New material to keep wind turbines afloat

Nicola Brittain

Floating wind turbines are a viable alternative to those with fixed anchors, here we explore how they work.

Offshore wind turbines play a pivotal role in the advancement of renewable energy sources. However, about 80 percent of global wind resources are situated in waters with a depth of more than 60 meters. These are areas where wind turbines with fixed anchors in the ground face their limits. To harness this vast potential nonetheless, operators are increasingly embracing floating wind turbines. This trend also impacts material development. In regions with significant water depth, floating wind turbines require buoyancy modules to alleviate stress on high-voltage cables essential for transporting electrical energy. When the water is particularly deep, additional protection against cable damage is provided by rubber blocks inside the buoyancy modules. To ensure that these function reliably over a long service life, Freudenberg Sealing Technologies (FST) has developed a new ethylene-propylene diene monomer (EPDM) material that reliably withstands the high stress.

The Weinham based company has distinguished itself as a long-standing development partner to the oil and gas industry by developing and producing materials that reliably meet the challenges posed by seawater and high pressures, more recently it has begun developing solutions for the offshore wind industry.

New EPDM material

The polyurethane buoyancy modules keep the high-voltage cables in a so-called “lazy wave”, reducing not only the tension but also stress on the cables to mitigate the risk of damage. Starting at medium water depths (between 20 and 200 meters), the pressure can become so intense that rubber blocks inside the modules are needed to protect the cables from damage. This is always the case in so-called deep water (300 meters or deeper). These rubber blocks also secure the buoyancy module to the cable.

It may sound relatively simple at first, yet it’s anything but trivial. Experience gained in the oil and gas industry shows that the great temperature variations cause pipelines to undergo compression by up to 55 percent of their diameter, followed by expansion. Even if lower compression values can be expected for the differently designed wind turbine cables, the internal rubber blocks must act as springs to compensate for these movements. The buoyancy of each module, with a diameter of two to three meters, requires individual calculations. Scaling or transferring specifications to other system projects is difficult, as they must account for each of the prevailing underwater conditions and the various technical requirements. Consequently, system-engineering companies design and produce their own modules for each project. This requires great effort in terms of development, production and underwater installation, which is why the components are required to have a long service life.

Life span of wind turbines

While lifespans of up to 25 years are expected in the oil and gas industry, up to 37 years of reliable buoyancy without failures in the field are called for in the floating offshore wind sector. And this is where the materials experts at Freudenberg Sealing Technologies come into play.