The overwhelming majority of offshore wind farms in our waters today are comprised of ‘fixed bottom’ turbines. As the name suggests, these sit on top of foundations that have been physically driven into the seabed, generating power that travels via a substation back to land.
Generally speaking, offshore wind farms benefit from stronger and more reliable winds than on land, because they lie in locations where that wind is not interrupted by the heat from cities, or physically stopped by large mountains. However, the yield of coastal wind pales in comparison to those you can find further out to sea.
Around 80% of the world’s offshore wind generation potential lies away from the shore, over waters deeper than 60m. But in such extreme depths it becomes more difficult or actually impossible to hammer turbine foundations into place.
So, over the last decade, floating wind technology has started to emerge. Rather than connecting directly to the ocean floor, this technology instead consists of a floating foundation with a turbine on top, tethered to an anchor in the depths.
Not only does floating wind allow greater flexibility to install wind parks where the flows are strongest and most reliable, it also removes many of the restrictions presented by fixed bottom turbines, such as the need for shallow water and a specific type of seabed – meaning more countries will be able to benefit from it.
However, the structure of floating wind assets is significantly different to fixed bottom designs: its foundations weigh thousands of tonnes – sometimes over ten thousand. To date, there have been multiple successful prototype projects using different foundation designs, but each of these have only installed a small handful of turbines.
To unlock the potential of floating wind, the most effective methods of constructing wind parks at scale must be established as soon as possible, and standardized. Given their high potential yield, floating wind farms provide a fast route to de-carbonize the world’s energy supply - and engineered heavy logistics will play a central role in achieving this.
Efficient Fabrication and Load-out
A complete floating wind farm turbine consists of a floating foundation, manufactured by specialist fabricators, and the turbine tower, nacelle and blades, manufactured by a wind industry OEM. While the manufacturing process remains similar for everything above water, the sheer size of each floating foundation will mean huge changes to its supply chain, logistics and launch.
Facilities that fabricate floating foundations will face demand to increase production rates as the sector grows. What’s more, given the broad similarity between floating foundations and petrochemical modules, competition for facilities will be high as they will require the same facilities, equipment and personnel to build.
Space needed for the storage of these giant foundations will challenge even the largest facilities, ultimately opening the market up to new entrants. Clearly, storing foundations that can measure 100m square on land will not be a viable long-term option, and will mean that manufacture and logistics must go hand-in-hand.
Then there is the task of managing the load-out of these huge structures, akin to the demands seen during modularized projects for the petrochemical sector. The industry will need to look beyond Europe to locations such as Southeast Asia, China and the Middle East to make best use of the facilities available.
Using multiple fabricators in several locations will allow more of each project to be undertaken in parallel, and by specialist facilities - shortening the schedule of projects and therefore increasing cost-effectiveness. This, in turn, will increase the viability of projects and allow more of them to move forward.
When fabrication of foundation is complete and it’s time to get them in the water, there are further challenges. For one, this must be achieved for the most part without the use of dry docks, as the majority of these will be unsuitable for objects of this size. Ports of a suitable draft are also needed, typically around 12m or more.
Choosing the right partner to handle lifting and load-out operations will be crucial if developers are to best manage risk and increase the cost-effectiveness of projects without being tied to one particular region.
Luckily, the expertise that has been used in the past to load-out modules of over 40,000t can be re-deployed to match the needs of floating wind, as foundations grow ever-larger.
Upgrading Ports to Accommodate Floating Wind Projects
Of course, once floating foundations have been fabricated, they must be transported to a port close to the wind farm location so that the turbine can be integrated on top of it. To achieve this, foundations may travel halfway around the world on top of transport vessels.
Here, projects will face similar challenges of size and scale. Establishing efficient port operations at scale will be critical for the industry to reach a mature model.
This will mean ensuring there are a sufficient number of ports worldwide that can offer the large areas of land, good maritime access and necessary ground capacity required to integrate and launch foundations. The sponsor country may also need to develop their facilities to meet the demands of the industry.
But many ports will face multiple issues when measured against these criteria; given the volume of expected floating wind work it is likely that the they will need to rely on facilities that have not been designed for offshore wind projects.
The space required to handle multiple floating foundations as large as 100m2 and 16,000t is not to be found at many ports - especially those designed for other, smaller scale projects. And of course, floating wind projects will still need significant real estate to handle tower sections, blades and nacelles.
Furthermore, even where ports have the space to accommodate these dimensions, they may not have the required ground strength to withstand the assembly and launch of components.
This means that many ports will need to upgrade in order to accommodate floating wind projects - but facilities will want to see a reliable pipeline of projects and the prospect of significant returns before they consider investing in the work required. So, project-based upgrades that can deliver the required capabilities on a temporary basis will be preferred.
