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The Energy Technologies Institute (ETI) has taken a step towards building a £25 million, 6MW offshore wind floating platform after selecting the US-based Glosten Associates to carry out a front-end engineering design study of the structure.
Should the demonstrator be built, it will be installed at the Wave Hub grid-connected renewable test facility off Cornwall, and should be operational by the summer of 2016.
Andrew Scott, offshore wind programme manager at the ETI, said that floating platforms needed to be developed to enable wind operators to install their devices in deeper waters, which offered better wind conditions than existing shallow-water developments.
“Analysis has shown that when you get to 60 metres, moving to shallower foundations, rather than foundations fixed to the seabed, is likely to be cost-effective,” he said.
“Our project is targeting the creation of a floating platform for 60-100m water depths. We’ve commissioned Glosten Associates to carry out a front-end engineering design study for its PelaStar tension-leg platform, to be installed at the Wave Hub site off the north-west of Cornwall.
“Glosten will also carry out a sensitivity study, so that we understand the changes that might be required to apply its solution across a wide range of UK waters, not just the Wave Hub site.”
Bill Hurley, Glosten’s PelaStar director, said: “This is a bold step to greatly accelerate the development of floating offshore wind.
“Deep-water wind resources promise lower costs for energy and are waiting to be captured. The industry needs support of this nature to demonstrate the technology that will get us out there.”
Glosten said that PelaStar integrates proven tension-leg platform technology, widely used in the offshore oil and gas industry. The tendons incorporate a new material that is claimed to provide benefits over the more widely used steel pipe. The lower end of the tendon will connect to a component that can be rigidly connected to an anchor connector with a remotely operated vehicle-actuated pin. At the top of the tendon, the link attaches to a mushroom-shaped connector. The connector’s cap sits in a circular pocket in the hull’s tendon porch.
As part of the PelaStar design, high vertical load anchors are permanently set to resist the vertical loads that could otherwise pull them out. Four types of anchors are being considered: plate anchors; suction piles; driven piles in clay, sand, or silt; and drilled and grouted anchors in bedrock.
Plate anchors, for instance, are rectangular plates that are embedded in the sediments and rotated horizontally so that they resist uplift by the weight and cohesion of the soils above them. The plates are typically 15 to 30 m2 and are embedded 20 to 40m below the seabed. Plate anchors have high holding capacity-to-weight ratios, so the cost-to-performance ratio of an individual anchor is low.
Glosten said that plate anchors have been installed with capacities of more than 1 million lb (450 tonnes). The size, shape, and embedment depth depend on the soil classification, and the required anchor-holding capacity is a function of wind, wave, and current loads.
The £4 million front-end engineering design study will take about 12 months to complete. ETI said that should it proceed with the initiative, the full-scale demonstrator would be made by Harland and Wolff. The 6MW turbine will be supplied by Alstom.