In October, the French developer Quadran announced a partnership with foundation maker Ideol to co-develop up to 500MW of offshore power by 2020, using a floating square concrete platform design that can provide ample surface area for O&M at the...

By Jason Deign

It is barely a couple of years since France got serious about offshore wind. But already the country is looking far over the horizon, with plans for a number of deepwater, floating turbine designs in the offing.

What is more, at least one design promises to make life easier in terms of operations and maintenance (O&M).

In October, the French developer Quadran announced a partnership with foundation maker Ideol to co-develop up to 500MW of offshore power by 2020, using a floating square concrete platform design that can provide ample surface area for O&M at the base of the turbines.

The design, which is intended for turbines of up to 10MW and includes a damping pool to minimise dynamic stresses, would allow for a significant amount of O&M to be carried out without having to bring a vessel alongside the turbine.

There is even the possibility of winching entire blades up into place from the turbine base, doing away with the need for a crane vessel. If engineering crews need to get to a turbine quickly, the base can double up as a helicopter landing pad.

Paul de la Guérivière, chief executive at Ideol, has previously told Wind Energy Update that this design could overcome a significant O&M challenge for floating turbines, which is how to deal aboard a moving foundation from a moving vessel or helicopter.

According to Ideol the foundation has been designed with a minimal life time of 25 years. The structure of the hull and tower is based on the 50-year return period design event, the mooring system with the 100-year return period and some components like the umbilical and mooring subsea connections with a 200-year return period.

Based on concrete fabrication and without any active ballasting/pumping systems, the maintenance requirements and costs are minimized with a class renewal every 5-year only with hull underwater and mooring lines inspection, claims the company.

Easier O&M

“We have proved it will be the same or easier,” he said.

Quadran and Ideol are planning to put the design to the test in 2015, when they will fit it to a 2MW Gamesa turbine off the coast of Gran Canaria, Canary Islands. Gamesa is currently using Arinaga Quay in Gran Canaria as the test site for its G128 5MW offshore product.

Aris Karcanias, managing director of economic and financial consulting at FTI Consulting, called the Ideol design “a step in the right direction.”

He says: “You would need to run the numbers but the claims that they are making do stack up. If it doesn’t need a crane, that’s a huge benefit. So far, for floating technologies developers have been more focused on whether we can operate in deep waters.

“There hasn’t been much thought about how we can integrate this with a life-cycle solution. This is promising design from Ideol; I think it’s the right move.”

Ideol is not the only floating product being designed for the French market, however.

Winflo design

A consortium led by the defence-to-energy conglomerate DCNS is aiming to commercialise a design called Winflo in which the foundation resembles an upside-down, three-legged stool, with the tips of the legs floating above the water.

The Winflo design project is also backed by the renewable energy developer Nass&Wind, the French wind turbine manufacturer Vergnet, the French Research Institute for Exploitation of the Sea (Ifremer) and the ENSTA Bretagne engineering graduate school.

DCNS says the design should allow for the installation of turbines as depths greater than 50 metres and is aiming to develop its first commercial offshore wind farm, with up to 100 machines, by 2020.

According to DCNS’s web site, Winflo generators will be equipped “with an innovative semi-submersible flotation system, a lightweight generator designed specifically for this offshore application, and a special anchoring system.”

The consortium is aiming to test a demonstrator at sea in 2014. In addition, Wind Energy Update understands a third player is gunning for the French floating offshore market, although the proposal in question is said to be still “very early stage.”

Reducing costs

How these alternative designs measure up to Ideol’s in terms of O&M remains to be seen. In theory, floating turbines in general have the ability to reduce offshore O&M costs because there are no grouting or connection issues to deal with, as is the case with monopiles.

Furthermore, in case of a major failure a potential benefit of floating designs is that they can be towed back to port, although there is a question mark over how much economic sense this would make for machines moored very far offshore.

More importantly, though, Karcanias cautions that it is too early to say what floating turbine O&M will look like for sure because all the designs incorporate a number of unknowns. “You really are adding a lot of complexity with a floating system,” he says.

“From an engineering point of view, when you are looking at introducing additional dynamic loading on the structure, it could have an impact that we don’t know about today. That is something companies investing in these technologies are investigating.”

Detailed studies on the likely O&M costs of different floating designs are still hard to come by, he adds. But with the French now on course to get demonstration projects in the water within months, instead of years, it hopefully will not be long until some of these unknowns are resolved.

Floating off the USA

In May 2013, The US Energy Department recognized the nation’s first grid-connected offshore floating wind turbine prototype off the coast of Castine, Maine. Led by the University of Maine, the DOE proclaimed that the project represented the first concrete-composite floating platform wind turbine to be deployed in the world.

“Developing America’s vast renewable energy resources is an important part of the Energy Department’s all-of-the-above strategy to pave the way to a cleaner and more diverse domestic energy portfolio,” said Jose Zayas, director of the Energy Department’s Wind and Water Power Technologies Office. “The Castine offshore wind project represents a critical investment to ensure America leads in this fast-growing global industry, helping to bring tremendous untapped energy resources to market and create new jobs across the country.”

The government body said that the innovative floating offshore wind turbines, like the one launched in Maine, will open up new economic and energy opportunities for the country.

With the support of a $12m Energy Department investment over five years, University of Maine and its project partners conducted extensive design, engineering and testing of floating offshore wind turbines, followed by the construction and deployment of its 65-foot-tall Volturn US prototype. At 1:8th the scale of a commercial installation, the project is collecting data to validate and improve floating wind turbine designs, while helping to address technical barriers to greater offshore wind cost reductions.

The University of Maine design uses advanced materials that help reduce the overall cost of the system while ensuring high performance and efficiency. For example, the floating wind turbine features a unique semi-submersible platform that uses a lower cost concrete foundation in addition to a lighter weight composite tower.

As part of the five-year project, the Maine Maritime Academy helped test and conduct analysis on these pioneering designs, while Pittsfield, Maine-based Cianbro Corporation leveraged its experience in maritime energy infrastructure and ship building to construct this first-of-its-kind wind energy system.

More positive news

The Maine Public Utilities Commission in January 2014, in a 2-1 vote, approved terms for a project that would put two floating wind turbines off Monhegan Island as part of a test for the new technology. However, some permitting and other hurdles must be cleared before the turbines are built, according to a report by The Working Waterfront news site, published by The Island Institute.

According to news reports the PUC approval was needed because the Legislature, as part of its 2012 energy bill, requested proposals for developing offshore wind energy. Early last year, the Norwegian company Statoil was chosen by PUC, but under pressure by Gov. Paul LePage to reopen the bidding, Statoil withdrew from consideration.

Under the new request for proposals, the University of Maine, the Maine construction firm Cianbro and the Nova Scotia-based energy company Emera, operating under the name Maine Aqua Ventus (MAV), sought to win the test work, following their Castine project tests.

The principal designers for MAV, including Habib Dagher, the director of UMaine's composite centre, argue that new technology like the floating turbines needs public funding assistance until economies of scale are achieved and the cost of production drops. The US DOE could also be part of this financing equation as the underlying commercial prospects of US-dominance in this area of floating turbine technology could have a positive impact on the economy and the linked O&M service industry in the US and overseas.