Floating farms turn the tide: deepwater offshore wind farms7 July 2015
With Hywind’s evaluation phase complete and other projects in progress across the globe, it would appear we are becoming more receptive to the idea of deepwater offshore wind farms. But despite tangible progress, we shouldn’t expect commercialisation for a while yet, as Trine Ingebjorg Ulla, head of business development floating wind at Statoil, tells Ross Davies.
It has been more than five years since Statoil, the Norwegian state-owned oil company, installed Hywind - the world's first operational deepwater floating wind turbine - off the island of Karmøy.
How time flies. When the Siemens-constructed Hywind 2.3MW prototype was first towed out to the North Sea in early June 2009, and subsequently planted on a floating tower with a 100m-deep draught, the concept of the floating turbine was still fanciful.
Fast forward to the present day, and optimism around offshore wind and its ability to meet our mounting energy needs is higher than it has ever been. According to the European Wind Energy Association (EWEA), about 150GW of offshore wind could be deployed on the continent, meeting 14% of the EU's total electricity consumption.
Over the past few years, a number of other floating wind farms have passed proof-of-concept and are now being prototyped, as players target commercialisation.
In 2011, US company Principle Power installed the WindFloat, a semi-submersible three-legged triangular pontoon, off the coast of Agucadoura. The 2MW-turbine structure has been generating power since 2012.
Further afield, Japan has arguably become the world's greatest exponent of harnessing floating offshore wind power. Since the 2011 earthquake and ensuing explosion at Fukushima Daiichi nuclear power plant, the government has sought to rely less on the atom, and use safer and cleaner energy alternatives.
In November 2013, Japan's first floating turbine was launched off the coast of Fukushima. Sniffing market potential, home-grown industrial giants Mitsubishi and Mitsui are in a race to install the world's largest wind farm - able to produce 1GW - by 2020.
"We recently submitted our environmental statement [for the 30MW pilot park off the Aberdeenshire coast] in the hope of being granted a contract later this year."
The potential benefits of offshore wind are not lost stateside either. Following up on the US Department of Energy's pledge to look into the viability of installing turbines on both seaboards, Principle Power this year announced plans to build five floating foundations to support 6MW turbines off the coast of Oregon.
"There has definitely been a shift in perception as to the advantages of offshore floating wind farms since the first Hywind Demo was deployed," says Trine Ingebjorg Ulla, head of business development floating wind at Statoil. "You only need to look at all the recent developments in the market.
"Testament to this is that many of these initiatives are also supported by national governments, as well as the EU. I think people now realise it is possible to have floating turbines - the technology is proven."
With the exception of parts of the Baltic Sea and the southern area of the North Sea, almost all of the world's oceans are deeper than 45m. This renders the manufacture of bottom-mounted turbines for such waters an almost pointless - not to mention costly - undertaking.
Hence the rise of floating designs in deeper waters, which can currently be compartmentalised into three categories. Companies such as Principle Power, Mitsubishi and Mitsui have favoured semi-submersible platforms, which give stability by mainly lying below the sea's surface and using water as ballast.
Hywind, on the other hand, makes use of the spar design - an elongated single column loosely moored to the sea floor, which extends far below the water so as to check movement, and uses sand and water as ballast.
The third category, the tension-leg platform - also deployed by Mitsui - is fettered to the seabed by tautened cables. However, it has proven to be unsuitable for stretches of water that are prone to higher tidal ranges.
Demo passes the test
Having generated energy off the Norwegian coast since 2010, the 2.3MW Hywind Demo is widely considered to have passed its evaluation stages with flying colours, with results exceeding expectations. The next step will constitute a 30MW pilot park (generated by five 6MW turbines) situated 25-30km off the Scottish coast of Aberdeenshire. It is hoped that the project - currently awaiting final permits from the Scottish Government - will further demonstrate the cost and risk benefits of floating wind farms in deeper waters (in this case, exceeding 100m), in contrast with fixed-bottom alternatives.
"We have come a long way in planning this project," says Ulla. "Talks began with the Scottish Government back in 2013, and we recently submitted our environmental statement in the hope of being granted a contract later this year.
"The plan is for the park to be connected to the local grid in Peterhead via an export cable. There will be no offshore substation. We are confident we will be able to verify not only the design, but also cost reductions in a commercial setting."
Benefits and barriers
In terms of manufacturing, floating wind turbines carry a number of advantages. As Ulla explains, structures naturally lend themselves to standardisation, mass production and a potential reduction in fabrication costs. Yet, there are still several logistical hurdles that need to be addressed if commercialisation is to take place. First, there are marine and meteorological factors to consider: with deeper waters come fiercer winds, and stronger waves and currents. How, for instance, has Hywind been able to withstand purported waves of up to 19m and 90mph gusts in the North Sea over the past five years?
"We have been able to keep the platform stable through a mix of design and stabilisation measures," answers Ulla. "For example, our design has a very narrow water line, about 8-10m, which reduces the effect of the waves. In addition, the structure is heavily ballasted, which lowers its centre of gravity and counteracts heave motions.
"Then there's also the benefits of a flexible mooring system, which allows the turbine to avoid piling. It's actually no different to what's deployed in the oil and gas industry, with which we [Statoil] have plenty of experience. It's just a different application."
To deal with inordinately powerful winds, which risk setting the turbine off in a pendulum movement, Hywind also makes use of a patented motion-control system. Connected to the turbine's pitch-control system, it automatically moves the structure back in a pitch movement, releasing some of the force of the wind in the process.
"It's a system that functions very well; it deals with some of the pressure by rapidly pitching the blades," says Ulla. "The capability to maintain control over these elements and keep the turbine stable is very important. In so doing, you will increase production and also reduce stress on the construction."
As Ulla suggests, players are seeking to cut their expenditure at any available opportunity. One way of achieving this is to assemble turbines in sheltered waters and, in turn, drive down the higher costs associated with offshore operations and eliminate potential weather risks. "Being able to do assembly onshore is a big advantage," says Ulla.
A more considerable long-term challenge, she says, will be tightening up the supply chain of floating offshore wind structures.
"The industry still lacks a supply chain, which means it might be a few more years before we can compete," explains Ulla. "And the trouble with prototypes is that the costs are always sky high. So we need a supply chain to come around and really make this a competitive technology. I believe that will start happening once the business opportunity is there."
According to the EWEA, it is feasible that a full-scale offshore wind farm could be in operation by 2017, although it has warned that "a supportive legislative framework is needed" for the goal to be realised. Going by rate of progress, it is more likely that we will see a commercial offshore wind utility realised in Japan first. As Ulla says: "In a market such as Japan, floating wind is just about the only energy option it has [aside from the gas imports on which it is currently reliant]."
Undoubtedly, deepwater floating offshore wind has gained enough traction in recent years to make it a genuinely exciting renewable energy sector. Clean and with the potential of standardisation, we should expect to see greater levels of investment moving forward.
Nonetheless, commercialisation could take time. Despite Statoil's reputation as a pioneer in the field - its investigations into offshore wind foundations date back to the turn of the century - the group has come out on record as saying it does not expect to deliver any utility-scale wind foundations until 2020 at the earliest.
Ulla appreciates this, but it does not stop her being enthusiastic about the future. "It might take a few more years, but we will get there in the end," she says.
Trine Ingebjorg Ulla
With more than 20 years' experience in energy, Trine Ingebjorg Ulla is head of business development floating wind at Statoil. She is chairman of Hywind's board of directors and has held other management positions in marketing, market analysis and development planning.