IN DEPTH: Floating forwards in wind

Europe is planting its flag on the floating wind sector with its largest-ever deep-water turbine demonstrator.

The €36m ($48.7m) pilot aims to have two distinct prototypes riding the swell off Spain by 2015.

FloatGen, an EU-funded consortium, expects to have engineering wrapped up this year on the concepts:

  • a 2MW unit developed around Gamesa’s G8X turbine mounted on a “surface floating” concrete platform designed by France’s Ideol;
  • and a 3MW prototype based on an Acciona AW-3000, with a semi-submersible to be designed by Spanish shipbuilder Navantia and offshore construction specialist Olav Olsen of Norway.

The four-year project is on the fast track. The world’s gustiest offshore region, off the UK, will need 6GWh per year from floaters to reach a targeted capacity of more than 245GW by 2050, harnessing 70% of the country’s deep-water wind resource.

Progress of the offshore wind industry has been slowed by the economic crisis, because developers are making much smaller advances, to manage technology risk, says FloatGen co-ordinator Mauro Villanueva-Monzón, below, technology development director at Spanish turbine maker Gamesa, which is leading the consortium.

“There have been other European Commission projects that look at specific floater designs as machines, as products, but nothing like this, where there will two systems being demonstrated holistically with a benchmark approach to the technologies,” he adds.

“I feel this is a wise strategy because it promotes healthy competition between the concepts. Also, it is a kind of ‘belt and braces’ approach... if one concept should fail, there will still be a second concept going forward.”

The Ideol

webGamesa-MauroVillanueva_2.jpg Mauro Villanueva-Monzón
floater, developed with Germany’s University of Stuttgart, is based around a square, open-centred concrete platform, moored to the seabed using a catenary-style spread of chain lines, or hybrids of chain and synthetic rope, with “soil-specific” anchors.

The design, which derives stability and buoyancy in large part from an arrangement of airtight internal chambers around a square “damping pool”, is foreseen for mega-class turbines of up to 10MW floating in water depths of 40 metres or more.

The Navantia/Olav Olsen unit is likely to be a steel semi-sub based on a triangular design inspired by the North Sea oil and gas industry’s experience in building deep-water platforms, although a spar-type concept is also on the table.

The triangular pontoon derives much of its steadiness at sea from being moored partly submerged, with further stabilisation provided by damper plates at the base of each of its three columns and a tower brace system supporting the turbine.

“The 2MW and 3MW are turbines that we [Gamesa] and Acciona already have in our portfolios; they are proven machines, well-known by their manufacturers,” says Villanueva-Monzón. “We will make the modifications we know are needed for these machines to operate in the deep offshore.”

Because of their confidence in the turbines — as well as time and funding pressures — the two companies have leapfrogged scale-model testing to “go direct for full-scale 2MW and 3MW machines”, with a view to eventually scaling up both designs for 5MW-plus floating models.

“It is a trade-off between reasonable risk and cost. We feel the turbine and floating foundation in combination will work well and give us the opportunity to explore how the technology will make the next jump in size.

“Knowing the 2MW and 3MW turbines as we do, there will be less uncertainty: during offshore testing we will be able to get to the root cause of any problems more quickly, and the size of these machines will still allow us to extrapolate conclusions for the next generation of wind turbine designs of the 5MW class and larger.”

Gamesa and Acciona have already cut their teeth on similar “mid-scale” floating concepts through testing programmes run as part of the Flottek and HiPRWind joint industry projects.

With construction scheduled for next year, installation of the FloatGen prototypes could happen in the first half of 2015, with 2016 dedicated to monitoring and testing the units in the open seas, overseen by German research organisation Fraunhofer IWES and environmental consultancy RSK.

Although siting plans will not be cemented for several months, Villanueva-Monzón says deployment will be at one of several Spanish ocean-energy research stations, such as Zefir, planned in the Mediterranean; Bimep, in the Bay of Biscay; and Plocan, within sight of Gran Canaria, off northwest Africa.

“Choosing a site is central to the business case of each prototype,” he explains. “We have to contemplate the seabed soil type for anchor points, the wind resource, the wave environment — the Mediterranean and the Atlantic are very different, for example — and the logistics of the fabrication, transportation and installation.”

Although the two floaters are being progressed “hand in hand”, their one-of-a-kind designs mean they may end up being put through their paces at separate locations.

“The technologies ultimately are better suited to some sites than others. And then there is the supply chain and the construction process that feeds into the business case for each, which varies by region,” Villanueva-Monzón points out.

“What we are developing is approaching offshore wind in a way that is very different from onshore wind. In terms of the technology, the logistics, the manufacturing processes, it is like offshore is sumo wrestling and onshore is Greco-Roman.

“By the end of 2016, we will know if these floating concepts are viable and what their true costs are in operation and what cost of energy they can produce.”