Will it float?

Floating offshore wind projects are gaining momentum in Europe and elsewhere, including Japan. But, the concepts on offer still vary. Elaine Maslin reports.

Hywind schematic. Images from Statoil.

The premise is that, as wind energy builds out in shallower waters, developers will look to deeper waters to build offshore wind farms.

In some areas, such as Japan, where renewable energies are being sought following the Fukushima nuclear disaster, floating facilities are in fact the only option for offshore wind, as the continental shelf fast plummets into deepwater.

For the likes of Statoil, floating wind technologies offer the potential to provide power in remote areas or for oil and gas facilities.

But, floating wind could also be put into direct competition with fixed facilities, where opportunities to reduce costs, including around seabed preparation, could bottom out, or so the thinking goes.

“The potential for cost reduction on fixed structures is limited and where floating gets attractive,” says Cian Conrow, sector lead, wind, at the Offshore Renewable Energy (ORE) Catapult, a UK-based technology and innovation research center, at the All Energy conference in Glasgow, Scotland, this May.

The ORE Catapult is partner in a collaboration project, LIFES50+, led by Norway’s Marintek, involving 12 partners and US$8.25 million (€7.3 million) in European Union funding. It started in 2015 and will run for 40 months with a focus on proving technologies for floating substructures for 10MW wind turbines in >50m water depth. The partners included Spain’s Iberdrola, DNV GL, and Danish engineers Ramboll.

It could take time, however. A report written by DNV GL for Dutch innovation outfit TKI WindOp Zee in November 2015 said the then-current cost of floating wind solutions was estimated to be about 60% higher than bottom fixed solutions. “If floating is to become competitive it must demonstrate significant cost reduction, especially in the support structure, installation, moorings and anchors,” the report says.

Yet, many think it’s possible. According to the Energy Technologies Institute (ETI) in the UK, floating wind has the potential to have a levelized cost of energy (a metric on which the industry is measured) of less than $122 (£85)/MWh by the mid-2020s, in waters deeper than 50m (business consultancy EY recently said the same for offshore wind in general could read $101 (€90)/MWh by 2030). The ETI developed a floating design based on a tension leg platform.

Still, Una Brosnan, growth manager, offshore wind, at engineering firm Atkins, thinks there’s an opportunity, not least thanks to the potential market, at some 4000GW floating wind potential in Europe, 2450GW in the US and 500GW in Japan, she told All Energy.

Leif Delp, project director for Statoil’s Hywind floating wind park, told All Energy that the company’s key markets are Japan, California, Norway, for powering oil and gas facilities, and also Scotland and France. Hywind, off Scotland, is set to lead the race to deploy floating offshore wind.

Norman Pioneer tows the first Hywind device.

Hywind – in construction

The Hywind development is a 30MW park covering 4sq km and comprising five, 6MW floating wind turbines in up to 100m water depth. They will face relatively mild 1.8m mean wave heights, and 10.1m/sec average wind, off the coast of Aberdeenshire, Scotland. A 30km cable will connect the park to shore.

The project started as a concept in 2001, Delp says, during two engineers’ lunch break at the Hydro offices in Oslo and went on to see a one-turbine pilot offshore Norway, operating since 2009.

Hywind, above and beneath the waves, 3D illustration.

It uses a standard Siemens offshore wind turbines supported on a customized steel ballasted spar structure, moored using three mooring lines, connected to suction anchors, and incorporating a patented active motion controller, to reduce fatigue, as well as a bridle system. Capacity on the first pilot has been 41%, Delp says. The structure is 14.4m in diameter and 280m-long in total, with 170m of it above sea level, resulting in 11,000-tonne total displacement. “It is like putting the London Eye on top of [the tower housing] Big Ben [the bell inside the tower],” Delp says.

Some 15 main contractors are on the project, from around Europe. These include Navantia, at Ferrol, Spain, which is fabricating the substructures. Vicinay, also in Spain, is producing the mooring chains. The nacelle towers are being fabricated in Bilbao, Spain. Saipem will carry out the mating of the towers and nacelles, in Norway, using its S7000 heavy lift vessel. Isleburn is currently fabricating the suction anchors at Invergordon, Scotland. Balfour is responsible for electrical integration, Aluwind will do the tower internals, and Technip will do the marine operations, with Subsea 7 installing the electrical subsea cables from Nexans, which is due to start manufacturing the cables in Halden, Norway, early next year.

The project is on schedule for startup in Q4 2017, Delp says, following final commissioning in Q3-4 2017, offshore installation in Q2 2017, and offshore cable installation Q3 2017.

A future addition to the Hywind Scotland project is due to be Statoil’s latest concept, Batwind – battery storage for offshore wind. Batwind is being developed in co-operation with Scottish universities and suppliers. A final investment decision on a 1MW Lithium battery is due to be made in Q2 2017, with installation potentially in 2018.

