By Jason Deign

Floating turbines are all the rage. Considered an exotic concept barely a year ago, the idea is now rapidly moving off the drawing board and towards commercialisation, with many large turbine manufacturers joining the fray. Vestas, for example, already has a prototype in the water. 

The WindFloat, a triangular floating foundation fitted with a Vestas V80-2.0MW turbine, is currently parked off the coast of Aguçadoura in Portugal, in a project carried out in partnership with the Portuguese utility Energias de Portugal Renováveis and Principle Power of Seattle, US. 

Next door in Spain, a consortium featuring Gamesa, Acciona, Alstom and Navantia is this year hoping to test a 1.5MW floating turbine at the Biscay Marine Energy Platform off the Basque Country. 

But perhaps the most noteworthy of the would-be floating turbine players is the group of industry heavyweights put together to float Japan’s renewable energy ambitions. 

Last March Marubeni Corporation and the University of Tokyo unveiled plans for an experimental offshore floating wind farm project comprising a 2MW turbine combined with the world’s first 66kV floating power substation. This is to be followed by two 7MW machines. 

Japanese heavyweights

Other partners in the endeavour include Mitsubishi Heavy Industries, IHI Marine United, Mitsui Engineering & Shipbuilding, Nippon Steel, Hitachi, Furukawa Electric, Shimizu Corporation and the Mizuho Information & Research Institute. 

Whichever way you look at it, it is clear floating turbines will soon be a reality in the offshore wind industry. What will this mean for operations and maintenance (O&M), though?

There is no simple answer to this question, not just because of the lack of real-life experience of floating designs to date, but also because of the bewildering array of flotation proposals currently under consideration. 

These range from Blue H’s submerged deepwater platform concept to Hexicon’s 500m, 24-turbine-carrying floating wind park idea. 

In any event, though, there are reasons to think the O&M challenges associated with floating turbines might not be as bad as the challenges associated with commercialising the designs in the first place. 

Connection issues

“You don’t have the grouting and connection issues that you have with monopiles,” points out Sjur Bratland, who project managed the launch of the world’s first floating turbine, the StatoilHydro HyWind, and is now managing director of INTSOK, a Norwegian oil and gas body.

With the HyWind spar or slender cylinder concept, he says: “You just have one pile, which could be cheaper and with less design risk in the long run. In oil and gas the spar buoy has been used for many years. You need a dynamic cable connection, but that is not a problem.”

One consideration, he adds, is that floating turbines would need to be surrounded by ample no-go zones for fishing vessels, so that nets do not get entangled in the anchor lines. But in many other respects Bratland believes O&M for floating turbines would be relatively straightforward. 

This is a view shared by Fabian Thalemann of the Fraunhofer Institute for Wind Energy and Energy System Technology in Kassel, Germany. “Floating is not the big difficulty, but where it is stationed,” he says. 

“The first point that comes to mind is of course that we are far offshore and not near shore. That means greater distances and shorter time windows for maintenance. Technician on-site times will be a critical issue, and flotel vessels will be a solution for that.”

More vessels

Turning to vessels generally, Thalemann believes the current designs will work without problems on the floating wind farms of the future. “The vessels wouldn’t change much,” he says, “except for the numbers. We need more vessels.”

Weather conditions can be harsher far offshore, of course, but by the same token waves and currents tend to be less of an issue, so in some respects O&M tasks might be easier. One final point, however, is how easy it will be to gain access to the turbines and their platforms.

Says Paul de la Guérivière, chief executive at the French floating foundation company IDEOL: “In terms of accessibility from a transfer vessel or helicopter, since the platform will be moving this could have an impact. But we have proved it will be the same or easier.”

The IDEOL foundation includes a damping pool system and is made of concrete so, says de la Guérivière, the only maintenance it needs is a five-yearly visual inspection of the mooring lines, which could be carried out by a remotely operated underwater vehicle. 

He adds that crews can even replace entire turbine blades without needing a crane vessel. Of course, alternative foundation designs might not be so user-friendly and, de la Guérivière concedes: “There will probably be a learning curve at the beginning.”

But at the moment, he feels, the good news is the upcoming transition to floating turbines “does not seem to be an issue in terms of O&M.”