Building Hywind Tampen

BY OLE KVADSHEIM, NORWEGIAN PETROLEUM MUSEUM

On 5 June 2022, the first of the 11 Hywind Tampen turbines was towed out to the field. The turbines rise 190 metres above the sea and are anchored to the seabed—at depths of up to 300 metres—using 19 suction anchors. The turbines were assembled in Gulen Industrial Harbour in Sløvåg in Sogn og Fjordane.

— Hywind Tampen is being assembled at the Wergeland base in Gulen. The finished turbines float in Fensfjorden before being towed out to the field. Photo: Ole Jørgen Bratland/Equinor

Plans for Hywind Tampen were first announced by Statoil at the ONS oil and energy exhibition in 2018. A few months later, in March 2019, the environmental impact assessment was submitted to the Ministry of Petroleum and Energy.

Project description

Hywind Tampen comprises 11 floating wind turbines installed at sea depths ranging from 260 to 300 metres. Positioned between the Snorre and Gullfaks fields, they provide renewable power to the offshore platforms, supplementing the gas turbines used on site.

Each turbine stands 190 metres above the sea surface and rests on a submerged concrete substructure extending 90 metres downward. The rotor blades have a diameter of 167 metres.

Equinor conducted design studies for substructures in both steel and concrete. The environmental impact assessment concluded that concrete was the preferred material—using the same design model as the Hywind Scotland turbines that had been deployed off the coast of Scotland a few years earlier. The decision was based on the fact that this concept had already been tested and was considered technically mature enough for use at Tampen.

The image shows the different components of a floating wind turbine.

Each turbine generates 8 MW. Six of them supply power to Snorre A, while five are connected to Gullfaks A. The turbines are linked through a circular grid system, which allows energy to be redistributed from Gullfaks to Snorre. This design enables flexibility as future power demand at Gullfaks is expected to decrease along with declining production.[REMOVE]

Fotnote: Equinor. (2019, mars). Hywind Tampen PL050 – PL057 – PL089 PUD del II – Konsekvensutredning (s. 30).

Construction

Construction of the various components took place at multiple locations across Norway and Europe.

The concrete foundations were built by Aker Solutions. The first 20 metres of each foundation were cast at Stord.

The first 20 metres of the concrete foundation were constructed in Stord. photo: Equinor (2023, August 23). Hywind Tampen A to Z

The structures were then towed to Dommersnes in Vindafjord, where casting continued vertically.

The concrete substructure’s first towing stage went from Stord to Vindafjord. photo: Equinor (2023, August 23). Hywind Tampen A to Z

The method used in this stage of the construction process is known from the Condeep era as “slipforming.” As the concrete structure grows taller, it is gradually lowered into the fjord. The construction technology for the substructures is based on the same principles used in building Condeeps. In total, about 32,000 cubic metres of concrete were used across all 11 platforms.

As the concrete structure rises, it is gradually lowered into the fjord. illustration: Equinor (2023, August 23). Hywind Tampen A to Z

This may seem like a vast amount of concrete, but it still represents only 13 percent of the volume used in the construction of the Troll A platform.[REMOVE]

Fotnote: Det ble brukt 245 000 kubikkmeter betong i Troll A.
Heidelberg Materials. (n.d.). Troll A. Hentet 9. oktober 2024 fra https://sement.heidelbergmaterials.no/no/Troll_A

The concrete element was then transported—along with other turbine components—to the Gulen industrial port in Sløvåg, where the assembly took place.

During this phase, the underwater structures were first moored to the quay.

The image shows the subsea structures of the 11 turbines. For the first time since Troll A (1995), concrete subsea structures were built for Norwegian offshore installations. photo: Johnny Engelsvoll, Equinor

Next, the towers were installed. Each tower was assembled from four segments stacked on top of each other. Then, the nacelle—which holds the rotor hub—and the three rotor blades were lifted into place using a land-based crane.

The rotor blades are being mounted on one of the Hywind turbines. The crane used for the installation is among the tallest in the world and has a lifting capacity of up to 5,000 tonnes. photo: Jan Arne Wold / Equinor

Towing and installation

Once the internal equipment had been installed, the turbines were towed to the field. The first turbine was ready for towing in June 2022. One by one, the turbines were moved to the field, 140 kilometres offshore.

One of the Hywind turbines is towed from Gulen to the field. photo: Equinor (2023, August 23). Hywind Tampen A to Z

Each turbine was anchored to the seabed using a total of 19 suction anchors and corresponding chains. These anchoring systems had already been pre-installed on the seafloor ahead of the turbines’ arrival.

The anchors are designed to be retrievable using remotely operated vehicles (ROVs) when the facility is eventually decommissioned.[REMOVE]

Fotnote: Equinor. (2019, mars). Hywind Tampen PL050 – PL057 – PL089 PUD del II – Konsekvensutredning (s. 32).

The first seven turbines were towed out during the summer of 2022. The remaining four followed in the summer of 2023. By the end of the summer, all 11 turbines were up and running.