The primary objective is to evacuate offshore generated energy to shore as efficiently as possible. We have considered four concepts: Business as Usual; National Distributed; European Centralised, and European Distributed. All case studies assume HVDC connectivity required over longer distances, but with different types or levels of meshing. These concepts represent possible routes for the development of offshore grid infrastructure. They illustrate different levels of cooperation between countries and different levels of integration and meshing. Each concept is further worked elaborated to evaluate the performance of more detailed architectures required to operate such a grid, and hence the costs and benefits associated with each concept.

Business as Usual (BAU) is our reference scenario – and in fact may be overtaken by reality. We are assuming that the offshore grid will be developed to evacuate all offshore wind to the national grid within the North Sea country's Exclusive Economic Zones (EEZ); Offshore wind farms will be connected to shore individually or through small national hubs; Separate interconnectors are added for market integration purposes; Nationally designed market arrangements will predominate (the EEZ remains an extension of the national bidding zones / support schemes remain nationally organised); There are limited cross-border power flows through the offshore grid. Wind farms are radially connected (point-to-point), in groups no larger than the AC power infeed (based on onshore grid codes, e.g. 3 GW for mainland Europe); Separate point-to-point interconnectors facilitate interconnection between countries (either on- or offshore); Offshore wind farms are connected to a single country (within its own EEZ); DC grid protection is based on decoupling onshore at the AC side.

National distributed hubs: This assumes the grid is developed to evacuate all offshore wind within an EEZ to the respective national grid; Offshore wind farms are connected to shore individually or through small (national) hubs; Interconnection may occur through offshore grid connections at times of relatively low wind production; Nationally designed market arrangements and support schemes are as in the BAU; Cross-border power flows are possible, but may be tempered by national motives, and are considered a secondary goal. In this case wind farms can be connected to two countries, but this is anticipated to be infrequent; HVDC connections (multi-terminal) shore-OWF-shore; Hybrid assets exist: interconnection between countries using wind farm connection (at times of relatively low wind production); Grid protection based on AC and/or DC decoupling. High voltage DC circuit breakers will be required when flow size is above the AC infeed limit.

European Centralised hubs: This considers the scenario where there is joint development of an offshore grid able to evacuate all offshore wind generation to the combined onshore grids of bordering countries; Offshore wind farms are connected radially to large-scale hubs, the hubs connected to shore / other large hubs; Connection capacity to individual countries is potentially oversized with respect to production within own EEZ (although total sending capacity need not exceed total generation capacity, some interconnection capacity may be built in); International cooperation is anticipated in market arrangements and support schemes; large cross-border power flows take place. Radially connected wind farms are connected to large central hubs (islands - the illustration shows only one, but more will be required to cover the coastal area); Central hub architecture is either multi-terminal HVDC or an AC super node; In the latter case, point-to-point HVDC connections are laid from hub to shore (various countries); There may be potential meshing on the DC side between hubs; Grid protection based on AC and/or DC decoupling.

The European Distributed model assumes joint development of a meshed offshore grid able to evacuate all offshore wind to the combined onshore grids of bordering countries (generation in a single EEZ may exceed the ability of its respective grid to accept all generated wind energy); Offshore wind farms are connected to smaller hubs, these hubs are connected to shore and "meshed" to provide alternative paths; Connection capacity may potentially be oversized with respect to production within own EEZ (although total sending capacity need not exceed total generation capacity, some interconnection capacity may be built in); International cooperation is required on market arrangements and support schemes;  Greater capacity to provide cross-border power flows is planned for. HVDC meshed grid is designed consisting of multiple interconnected hubs; Interconnection is available through meshing of hubs; There are multiple HVDC (multi-terminal) connections; The topology allows for alternative pathing (redundancy); The widespread meshing requires DC grid protection.

Each of these concepts is applied to the same wind generation scenarios, i.e. the eventual generation occurs in the same place; only differences in strategy will be compared. Following the specifications of these concepts, we are now developing more defined topologies for the anticipated roll-out of wind generation in the North Sea. The Work Package team is now translating this into a series of alternative technical solutions which we then evaluate both on cost and performance as well as social benefits.