Techno-economic comparison and optimisation of grid planning scenarios for AC/DC grids: a North Sea case study

AC/DC grid reinforcement options. It is applied to a prospective multi-purpose Multi Terminal

Direct Current (MTDC) grid in the North Sea considering the modelling of the Continental

European grid and the Great Britain grid. The study is carried out within the HVDC-WISE project (https://hvdc-wise.eu/).

The study begins by modelling the 2020 European transmission system with focus on the areas of interest near the prospective MTDC grid. Two contrasting 2040 macro-scenarios are then developed – one with conservative and one with ambitious renewables development – reflecting different projections of generation, storage, and demand growth. For each 2040 scenario, three

North-Sea reinforcement philosophies are examined: (i) point-to-point HVDC links; (ii) hybrid interconnectors (radial MTDC grids) combining offshore wind connections with interconnection capacity, and (iii) meshed MTDC grids.

The proposed methodology is based on a techno-economic analysis that couples annualised capital expenditure (CAPEX) with the expected reduction in operating expenditure (OPEX) for the European system. Annual OPEX is derived from full-year (8760 h) multi-period optimalpower-flow simulation that minimises system-wide operational costs, including generation and 1 load shedding. The combination of three features makes this approach innovative. First, the

AC/DC model contains a detailed bipolar MTDC representation with a metallic neutral return, allowing realistic unbalanced operation after pole loss. Second, grid reliability is captured through multiple year-long micro-scenarios that introduce AC and DC equipment outages as well as varying supply–demand conditions; expected annual cost is obtained by averaging the

Optimal Power Flow (OPF) results across these scenarios. Third, system flexibility is explicitly considered by solving multi-period OPFs so that storage dispatch respects state-of-charge constraints. The annualised CAPEX and expected OPEX are then merged into two keyperformance indicators that express the net yearly benefit and benefit cost ratio of each reinforcement option.

This framework enables a comprehensive comparison of the three reinforcement strategies, including sensitivity analyses to assess the robustness of findings. To perform the methodology, all simulations in this article are carried out with the open-source tool HVDC-WISE TEA

(https://github.com/HVDC-WISE/HVDCWISE_TEA.jl) which natively supports the features above.