Marine Renewables

US offshore wind studies under way

The US Department of Energy has awarded GL Garrad Hassan two grants worth a total of $700,000 to fund studies that will help identify optimal strategies for the installation, operation and maintenance of offshore wind farms and to assess the readiness of US ports to meet the burgeoning industry's needs.

The grants are part of a wider Obama administration initiative that has awarded $43 million to promote offshore wind technology in the US.

The GL Garrad Hassan ports assessment will examine the current and future capacity of US ports to meet the offshore wind industry's requirements for assembly, construction and operational staging for projects. ‘Port infrastructure will have to be dramatically expanded for renewable energy generation policy targets to be met,' the company said. ‘The outcomes generated by this study will help Federal and State policy-makers and port authorities take effective action to maximize the economic potential of ports in the offshore value chain.'

The second study will look at optimal approaches to installation and operation of offshore wind farms, and will provide detailed cost assessments that can be used to understand and mitigate financial risk. Noting the number of European offshore wind projects that suffered construction delays and cost overruns, the company said the new study would help the US industry avoid such pitfalls.

The consultancy will also provide results of the studies to stakeholders in the form of analysis tools for individual projects and will conduct stakeholder workshops during the final stages of each study.

Belgian cable connections

A total of 57km of high-voltage subsea power export cables are to be supplied by Nexans for Belgium's Northwind offshore wind farm under a E50 million contract. The company's Halden plant in Norway will supply 14km of cable to connect Northwind, formerly known as Eldepasco, to phase two of another Belgian wind farm development, Belwind, and another 43km of cable to transfer 381MW of power from both wind farms to an onshore grid connection at Zeebrugge.

The Northwind project will comprise 72 wind turbines with a total of 216MW installed capacity.

Nexans' workscope includes the design, type-testing and supply of XLPE subsea cables along with mechanical and electrical accessories: onshore transition joints and accessories for the two platforms, including hang-off and gas insulated switchgear terminations and four repair joints. The 14km cable section will have three copper cores each with a cross-section of 400mm2. Most of the 43km, 245kV connection will contain three 1000mm2 copper cores; a 4km section that will run under a sea channel subject to periodic dredging will be buried 9m beneath the seabed and will have a cross-section of 1200mm2 and an outer diameter of 265mm.

Pile relief drilling

A custom-built LD5000 pile top reverse circulation drilling rig has been delivered to Birkenhead in the UK, where LDD will use it to provide critical pile relief drilling for the installation of up to 160 wind turbine foundations forming part of the Gwynt y Môr wind farm development in Liverpool Bay.

‘Developing the LD5000 really put our engineering expertise and creative abilities to the test,' said Andy Seager, VP operations for LDD, an Acteon company. The drilling equipment spread, which weighs around 400t and is over 17m high, is capable of drilling up to 8m in diameter. It has the ability to produce 1100kNm of continuous torque and 500t of pull-back.

Most of Gwynt y Môr's foundation monopiles are expected to be driven to target depth with a MHU 1900S submersible hydraulic hammer from LDD sister company Menck. However, whenever hard geology prevents the monopile from reaching its installation depth the LD5000 will be transferred from the installation vessel, to replace the hammer and drill out material inside the monopile and beyond. Once the relief drilling has been completed, the hammer will replace the LD5000 and the drive-drill-drive sequence will be completed by driving the monopile to its target depth.

Because the wind turbine monopiles are tapered – 4.6m diameter at the top and between 4.7m and 6.0m at the bottom – they pose a challenge for the pile relief drilling. LDD designed its rig with an underreaming drill bit, so that it can pass through the neck of the monopole and drill a range of rock socket diameters, from a standard 4.6m diameter up to 6.0m.

The LD5000 makes it possible to fine-tune the diameter and depth of the rock socket in direct correlation with the exact diameter of the monopole, explained Seager. ‘This means that installation of the monopile will be fully optimised. It also ensures that when the monopile is eventually driven to target depth, the external wall of the monopile will be in direct contact with the surrounding bedrock, providing the wind turbine generator with longterm stability.

LDD will provide pile relief drilling services for two years throughout the construction of Gwynt y Môr.

Twin-bladed turbine tests

Tests of a new two-bladed offshore wind turbine developed by renewable energy company 2-B Energy could be conducted off the coast of Scotland by late 2014 as a result of collaboration between the Dutch company and Scottish Enterprise. The two have teamed up to commercialize the technology, which 2-B Energy says could cut the cost of offshore wind by 45%.

According to Scottish Enterprise, the 2-B design ‘bucks the trend toward the more conventional threebladed horizontal axis onshore wind technology currently being deployed offshore' and could significantly reduce the number of components needed over the life of the turbine, which could lower maintenance and operation costs. The concept is compatible with the 6MW power generation standard and has a 140m rotor diameter but differs from conventional turbines by using a two-bladed rotor on a full lattice structure that reaches the seabed.

The Aberdeen-based Scottish European Green Energy Centre has backed 2-B's application for funding through the EU framework Programme 7 to develop the technology and to demonstrate it in Scotland. Plans call for the project to be developed at Scottish Energy's Fife Energy Park in Methil. Initial plans for a single unit nearshore have been scaled up to two offshore turbines, which will form the basis of a hub for various interests in the Scottish offshore wind industry.

The agency did not specify the amount of funding 2-B is seeking to develop the project. Scottish European Green Energy Centre CEO Chris Brondson said the effort to secure funding for the ‘multi-million Euro flagship demonstration project for this technology' had been in the works over the past year.

‘The technology approach maximises the potential for cost reduction from the outset, whilst minimising technology risk through using existing, proven components that have already been operating and financed in the market for several years,' Brondson said.

ACCESS ADVANCE: Osbit Power (OP), Siemens Wind Power and Statoil confirmed recently that they had successfully completed offshore trials of OP's innovative offshore wind turbine access system, MaXccess. The trials were conducted at Statoil's Hywind pilot floating offshore wind turbine facility off Norway using the Fred Olsen wind farm service vessel Bayard 3. During nine days of offshore operations, over 100 connections were made, with MaXccess being clamped to the turbine buffer tube for over 12 hours in total, during which time 36 personnel transfers were made. Safe transfer took place in significant wave heights ranging from 1.2m up to 1.9m.