TetraSpar towed inshore after five years of testing at METCentre

After nearly five years of continuous operation off the coast of Karmøy, the TetraSpar Demonstrator has been safely disconnected from its moorings at the Marine Energy Test Centre (METCentre) and towed inshore to Hanøytangen near Bergen.

The move marks the completion of a pioneering offshore test campaign that has delivered one of the floating wind industry's most comprehensive real-world datasets to date.

While many test projects focus primarily on power generation, TetraSpar’s five-year deployment has proven every stage of a floating turbine's lifecycle: from modular quayside assembly without welding, to towing, offshore hook-up, deepwater operation, and now offshore decommissioning.

A landmark operational record

Installed in 2021 at a water depth of 200 metres, the 3.6 MW Siemens Gamesa turbine on Stiesdal Offshore’s modular steel foundation operated in harsh North Sea weather conditions. Over its operational lifespan, the demonstrator achieved:

The offshore decommissioning campaign was managed by Global Maritime, with local subsea and marine service suppliers executing the offshore disconnection. As part of the campaign, the project team successfully lowered the dynamic export cable to wet storage at 210 metres water depth, clearing the berth for future demonstrator projects at METCentre.

Front-row seat for parliamentarians

In a timely coincidence during the ONS conference week, the Standing Committee on Energy and the Environment from the Norwegian Parliament (Energi- og miljøkomiteen) became the first official delegation to visit the test site immediately after TetraSpar was unhooked.

Travelling by boat from Stavanger up to Karmøy, the parliamentarians got a front-row seat to the final stage of the offshore operation: witnessing crews retrieving the very last anchor from the seabed.

With TetraSpar safely on its way to Hanøytangen, Zephyros — the world’s first floating wind turbine (originally installed as Hywind Demo in 2009) — now stands as the sole occupant off Karmøy. However, this solitude will be brief; the departure of TetraSpar frees up grid capacity and seabed space for the next wave of novel floating wind concepts preparing to deploy at METCentre.

From digital data to physical inspection

The floater is currently secured at temporary moorings at Hanøytangen, where engineers from Stiesdal Offshore and project co-owners RWE and TEPCO Renewable Power will perform detailed physical inspections of components that spent nearly five years submerged.

By comparing physical structural evidence, such as material fatigue, corrosion resistance, and hydrodynamic wear, against 40,000+ hours of continuous operational data, the partners aim to validate and refine their lifetime design assumptions.

A big thank you and congratulations to everyone involved in the TetraSpar project. It has been a pleasure working with a strong and dedicated team throughout these five years. There is a lot of experience and competence built through this project that can help put floating wind back on track. We look forward to the next chapter with TetraSub!

— Cecilia Girard-Vika, Director at METCentre

Scaling up: From TetraSpar to TetraSub

The learnings gathered off Karmøy are already feeding directly into the next generation of commercial floating foundations. Stiesdal Offshore is carrying the industrialised modular principles proven in TetraSpar forward into TetraSub, its foundation designed for 15+ MW turbines. TetraSub has already been selected for the 92.5 MW Pentland Floating Offshore Wind Farm project in Scotland.

For nearly five years, the TetraSpar Project has been generating data from a full-scale industrialised floating wind foundation in real North Sea conditions. Now, we and our co-owners RWE and TEPCO RP get something different: the chance to physically inspect it. Design assumptions will meet physical evidence across manufacturing, assembly, operation, and decommissioning. The knowledge gained will sharpen our understanding of how industrialised floating foundations are expected to behave over their lifetime, at a point where floating wind is moving towards large-scale commercial deployment.

— Stiesdal, in a LinkedIn post

For more on Semco Maritime's onshore decommissioning, see the last half of the article Refusing to wait: Norwegian Offshore Wind moves forward.