Stiesdal Starts Producing First TetraSub Floating Wind Foundation

July 7, 2025, by Adrijana Buljan

Norwegian energy technology developer Stiesdal has started production of the first TetraSub floating foundation, the semi-submersible variant of the company’s Tetra concept, which it says is best suited for water depths ranging from 50 to 200 metres.

Stiesdal has marked four years since its first full-scale floating wind turbine, the TetraSpar Demonstrator, was installed at the METCentre test site off the island of Karmøy near Stavanger.

TetraSpar Floating Wind Platform Installed Offshore Norway

Technology

The 4 MW prototype was commissioned at the end of 2021 and has, according to Stiesdal, delivered very solid operational data and proven the potential of the company’s modular approach.

In May last year, Stiesdal said the TetraSpar Demonstrator recorded an availability of 97 per cent and 98.3 per cent in the first two years of operation, respectively. In 2024, the availability increased to 99.5 per cent with a capacity factor of almost 63 per cent, according to the company.

TetraSpar Demonstrator Floating Wind Turbine Hits 63 Pct Capacity Factor in Norway

Floating Wind

In a social media post on 7 July, Stiesdal said the demo turbine’s availability was at 99.3 per cent in the latest reporting year.

Marking four years since its TetraSpar floating wind foundation was installed, Stiesdal also revealed the company had started work on its first semi-submersible variant of the Tetra foundation.

“Today, we’re happy to share the first glimpses of what comes next: TetraSub, our semi-submersible floating foundation, now in production. Designed for the world’s largest offshore turbines”, the company said via social media.

Stiesdal received DNV’s Statement of Feasibility for its semi-submersible floating wind foundation in 2021, and the following year, Pentland Floating Offshore Wind Farm (PFOWF) consortium selected TetraSub as the floating foundation technology for the 100 MW Pentland floating offshore wind farm.

According to the Norwegian floating wind technology developer, the largest part of the floating offshore wind market until 2030 will be in relatively shallow water, with depths in the range of 50-200 meters.

While its TetraSpar foundation is suited for water depths of 120 metres and above, TetraSub is a response to the market that is expected to initially evolve as an extension of the fixed-bottom offshore wind market, applying floating technologies to stretch offshore wind’s feasibility beyond the typical fixed-bottom maximum depth of 50-60 metres, according to Stiesdal.