Bottom-fixed offshore wind

Mature technology, but challenges for increased performance

Bottom-fixed offshore wind technologyis emerging in Northern Europe as one of the main sources of renewable energy. At sea, as winds are more stable and often of higher average speed, offshore wind farms have a load factor of 45%, i.e. twice as high as a French onshore wind farm (22%) and 3 to 4 times higher than photovoltaic installations in France (15% maximum in the Southern Region). Since 2010, global offshore wind capacity has been growing at around 30% per year. The technology is now mature and the average cost of the energy produced has become very competitive. Challenges remain, however, to further improve the performance of bottom-fixed offshore wind sector and to integrate it into the energy mix of a number of countries, particularly France, which has the second largest coastline in Europe.

Bottom-fixed offshore wind sector faces technological, logistical and socio-economic challenges

The main challenges for a deployment of bottom-fixed offshore wind sectorposed in France and in countries with geographical or political similarities are :

• The integration of commercial wind farms into the maritime activities already in place on the French coasts, with first and foremost transport and fishing already fully integrated into zoning decisions;
• The setting up of an industrial sector and dedicated port areas to manage the construction of a farm. As an illustration, the rotor disc of a 15 MW wind turbine is more than 200 m long and a farm has 35 to 50 machines;
• The construction of an installation and maintenance chain with adapted means: boats for transporting large-diameter blades, masting systems at sea, intervention on nacelle, storage place for repairs in the port…;
• The new generations of turbines whose increasing unit power implies the use of rigid piles for which standard design methods are not adapted;
• The poorly known carbonated soils present on the seafront of Northern France;
• The economic attractiveness that requires achieving an average cost of energy produced that is competitive with other sources of decarbonated energy. This concerns the optimum between the full costs of a wind farm and production, but also access to financing;
• Socio-economic policies that set the framework for the medium- and long-term deployment of energy production technologies;
• Applicable regulations and the acceptability of projects can lead to significant delays that then limit the deployment of technologies.

In France, the first calls for tenders for commercial bottom-fixed offshore wind farms were launched in 2011. However, it was not until 2019 that the first one was fully authorised and orders were placed for work to start in the wake. In 2019, the proposed tariff for the new wind farm awarded by the French government also reached very competitive levels.

Characterising winds and seabed, studying environmental pressures and induced effects

All the activities of France Energies Marines contribute to providing solutions to the bottom-fixed offshore wind sector. This is mainly achieved through collaborative R&D projects which allow in particular to :

• Reduce uncertainties on the characterisation of wind resources and thus contribute to the optimization of production (CARAVELE project);
• Better characterise the physical environment such as wave fields, but also soils, and thus integrate more precise data for the design of systems (DIME and GEOSISMEM projects);
• Better characterise sediment transport, particularly that linked to the movement of underwater dunes, while integrating the study of the ecosystem (DUNES project);
• Better evaluate the interactions with soils representative of French sea facades (including carbonated soils) taking into account the new rigid behaviour of monopiles in order to design the foundations for a 30-year life span (SOLCYP+ project);
• Optimise environmental, societal and economic impact studies by proposing original models integrating the ecosystem in the broadest sense to support project acceptability (TROPHIK, APPEAL and WINDSERV projects);
• Evaluate the environmental impacts of certain components or systems used in ORE farms, such as galvanic anodes (ANODE project) or power export cables (SPECIES project), and thus help change the regulatory framework;
• Propose environmental monitoring solutions such as passive acoustic monitoring of benthos (BENTHOSCOPE and BENTHOSCOPE2 projects) and characterisation of biofouling on submerged components (ABIOP and ABIOP+ projects).

These various studies provide the sector with validated models, adapted measurement methods, representative data and recommendation reports based on recognised expertise. The COME3T approach contributes, for example, to the acceptability of projects by offering summary reports for a very wide audience. These cover a wide range of topics related to the environmental integration of ORE, for which the scientific experts in the field provide neutral and independent insight.

Photo credit: Fokke / AdobeStock

Interlocutors

Guillaume Damblans

Design and Monitoring of Systems R&D Manager

Herveline Gaborieau

Head of Development and Valorisation

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