Saipem, the Italian oil and gas contractor, has unveiled a novel floating offshore wind substructure that will go into the water for testing off Ireland's west coast from 2022.

The "Hexafloat" substructure aims to be a one-size-fits-all foundation for a range of turbine sizes thanks to a hanging counterweight that can be lowered to stabilize heavier loads.

The counterweight, essentially a steel basket filled with several thousand tons of magnetite, will be suspended by synthetic fiber tendons from a 180-foot-wide, 1,300-ton hexagonal submersible floater made of welded steel tubes containing water ballast tanks.

The structure will be attached to the seabed via three or six simple mooring lines with drag anchors, and export cables will be attached in a lazy wave configuration, minimizing the need for seabed preparation.

To suit different turbine sizes, the diameter of the tubular structure will be “slightly adapted” and the ballast depth will be adjusted, said Lisa MacKenzie, marketing and communications manager at the European Marine Energy Centre (EMEC), which will lead the test program for the technology in the early 2020s.

Otherwise, the overall dimensions of the structure will remain similar regardless of turbine size. That will make it easier to move toward serial manufacturing of the substructure, helping to reduce the levelized cost of energy.

Trial set for harsh conditions

The concept has already been tried out in a test basin in 2018 and will next be put through its paces at full scale off the coast of Ireland in a 31-million-euro ($35 million) project called AFLOWT (for accelerating market uptake of floating offshore wind technology).

EMEC, which runs a marine energy technology testing center in Orkney, Scotland, will oversee the one-year testing program at a Sustainable Energy Authority of Ireland test site near Belmullet, County Mayo.

EMEC Commercial Director Oliver Wragg said the test site, which has significant wave heights of up to 17 meters (55 feet), is one of the harshest in the world.

“If we can prove one floating wind technology works off the west coast of Ireland, you’ve just opened up the market massively,” he said.

Designed for turbines up to 15 megawatts

According to a Saipem paper presented at a conference in Italy last month, the Hexafloat is based on a product specification that includes being compatible with turbines of up to 15 megawatts and the ability to be built at a rate of one a week.  

The product specification also stated the platform should be capable of deployment in water depths from 50 meters to 150 meters (around 160 feet to 500 feet) and survive significant wave heights of up to 15 meters (50 feet). A further requirement was for simple port logistics.

The design has a width under 70 meters (230 feet) and a draft under 10 meters (33 feet), making it compatible with most harbors, and does not require heavy crane vessels or dry docks for installation.

Finally, Saipem envisages that turbines could be fitted to the structure within the harbor and then towed out to sea even with significant wave heights of up to 3 meters (10 feet).

The oil and gas firm, best known for pipeline projects such as Nord Stream in Europe, claims the Hexafloat could outperform other floating foundation designs, including barges, semi-submersibles and spar buoys, on angular stability and structural weight.

Oil and gas firms circle floating offshore wind

Saipem’s foray into floating offshore wind follows moves by other oil and gas players to break into the nascent sector.

The Norwegian company Equinor, previously known as Statoil, leads the race for floating wind leadership with a spar-buoy platform that has already been deployed commercially in Scotland.

And Royal Dutch Shell this year announced a collaboration with German utility Innogy and technology developer Stiesdal Offshore Technologies to test a TetraSpar floating foundation concept off the Norwegian coast.

Both Shell and Saipem have also invested in airborne wind energy systems. Shell pumped an undisclosed sum into the former Alphabet startup Makani in February. Saipem followed suit last month with an investment in KiteGen Research, an Italian company.

Saipem declined to comment on the KiteGen deal, which was carried out through its Xsight high-value services arm.

“Saipem is continuously scouting the market for innovative and breakthrough technologies within the renewable energies and green technologies product line of its newly born Xsight division," said Francesco Balestrino,the division's product manager for renewables & green technologies. 

Other parts of the business are investigating markets including biofuels, PV, concentrated solar power and carbon capture, utilization and storage, he said.