Kilometers off the coast of Basque Country in northern Spain, a new twist on offshore wind energy will soon face its final test. The Spanish firm Saitec Engineering made headlines late last year with its distinctive floating turbine concept, and promised to deploy a prototype in April. Last week, that launch took on new significance when Saitec announced a partnership with the renewables division of the German energy titan RWE.
The potential to harvest wind from beyond the shoreline is substantial. “The farther from shore [the wind farm is located], the bigger the wind resource is,” said Luis González-Pinto, chief operating officer of Saitec Offshore Technologies.
The deal is a mark of confidence in the ability of the new concept to bring Spain to the forefront of the growing offshore energy market. The BlueSATH project, a 1:6-scale model of a 2-MW floating turbine, is named for the most innovative feature of its design, the Swing-Around Twin Hull. Two hulls made of prestressed concrete join to form a structure that, from above water, looks roughly like a catamaran, with a steel “heave plate” suspended beneath for stability. A single-point mooring system with three cables anchors the structure to the seabed, allowing the floating section to swing, or “weathervane,” around the mooring in response to the flow of the water.
Like offshore oil drilling, offshore wind energy grew in part from the push to minimize the noise and disturbance to humans that turbines generate. But offshore wind trades social problems for technical ones. Anchoring something as heavy as an industrial-scale wind turbine to the seabed requires moving large amounts of expensive materials out to sea. And once a turbine is built, it’s difficult to repair.
Even in shallow waters, offshore wind poses a daunting engineering challenge. In recent decades, turbines have grown to staggering heights, seeking ever faster and more consistent winds. Offshore wind farms face high installation costs, which compel startups to partner with large energy providers to share the risk of developing new designs.
Offshore turbines have traditionally been supported by monopiles—huge tubes of steel, driven into the sea floor by hydraulic hammers and often weighted with ballasts of rock. The larger the monopile, the higher the cost. Switching to cheaper, lighter materials, like concrete, can improve the feasibility of an offshore project only up to a point. A guide on offshore wind power [PDF] sponsored by the British Crown suggests that keeping the monopile erect in waters deeper than 35 meters is technically and financially inadvisable.
“Bottom-fixed foundations are only feasible in zones with shallow waters, but most of the coastal areas in the world are located in waters deeper than 60 meters,” said González-Pinto.
Once the prototype BlueSATH turbine is deployed in April, the plan is to monitor it for 12 months as a final validation of the design. After the BlueSATH test is complete, a full-scale floating turbine (called DemoSATH) will be moored at the Biscay Marine Energy Platform (BiMEP), a test site for ocean energy collection technology, where waters rise up to 90 meters above the seafloor. The site feeds into the electrical grid at nearby Armintza and features an extensive ocean monitoring system, where Saitec engineers can track the prototype’s response to changing wave activity and various types of weather. The DemoSATH test will last 3.5 years.
It has taken four years of R&D and wave basin tests to reach this point. The new project began in the R&D arm of Saitec Engineering before it spun off into Saitec Offshore Technologies in mid-2016, a few months before the world’s first large-scale floating wind turbine farm (not affiliated with Saitec) was operational in Europe. The Hywind Scotland project, which consists of five 30-megawatt turbines off the coast of Aberdeenshire, Scotland, is still one of only two operational floating wind farms in the world.
Like Saitec, the Hywind design is inspired by the floating structures of offshore oil drilling equipment. It’s also based on an earlier turbine design sponsored by Equinor (then Statoil), the Norwegian state-owned oil corporation. Hywind became profitable last June thanks to a deal with its own European energy giant, Danske Commodities, which will buy the farm’s entire energy output for the next two decades. Other projects, including the first U.S. floating wind farm, are still in early stages.
According to González-Pinto, it’s only a matter of time before floating wind earns its place in the global energy market. “For the moment, there are only two floating wind farms with multiple floaters,” he said. “Nevertheless, projects are ongoing and the perspectives are gorgeous.”
This post was updated on 16 March 2020.