters and densely populated coasts. If the 2017 report by the European industry association WindEurope proves to be right, European waters have significantly more potential than the USA and Japan combined, with potentially 4,000 gigawatts of capacity.3

Norway is making a start, Portugal needs to do more

34 years were to pass after William Heronemus' memorable remarks before, in 2009, the first prototype of a floating wind turbine, "Hywind Demo", was installed in Norway's Åmøy Fjord. At wind speeds of up to 44 metres per second and wave heights of up to 19 metres, the plant ran without any significant incidents in the years that followed.4

Despite the leading edge gained from this experience, the Portuguese were ahead of the Norwegians with their floating offshore wind farm “Windfloat Atlantic”, which was commissioned in 2020. It marks the successful end of a decades-long project of the WindPlus joint venture and at the same time the beginning of a new Portuguese floating offshore era. Commissioned in October 2022, the 25-megawatt floating offshore wind farm, the Viana do Castelo, is just the forerunner of a test site that will unleash 500 megawatts of floating offshore power.5

The ultimate competition has begun

In 2021, Scotland was the first to be ahead of the curve with the 50-megawatt Kincardine offshore wind farm located 15 kilometres off the coast of Aberdeenshire. However, it was only able to hold the record as the largest floating offshore wind farm in the world for one year.6

It was then beaten by Norway’s Hywind Tampen with an output of 88 megawatts.7
Known for having nostalgia for nuclear, France has also discovered offshore wind power for itself and is currently building three floating wind farms in parallel – “Provence Grand Large”, “Eolmed” and “Les Éoliennes Flottantes du Golfe du Lion”.8

Sweden, an avowed enthusiast of renewable energy, has started the catch-up race. The Freja Offshore joint venture has four floating wind projects with a total capacity of eight gigawatts in the pipeline. At the same time, Simply Blue, Deep Wind Offshore, Njordr Offshore Wind and RWE have positioned themselves as ambitious offshore wind catchers.9

There are very pragmatic reasons why Germany has not yet played a role in this competition. In view of the rather shallow water depths in a radius of up to 120 kilometres, wind turbines installed on the seabed in Germany are much more cost-effective.