Constructing the world’s largest, furthest-from-shore offshore windfarm is a massive challenge, but solutions that Ørsted has adopted to build it will help provide answers to challenges on even larger projects
Tensions between pushing the boundaries of technology and innovation while managing risk and safety pose challenges in the development of any offshore windfarm, but as they are built further from shore, using ever-larger turbines, in ever more challenging conditions, so engineering and technical challenges are growing.
So too are the industrial challenges of building massive projects – issues with suppliers could potentially hold up a project and cost millions of pounds in delays, so new manufacturing solutions are needed that can cope with the sheer scale of projects.
With 174 Siemens Gamesa turbines, the 1.2 GW Hornsea Project One offshore windfarm in the North Sea will be the biggest in the world when it is completed in 2020. Even this massive scheme will be superseded in size by the next in the Hornsea Zone, Hornsea Project Two. Together, Hornsea One and Two will provide 2.6 GW of offshore wind capacity.
To get an idea about how Hornsea Project One is being built, what the challenges are and how they are being addressed, OWJ conducted an exclusive interview with Ørsted’s project manager for Hornsea One, Duncan Clark.
At the time of writing in early May, offshore construction had been under way for nearly five months. The jackets for all four offshore substations had been installed and the first section of offshore cable out of 900 km had been laid.
More than 100 km from shore, covering an area of about 407 km2, Hornsea Project One is further offshore than any other windfarm, a fact Mr Clark said presented numerous challenges but has seen the industrialisation of offshore wind taken to a new level.
“The principal challenges on Hornsea One arise from its sheer scale and because it is so far from shore,” Mr Clark said. This means that conventional solutions to logistic challenges – such as transporting workers offshore on a daily basis – would not work.
“You can’t shuttle more than 100 people backwards and forwards over 100 km every day,” said Mr Clarke, “not like you can on a nearshore windfarm. We’ve had to adopt different logistic solutions, such as using helicopters when transfers are required and having people live offshore while construction is under way, on jack-up accommodation vessels.” A similar approach will be needed once the windfarm is in operation and the operations and maintenance phase starts.
Offshore workers are accommodated on the jack-ups for two weeks at a time and have a specially-developed access system to transfer them from the jack-ups to the substations as they are being built.
One of the jack-ups, contracted from Gulf Marine Services (GMS), is already supporting work on the substations; the second is due to be mobilised shortly. Both have an innovative boat landing system developed by Osbit that is integral to enabling work crews to remain offshore, rather than making daily trips to and from shore. The system will facilitate up to 50 crew transfers each day and is raised and lowered into position using the jack-up’s crane. Hornsea One’s four offshore substations include the world’s first reactive compensation substation, an essential part of transmitting the electricity produced by the offshore windfarm to shore over great distances, enabling the high voltage AC system to work with cable lengths longer than those previously used for offshore wind.
To meet the manufacturing timescale for the huge project, Ørsted is also working with the UK supply chain and bringing new players into the sector that have not worked in offshore wind before, increasing the level of work of those already in the supply chain. “The project is a great story in terms of engineering and for those interested in it from a supply chain perspective,” Mr Clark said.
“Apart from working with companies that are new to supply chain, we’ve also had to split the manufacturing work scope to ensure timely deliveries,” he explained. “On a project of this scale and complexity, there are no lucky escapes if something goes wrong with a supplier.”
Among the companies that are new to the offshore wind industry who have come on board Hornsea One is Wilton Engineering on Teeside, which, along with its own supply chain, has become involved in manufacturing the transition pieces for the windfarm.
“For all of the main engineering scopes, whereas on a smaller project we might work with a single supplier, the size of Hornsea One means that we are working two, three sometimes four suppliers in order to be able to maintain the pace of delivery required,” Mr Clark told OWJ. “It is testament to the fact that the industrialisation of the supply chain has been keeping up with the growing size of sites and turbines, including installation of cables, turbines and other components using bigger vessels,” he said.
Hornsea One has seen other offshore contractors that are new to offshore wind assume key roles. Among them is Saipem, the well-known offshore oil and gas contractor, whose crane vessel Saipem 7000 is installing the offshore substations. As of early May, the vessel had installed all four jackets for the substations with three topsides to go.
Flexibility is essential on a project this size, as is access to suitable vessels, when required. Here Ørsted had a large slice of luck when it encountered a problem with a cable lay vessel due to undertake much of the work on the project.
Tideway, a subsidiary of the Belgian dredging, environmental and marine engineering group DEME, was awarded a design-and-build contract for the export cable installation for Hornsea Project One and was due to undertake the work using its newbuild dynamic positioning Class 3 vessel Living Stone.
The cable lay vessel was built by Spanish shipyard LaNaval with delivery planned for April 2017 but problems at the yard mean that it has yet to enter service. As a result, said Mr Clark, Ørsted and Tideway needed to quickly find another vessel capable of undertaking the work.
It did so in Norwegian owner Ocean Yield, with which Tideway concluded a timecharter contract for the vessel Lewek Connector. Tideway will carry out the first section of the cable lay using Lewek Connector, with Living Stone due to join the project at a later date.
Lewek Connector has two large turntables with capacity to hold up to 6,000-tonne cables and has laid subsea cables since 2012 in a range of water depths. For this particular job, the lay system on the vessel has been replaced with a bespoke back deck cable lay spread designed and installed by Tideway for the project.
Mr Clark said fitting Lewek Connector with the bespoke kit was a way of ensuring the project goes according to plan. “It’s well-known in the industry that cablelay is a complex process and is rather weather-sensitive. Previous projects have been held up because of problems with cablelay. It can be expensive if something doesn’t go according to plan. Lewek Connector is a very capable vessel, but we wanted the equipment it used to be just right. We wanted to make sure that the ship had just the right tools on board to undertake the project and could undertake the job within its technical constraints, so it was modified.”
So far, said Mr Clark, the export cable work using the ship has gone as planned, and as it continues so array cabling installation work will get under way, more and more of the transition pieces will be installed and the substations completed. And that’s just the offshore aspects of the project.