Floating Offshore Wind Foundations unlock new renewable energy potential. Average wind speeds are higher and more consistent further from shore and around 80% of Europe’s offshore wind resources is located in waters of more than 60 meter depth, where bottom-fixed offshore wind structures are not economically attractive. This means floating offshore wind farms can produce more energy throughout the year and have high capacity factors. Some of the largest potential markets, such as Japan and the United States, possess few shallow-water sites suitable for offshore wind development. Floating foundations could be game changers for power generation from deeper waters as they eliminate the depth constraint. Floating Offshore Wind Structures also open new markets Europe (France, Norway, Spain and Portugal) for the offshore wind energy industry and allows for the harnessing of great wind resources in shallower waters (as low as 30m) where the seabed quality makes bottom fixed offshore wind economically unviable.

Currently, offshore wind farms have been using three main types of deep offshore foundations, adapted from the offshore oil and gas industry:

Spar-Buoy: a very large cylindrical buoy stabilises the wind turbine using ballast. The centre of gravity is much lower in the water than the centre of buoyancy. Whereas the lower parts of the structure are heavy, the upper parts are usually empty elements near the surface, raising the centre of buoyancy. The Hywind concept consist of this slender, ballast-stabilised cylinder structure.

Tension Leg Platform: a very buoyant structure is semi submerged. Tension mooring lines are attached to it and anchored on the seabed to add buoyancy and stability.

Semi-Submersible: combining the main principles of the two previous designs, a semi submerged structure is to reach the necessary stability. WindFloat uses this technology.

30+ MW Projects in Europe:

Kincardine Scotland, Semi-Sub Foundation

A Spanish joint venture between shipbuilding company Navantia and tower and foundations specialist Windar (JV Navantia-Windar) will deliver the floating foundations for the world's largest floating array which will be commissioned in 2020. The joint venture will fabricate five WindFloat semi-submersible platforms, designed by Principle Power, for the 50 MWKincardine array off the north-east coast of Scotland, UK.

Project developer Kincardine Offshore Wind Limited (KOWL), which is majority-owned by Spanish construction company Cobra Wind International, states that five 9.5MW MHI Vestas turbines will be mounted on the platforms (GrupoCobra, 2019). MHI Vestas confirms that the turbines will be installed in spring 2020 and will include a 10-year service and maintenance agreement (MHIVestas, 2019).

“We are exceptionally proud that the world’s largest floating offshore wind park will feature the V164-9.5 MW turbine.” Said MHI Vestas Chief Executive Officer, Phillipe Kavafyan. “Bringing our technology and experience to Kincardine in Scotland advances our leadership in floating offshore wind and confirms our long-term commitment to commercial scale for floating offshore wind projects in the future.”

Windar started the construction of the foundations at its facilities in Avilés (Northern Spain) in May 2019. The assembly of the foundations will be carried out at the Navantia yard in Fene (Spain) where the construction of the unit for WFA will be carried out. The construction is planned to continue until April 2020 (Windar, 2019).

Navantia stated that about 1,250,000 man-hours are expected for the production process, using approximately 15,000 tonnes of steel. JV Navantia-Windar has already installed five spar-type units at Equinor’s Hywind project in Scotland, and one semi-submersible design at Windplus’ Windfloat Atlantic project off of Portugal (Navania, 2019).

The wind turbines are installed from the quayside directly onto the platform to reduce the time and risk of operations offshore.

The Kincardine demonstration achieved first power in October 2018, when a 2 MW Vestas turbine was commissioned at the site (GrupoCobra, 2019).

Specifications of the Kincardine Floating Offshore Wind

Developer: Kincardine Offshore Wind, Ltd (KOWL). Majority owned by the Cobra Group

EPC Contractor: Cobra Wind International Limited (CWIL).

Installation Date: Spring 2020

Turbines: 5 x V164-9.525 MW + 1 V80-2.0 MW

Blade tip height: 190 meters

Foundation: WindFloat (floating, semi-submersible)

Foundation designer: Principle Power, Inc.

