An international consortium says offshore windfarms built across the North Sea in ‘hub and spoke’ fashion are feasible and could help countries in the region achieve climate goals
The consortium, the North Sea Wind Power Hub, has published the results of an assessment phase of a study analysing the feasibility of one or several wind power hubs in the North Sea. It aims to facilitate the large scale roll-out and integration of offshore wind in the North Sea at least cost to society while maintaining security of supply, as part of the transition to a low-carbon energy system.
Its vision is based on an internationally co-ordinated roll-out of hub and spoke projects, combining windfarms in the North Sea with interconnectors to the onshore energy grid. The concept also includes the potential for power-to-gas, such as producing green hydrogen.
The consortium found that the proposed hub and spoke concept is technically feasible and that a gradual roll-out of 10 to 15-GW hubs “is the next logical step” towards large-scale build-out of offshore wind energy.
An initial hub and spoke project would probably be connected electrically to shore but adding power-to-gas and the production of green hydrogen could provide greater energy system flexibility from the 2030s onwards.
“While it is possible to build a first hub and spoke project within the current regulatory framework, under existing EU and national legislation, significant changes would be required at national level in terms of planning and policy to allow for integrated infrastructure projects such as the modular hub concept,” the consortium said.
It believes that were a hub and spoke concept based on 10-15-GW hubs implemented in the North Sea up to 180 GW of offshore wind capacity could be built by 2045.
“An internationally co-ordinated approach could connect and integrate large-scale offshore wind more effectively and with significantly lower costs compared to purely national projects,” the consortium said.
By combining offshore wind transmission and interconnection infrastructure, windfarm hubs could leverage synergies to increase asset utilisation, reducing the cost of both functions. They could also reduce the need for grid extensions beyond 2030 by internationally co-ordinating onshore connection of offshore wind energy, and by using power-to-gas conversion and adapting and utilising existing gas infrastructure.
The consortium examined hubs of varying sizes and concluded that smaller hubs reduced the benefits of scale that 10-15-GW hubs provide. Increasing hub size also has limitations: turbines would be connected to a hub through inter-array cables and if larger windfarms are connected, the inter-array cables become too long and AC collector platforms are required to connect wind turbines. These collector platforms would increase costs.
Hub substructures could use different types of foundations, including sand islands; caisson islands, which are suitable for smaller hubs of approximately 6 GW and in water depths of less than 25 m; and platforms, using a jacket or gravity-based structure as foundation.
The partners in the project also examined different types of hubs, including an all-hydrogen concept that would convert all of the wind power produced offshore to hydrogen and transport it through pipelines to shore.
Two types of electrolysis units were examined: alkaline and proton exchange membrane. Hydrogen produced by them would be compressed to a pressure of 50-70 bar for transmission to onshore connection points and storage locations.
“Depending on the scope of development, hubs could provide the foundation to supply hundreds of millions of Europeans with green energy,” the consortium concluded.