The floating world

The Scottish Government is extraordinarily active in the area of offshore wind energy. The waters off Scotland contain two sites that claim to be the world’s first floating turbine array. In recent months, the government has given planning permission for a floating offshore wind farm to be installed in the North Sea off the coast of Peterhead. It has also granted a licence for the Norwegian energy firm Statoil’s Hywind commercial demonstration scheme of five turbines. These will be attached to the seabed by a three-point mooring spread and anchoring system, making them easy to install in deepwater. According to the company, final commissioning could take place in 2017.

In March 2017, the government also gave the go-ahead for a proposed eight-turbine floating offshore wind farm near Aberdeen. The £250 million ($318 million) Kincardine development has a permitted generating capacity of up to 50MW. It is being developed by a joint venture between Atkins and Pilot Offshore Renewables. Eight Senvion 6.2M126 turbines will be installed 15km south-east of Aberdeen and tethered to the sea bed using Cobra’s Semi-Spar concrete substructure technology.

New projects

In 2016, Swedish engineering company Hexicon submitted an application to Marine Scotland to construct a demonstration floating offshore wind project at a site along the north coast of Scotland, about five miles off Dounreay, near Caithness. In February 2017, the planning committee approved the application for the project, known as Dounreay Tri.

The 10MW twin turbine project will be developed by Hexicon in association with Atkins and will be located in deeper waters off the north-west coast of Scotland.

Marcus Thor, Dounreay Tri’s project director, says, “This demonstration facility that will be built and operated in Scotland opens up the possibility for a significant increase in offshore wind generation and associated supply chain benefits.”

Atkins has worked with Hexicon since 2015 to design what it describes as the world’s first multiturbine offshore wind floating platform. The project is set to be operational by mid-2018. It will consist of a single semisubmersible platform and two wind turbines with a total capacity of 8–12MW based approximately 6km offshore. A single export cable and the associated onshore electrical infrastructure will connect to the existing substation at Dounreay.

Data emphasis

The Energy Technologies Institute recommends that more emphasis is placed on floating foundations to access the best offshore wind resources in the UK and help bring costs down further.

“Floating platform solutions should be further derisked; at the moment, investors and developers still favour fixed-foundation solutions,” it says. “Industry needs to continue to increase its practical experience in offshore wind through further deployment and learn from this to contain operational costs. For waters less than 30m deep, ETI analysis points to fixed foundations offering the prime solution from a costeffective perspective, but at more than 50m deep, floating foundations would provide the lowest cost solutions.”

This assessment comes as the institute releases data from its research into offshore wind in the UK, including a front-end engineering design study into its floating-platform demonstration project. The study centred on a tension-leg platform design, in partnership with an Alstom 150-6MW Haliade turbine.

This is a project using PelaStar technology, which has been under development by Glosten since 2006. Glosten conceived the PelaStar system as a way of reducing capital costs while accessing deepwater sites with superior wind resources, and also a way to enable new geographic markets. Various platform types were considered and the tensionleg platform emerged as the clear technical solution due to its potential for low structural weight, quayside assembly, and suitability for sites with 50–200m of water depth and more.