Project Capacity: 49.625 MW

Location: Aberdeen Bay, Scotland

Distance from Shore: 15 km

Sea Depth: 60-80 meters

Nominal Voltage: 33 kV

# of homes powered annually: 35,000

Expected life: 25 years

Noteworthy fact: Most powerful wind turbines operating on a floating foundation

Hywind Scotland, Spar-Buoy Foundation

Equinor and partner Masdar invested NOK 2 billion to realise Hywind Scotland, achieving a 60—70% cost reduction compared with the Hywind Demo project in Norway. Hywind Scotland is world’s first operational floating wind farm. The 30 MW Hywind Scotland pilot park demonstrates the feasibility of future commercial floating wind farms that could be ten times larger. Hywind Scotland started producing electricity in October 2017 (Equinor, 2018). Hywind is a unique offshore wind technology, consisting of a mix of available technology and new patents developed and owned by Equinor. Hywind uses a Spar-buoy design, which is a cylinder with low water plane area, ballasted to keep the centre of gravity below the centre of buoyancy. The foundation is kept in position by catenary or taut spread mooring lines with drag or suction anchors. The Spar-Buoy is equipped with a boat landing, a passage for the submarine power cable (cable entry hole) an airtight platform to prevent water inlet, connection for the ballast pump(s) and anodes (highly active metals that are used to prevent a less active surface from corroding). Studies from EQUINOR (2017) show that their Hywind turbine (spar-buoy design) can be used up to 800m of debt.

The Spar-Buoy is launched into the water and towed to a nearby location where the Spar-Buoy foundation can be upended and prepared for the turbine installation.

The wind turbines are completely assembled onshore to reduce the time and risk of operations offshore. and then installed by single lift using a floating crane (sheerleg) or installation vessel.

Specifications of the Kincardine Floating Offshore Wind

The wind farm will power around 22,000 households.

The farm consists of five 6 MW turbines with a total installed capacity of 30 MW, and a transmission voltage of 33 kV.

The rotor diameter is 154 m and overall height is 253 m.

The pilot farm will cover around 4 square kilometers in water depths varying between 95—129 meters.

The average wind speed in this area of the North Sea is around 10 meters per second, while the average wave height is 1.8 meters.

The export cable length to shore is 30 km.

Hywind Tampen

Hywind Tampen will be developed to supply power to offshore oil and gas platforms in the Norwegian sector of the North Sea and will become the world’s first project to use wind turbines for electrification of oil and gas installations, expected to be operational in 2022. Reduction of CO2 emissions from the five oil and gas platforms at the Snorre and Gullfaks fields is estimated at more than 200,000 tonnes per year. According to Equinor, the offshore windfarm will feature 11 Hywind Spar-Buoy foundations and 11 8 MW wind turbines that will have the capacity to generate 88 MW of electricity. This will be sufficient to meet 35% of the annual power demand of five platforms.

Hywind Tampen project director Olav-Bernt Haga said: “The Hywind Tampen project will contribute to further developing floating offshore wind technology and reducing the costs of future floating offshore windfarms, offering new industrial opportunities for Norway, the licences and Norwegian supplier industry in a growing global offshore wind market.”

The project will also receive Nkr566m ($62.9m) as investment grant from the Business Sector’s NOx Fund.

The Gullfaks partners are Equinor Energy, Petoro and OMV (Norge), and Snorre partners are Equinor Energy, Petoro, ExxonMobil Exploration and Production Norway, Idemitsu Petroleum Norge, DEA Norge and Vår Energi.

References:

Equinor (2017) Hywind Scotland Begins Production. Available at: https://www.equinor.com/en/news/worlds-first-floating-wind-farm-started-production.html

Equinor (2018) Hywind. Available at: https://www.equinor.com/en/what-we-do/hywind-where-the-wind-takes-us.html

GrupoCobra (2019) Kincardine Offshore Floating Wind Farm. Available at: http://www.grupocobra.com/en/proyecto/kincardine-offshore-floating-wind-farm/

MHIVestas (2019) MHI Vestas To Supply Five V164-9.5 MW Turbines for Kincardine Floating Offshore Wind Park in Scotland. Available at: http://www.mhivestasoffshore.com/mhi-vestas-to-supply-five-v164-9-5-mw-turbines-for-kincardine-floating-offshore-wind-park-in-scotland/

Navantia (2019) Joint Venture Navantia-Windar are awarded the construction of 5 floating foundations for offshore wind farm. Available at: https://www.navantia.es/en/news/press-releases/joint-venture-navantia-windar-are-awarded-the-construction-of-5-floating-foundations-for-offshore-wind-farm/

Windar (2019) JV Navantia-Windar won a contract for Kincardine Project. Available at: http://www.windar-renovables.es/news-and-press-detail/en/135