Offshore wind energy will make a key contribution to achieving the EU’s Green Pact targets. The European Commission’s Offshore Renewable Energy Sources strategy anticipates the integration of 300 GW of offshore wind generation capacity into the power system by 2050. The magnitude of this transition will pose new challenges for the European electricity system: achieving the necessary connections and grid development at the lowest cost; maintaining system security; accommodating a complete redefinition of energy flow patterns; considering key constraints related to spatial planning, environmental protection and public acceptance; achieving an integrated perspective across time, space and sectors; and ensuring flexible resources to keep the energy system balanced.

To date, there are 227MW of fully operational floating wind across 14 projects in 7 countries. Globally, there are 46MW under construction, 576MW approved for construction, 68GW are integrated into planning or have a siting agreement (80 projects) and 175GW are in early stage development or in the process of obtaining offshore permits (177 projects).

ACCIONA Energía is in a strategic position, given its extensive experience in the development and operation of renewable assets, boasting a portfolio of 11.8 GW and a geographical presence in more than 15 countries across all five continents. ACCIONA Energía is committed to participating in this new technological challenge and is taking concrete steps to position itself as a competitor in the growing Offshore Wind market.

In this context, the company is evaluating offshore wind technology in diverse locations such as the Atlantic and the Mediterranean. In these areas, the absence of a continental shelf and consequently, the high depths, prevents the installation of fixed structures on the seabed. Therefore, it is necessary to develop floating wind technology in these locations.

In the case of offshore wind farms, both floating and fixed structure, compliance with grid codes is a complex task to address. This is because changes in the available power due to variations in the wind resource can lead to issues with the quality of energy, exacerbated by evacuation infrastructures that increasingly have a greater impact given their scale and the long distances traveled from the energy source (turbines) to the point of connection to the transmission grid.

One of the major technical challenges of Floating Offshore Wind (FOW) technology is the design and evaluation of the electrical interconnection scheme, owing to various factors:

• Long distances from turbine installations to the coast, with the additional distance from the coast to the Interconnection Substation.
• Technological barrier to having Floating Transformer or Conversion Substations, which allow for the elevation of the electrical supply voltage from the plant or the use of High Voltage Direct Current (HVDC) technology in deep-sea locations. This limits evacuation options to High Voltage Alternating Current (HVAC) technology.
• Highly capacitive nature of submarine and terrestrial cables (environmental limitations for using overhead lines in the terrestrial evacuation section compel the majority of projects to use buried cables). This implies the need to absorb large amounts of reactive power both at the turbine and through reactive compensation elements, which, due to physical limitations, are located in the onshore substations.
• Limitation of the maximum allowable voltage in submarine HVAC cables, with dynamic capacity (in the sense that they have flexibility and the ability to undergo mechanical stress, due to the floating nature of the turbines). Currently, the standard voltage in Dynamic Inter-Array Cables is 66kV, although 132kV technology is expected to become commercially available in the medium term.

With these premises, we are faced with the design of the electrical evacuation system and the sizing/location of the reactive power compensation elements. Even in the conceptual design phase, decisions on the above-mentioned points will have a significant impact on the cost, performance and viability of the projects under development.

ACCIONA Energía is launching this challenge to identify and expedite the development of tools and/or technologies that enable the evaluation of designs and optimization of power evacuation systems for offshore wind farms. The proposed design and optimization methodologies will consider integration with the grid and compliance with the grid code of the evaluated projects, aiming for the automation of iterative design processes. The proposed electrical schemes should strike a balance between technical feasibility and the lowest possible cost.

The proposed solutions should:

• Allow for the modeling and simulation of the plant under study in electrical network analysis software that solves load flows (e.g., PSSE/DIGSILENT PowerFactory).
• Analyze sensitivities in the design and its feasibility, understood as compliance with grid code requirements at the project’s connection point and/or machine terminals, as well as voltage profiles along the evacuation scheme:
  • Compensation strategies: location, sizing, technology, and/or;
  • Evacuation schemes: number of circuits, voltage level, distances.
• Enable the evaluation of electrical losses, as well as the reliability of the system (redundancy/oversizing criteria).
• Be adaptable and scalable for deployment in various target markets and/or key design premises, such as HVAC/HVDC technology, HVAC with a marine substation, or direct connection to the ground.

Tools with different degrees of technological maturity will be considered, and it is not necessary for the proposed solution to be fully developed at the time of submission.