In another project involving Statoil, with partners including Nexen, ExxonMobil, Eni, and VNG Norge, DNV GL has been looking at how floating offshore turbines could help power subsea equipment, in particular water injection systems, including pumps and basic water treatment. The project recently completed a year-long Phase 1 feasibility study, which DNV GL said had positive results and could result in standalone systems. The next phase is to prove it and do a demonstration.

Hywind in comparison to major landmarks.

Approval in Principal

Engineers, who previously worked at oil majors Shell and ExxonMobil, are behind Principal Power’s WindFloat, the project involving EDP, Spain’s Repsol, and Portugal Ventures.

WindFloat, based in California, has two projects near-term on its radar, its 3-4, 6-8MW turbine 25MW Atlantic project, planned for installation in 2018 at a site in 100m water depth, 20km offshore Portugal. Following that, it is looking at a project, with 5-8 turbines totaling about 48MW, in Scottish waters. The Atlantic project is supported by Engie, Repsol, Chiyoda, Mitsubishi, and EDP Renewables. Japan, France, and the state of Oregon, on the US’ west coast, are also in the firm’s sights.

WindFloat’s concept, the second generation of which recently gained approval in principal from classification firm Bureau Veritas, is a three-column semisubmersible structure, which heave plates on the bottom of each column for stability, alongside a hull-trim system, using active ballasting. It could take different standard offshore wind turbines.

It would be moored using drag embedded anchors – similar to drilling rig mooring – and could be installed using a tug and an anchor handler, said Joshua Weinstein, business development and operations, Principle Power, at All Energy.

Since 2011, the firm has had a 2MW full scale pilot operating 5km offshore northern Portugal, which Weinstein says has exceeded expectations, producing 16GWh of energy. In the future, the firm wants to house 5-8MW turbines and future 10MW size turbines.

Multitasking

Man with hi-vis gear. Photo by Helge Hansen/Statoil.

Danish firm Floating Power Plant has laid claim to having the world’s only “proven combined floating wind and wave device,” incorporating 5MW of wind and 2.6MW of wave power, using wave energy absorbers on a rocker arm.

The firm’s device sits on a semisubmersible cruciform shape structure, the stability of which it says is aided by the wave energy absorbers. The rocker arms sit in a channel, to enable control of the hydrodynamics, and they use double concave floats, instead of wedges. The wave energy absorbers also create a sheltered area for access to the platform.

A half scale prototype, the 37m-wide, 320-tonne P37, has spent around two years in testing offshore Denmark, including supplying compliant wave and wind powered electricity to the grid.

The firm’s P80 commercial scale device, for sites above 45m water depth, will have a single turbine, up to 5MW, and up to 2.6km wave power, from four absorbers. It will be moored using disconnectable turret technology, to enable it to weather vane to the wind and allow a route for the export cable.

The firm is eyeing possible projects at Dounraey, in the north of Scotland, and off Pembrokeshire, Wales. Both are undergoing screening with an unnamed development partner. The firm wants to start with a P80 demonstrator, then built out a 7.8MW pilot park, then a 30MW array, and ultimately a 200MW park.

Floating Power Plant has also been picked as a preferred technology partners on an offshore wind park project being developed by THV Mermaid, a consortium, off Belgium, which was consented on the basis of including up to 20MW of wave power. This would be 50km from shore in 42m water depth and using a P60 unit, said Chris McConville, the firm’s UK business developer, at All Energy.

Out of the box

Spain’s Saitec Engineering, meanwhile, has developed something a bit different – the Sath (swinging around twin hull) concept. It has a substructure based on two large, horizontally orientated, side by side, concrete cylinders, which are ovoidal in cross section to reduce compression stresses, on a pitch and roll plate, to reduce pitch and roll. Luis Gonzalez-Pinto, Saitec’s head of renewable energy, told All Energy that the Sath would be on a single point mooring system to enable it to weather vane into the wind, with an electrical swivel for the power export.

Saitec have trailed a scale model in a wave tank facility at the University of Cantabria, Spain. It had maximum oscillating angles of ±3 degrees, Gonzalez-Pinto says.

Earlier this year Marine Energy Engineering Solutions (MEES) and Doris Group’s ODE subsidiary revealed a plan they had developed for a floating articulated wind column for deepwater areas for up to 8MW turbines. It is based on the concrete articulated column technology developed for the Maureen platform in the North Sea, which was decommissioning in 2001.

The pair think nearshore, floating solutions could reduce costs by eliminating the need for offshore transmission stations, reduce cable lengths and do away with a lot of seabed preparation work.

Meanwhile, China’s Fujian Mindong Electric Power Corp. is investing in the development of a 48MW floating wind farm in Fujian province. It would involve 24, 2MW turbines and could start construction in 2018.

These are just some of the projects in the market, with many more technology offerings in Europe and devices being trialed offshore Japan (OE: July 2014). While a clear winning design is not yet there, one thing is for sure, there’re no end of ideas for one.