Mammoet’s Enviro-Mat additive can be added to the native soil on site to produce a flat heavy lifting surface capable of withstanding 50t/m2 of pressure. Innovative marine engineering allows large components to be brought ashore in shallow water via an intermediate barge.
Other temporary upgrades can be used to facilitate floating wind. For example, docks can be strengthened using additional piles driven into the existing quay – without touching the water at all, where the permitting process is tougher. This can help to create the foundations necessary for heavy lift equipment to be used, turning any port into a floating wind terminal.
Many of the above measures can be achieved for a fraction of the cost necessary to permanently upgrade infrastructure, allowing ports to turn capital expenses into operational expenses and hence participate in more projects.
Launching 16,000t Components
With weights of anything between 3,000t and 16,000t, the launch of floating foundations is far from simple – the key challenge being to find a safe, cost-efficient and scalable method for placing large units in the water.
To date, a range of different solutions have been used to perform launching and one common approach has been the use of semi-submersible vessels. But there are questions over whether enough vessels will be available to meet demand, and whether they will be cost-effective when hired over a long period of time, during which they will be stood idle for long periods.
So, what are the solutions for projects where this is not a suitable - or available - option? Mammoet has found that moving foundations directly into the water is the most effective method of launching, as opposed to the use of transition equipment such as a floating platforms.
A promising methodology is to use a hybrid approach, whereby the floater is lifted from both land and sea and lowered onto the water directly at the quayside. Made possible by new technology such as Mammoet’s 6,000t SK6,000 crane, a hybrid approach offers a number of advantages.
As components are placed directly into the water right next to the quay, the process takes less time, is therefore less costly and requires less auxiliary equipment – generally needing only commonly available grades of barges.
Super Crane Capacity will be Key
With water depths at sea ruling out assembly solutions such as jack-up vessels, the most efficient way to integrate turbines onto floating foundations is to position the floater in the water directly alongside the quay, and piece it together using a large crane. But crane assembly presents its own challenges.
As I’ve mentioned, the largest floating foundations can be 100 meters square. If the turbine lies close to the center of the foundation, the lifting radius required could be as much as 55m – that is, half of the foundation’s width plus the space between quay edge and crane. At the same time, nacelle weights are expected to reach 1,000t in the near future, and hub heights a staggering 170m. This means that even the largest of crawler cranes are no longer sufficient, and that far fewer suitable cranes are suitable than the market may realize.
Given that a large capital expenditure investment to purchase a suitable crane is unlikely to be an appealing option for many, Mammoet recognized the market needed support to provide greater lifting capacity and address this bottleneck.
The SK6,000 crane has been designed with exactly this type of challenge in mind. Capable of lifting over 4,000t to a height of 175m and with a maximum reach of 144m, it can lift some floating foundation types directly into the water and also assemble wind turbines - all from a single position – turning the quayside into a highly efficient production line.
Mammoet is also exploring suitable alternatives to crane lifting. Project Elican, in partnership with our customers in the H2020 consortium, is looking at other ways to carry out turbine assembly. For example, the use of a telescopic crane mast that uses remotely operated strand jacks which are later raised at sea.
If this proves successful it would reduce the industry’s expected reliance on the small number of large cranes and help to alleviate potential supply issues. This idea was developed due to early engagement with Siemens Gamesa at the FEED stage of a project, highlighting the value possible when project phases are considered holistically.
Maintenance Needs Innovation and Experience
It is estimated that around 25% of floating wind turbines will have a maintenance incident during their lifetime, creating significant pressures on operational expenditure budgets. With thousands of turbines being installed in the coming years this is a key consideration for the industry.
Whilst in some cases turbines can be brought into port to conduct maintenance, the limited availability of suitable vessels and port facilities means that in most cases this work will need to be conducted in situ. This could also lead to large periods of downtime on a key asset.
To reduce this downtime and also risk, maintenance should be performed as much as possible at sea. This will mean meaning moorings do not need to be unlashed, and turbines do not need to be towed to their port of origin, which may no longer be available in any case.
Mammoet’s Conbit operation offers specialized expertise in performing repairs to offshore assets in situ and has developed a modular solution that offer important advantages for floating wind. This attaches directly to the turbine itself, making it possible to execute certain types of maintenance and modification operations at the wind farm itself.
This new 200t modular lifting system facilitates an even greater range of maintenance work without the use of a crane vessel. With only the facilities found at a fishing port required to launch the system, it offers a rapid response solution to lifting equipment such as motors, gearboxes, generators and shafts. It is of course also much more cost-effective compared to the typical costs for a crane vessel.
Developing Floating Wind at Scale
The huge potential of floating wind is beginning to be realized, but all elements of the industry’s supply chain must work together to establish the most effective and scalable way forward to fully deliver on this promise.
Mammoet’s expertise both in offshore renewables and other relevant heavy industry sectors can provide proven knowledge, methodologies and equipment – creating a drag-and-drop advantage for your floating wind project.