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Offshore Wind Farm

R&D mobilised to meet the challenges of floating offshore wind energy

By EDF | Posted June 28, 2021

Connections, maintenance and environmental impact are all key issues to which R&D is fully committed. Marie Berthelot, Head of R&D Renewables and Offshore Wind R&D project leader at the R&D UK Centre, focuses on the area of maintenance.  All these multi-disciplinary teams have very diverse but complementary areas of expertise to successfully achieve Net Zero.

Maintenance: an extraordinary challenge

Maintaining and repairing moving infrastructures on the high seas is an extraordinary technical and logistical challenge. The aim is to ensure the safety of operators and reduce maintenance costs. Here's a look at the R&D challenges involved in maintaining floating wind farms.

How to replace monumental components more than a hundred kilometres from the coast? How to ensure the safety of technicians during offshore operations? How to remotely monitor the infrastructure? These are just some of the questions that fuel the work of R&D.

The subject of floating wind farm maintenance is complex, especially since EDF does not currently have any floating wind turbines in service. On the other hand, EDF has advanced expertise in fixed offshore wind farms, notably with the operation of the Teesside and Blyth wind farms in England. In theory, the maintenance of floating wind turbines is like that of fixed wind turbines. "It consists of light maintenance through regular monitoring, inspection and maintenance of all the elements of the wind turbine and heavy maintenance when it comes to intervening on large components such as the mast, blades, generator and electrical connection cables," explains Marie Berthelot. In practice, these heavy operations are made more delicate in the open sea, given the moving nature of floating wind turbines, the depth of the water and their distance from the coast.

Safety: a priority

The first challenge is logistical management and team safety. The weather windows and the distance to be covered to reach the wind turbines make it difficult for the vessels to get to the site. "What can be planned on a daily basis for most fixed offshore wind farms will require more anticipation and longer times for floating wind farms, and therefore higher costs," says Marie Berthelot. To that end, we are developing a tool to define the logistical scenario that maximises the availability of the farm and reduces maintenance costs throughout the farm's life.

Operator safety is also a key issue that R&D is focusing on. "In a few decades, floating wind turbines will be able to generate 15 to 20 MW of power, which means nacelles weighing close to 700 tons, fixed at a height of over 100 metres. "Transferring teams from a boat to a float in complete safety is one of the subjects that R&D is working on. "We are currently testing an innovative monitoring system on board the vessel to help the pilot make decisions during crew transfers. " This means trained personnel and adapted maintenance platforms.

Focusing on innovative maintenance vessels

Part of the challenge is to adapt heavy maintenance vessels.

Today, vessels are designed for the specificities of fixed installations - jack-up vessels anchor in shallow sea beds to allow the use of cranes to lift and lower heavy loads. Tomorrow, floating farms will be in depths of up to a few hundred metres. "We won't be able to use the same type of vessels... which we need to incorporate into our studies now. R&D is taking a closer look at innovations in this sector to adapt the maintenance strategy for future floating farms.

Two maintenance scenarios

What strategy should we adopt? "Two scenarios are emerging," says Marie Berthelot. Floating wind farms have an advantage: they can be disconnected from the electrical system and towed to port. Less waves and wind and more peaceful working conditions...although this option may be attractive, it is not unanimously accepted. "In addition to the technical complexity and the cost of disconnection and reconnection to the network, and the time required to repatriate the wind turbine, it is also necessary to anticipate the size of the port infrastructure to accommodate them.

While opinions are not yet clear-cut, engineers are leaning towards offshore maintenance. However, it remains conditional on the adaptation of vessels.... But also to the evolution of monitoring and surveillance systems. Obtaining information remotely via autonomous systems is one of the key R&D challenges. "Sensors deployed on all the components of the wind turbine to measure its health and analysis of the operating data of the various elements are all essential information to enable us to set up advanced diagnostic methods. We are also interested in the use of drones capable of going on-site to inspect underwater components, such as the cables and the float, but also aerial components, such as the tower and the blades, and even to carry out light maintenance operations, such as cleaning surfaces colonised by marine growth. A first experiment in cleaning by drone will be carried out in the basin this year to test its effectiveness.

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