Offshore transmission network and Multi-Purpose Interconnectors: Optimal Configurations for the System

Looking ahead, as floating technologies achieve greater maturity, the potential role of MultiPurpose Interconnectors (MPIs) in the Mediterranean region could be leveraged in a fully decarbonised future energy system. Such interconnectors could enable combined solutions that collect offshore wind generation, link different market zones, and provide additional system services, including energy storage and green hydrogen production.

Recent analyses carried out by the Italian Transmission System Operator, Terna, have explored the prospects of implementing MPIs within Italy’s electricity system.

This article examines an additional topic of significant relevance: the impact that various offshore meshed grid configurations, when connected to the onshore network, may have on overall system costs, considering the incentive schemes established by policymakers.

Moreover, changes in Socio-Economic Welfare (SEW) benefits and the mitigation of system overgeneration have been analysed using hourly market simulations conducted under a longterm scenario for a selected test area of the Italian power system.

Considering current energy policies and offshore wind generation targets, the new Offshore

Network Development Plan (ONDP), published in January 2024 and incorporated into ENTSOE’s Ten-Year Network Development Plan (TYNDP), presents the first comprehensive longterm vision for offshore energy sector development and serves as a strategic planning instrument at the EU level.

The rollout of Offshore Wind Farms (OWFs) and hybrid infrastructures such as MPIs demands thorough evaluations of market designs capable of ensuring optimal resource utilisation while guaranteeing fair compensation for market participants. To support this transition, multiple discussions are underway at the EU level, addressing key issues such as:

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• market frameworks for MPIs; support mechanisms for OWFs within hybrid configurations. In this paper, zonal market simulations by the means of the official Day-Ahead Market (DAM) simulator employed in cost-benefit analyses within the National Development Plan have been performed to evaluate the performance of various MPI configurations, each featuring an increasing degree of structural complexity. These simulations were carried out under a longterm energy scenario characterised by a high share of renewable energy capacity, considering a test system.

For each configuration analysed, the effects on key system performance metrics were assessed, specifically focusing on Socio-Economic Welfare (SEW) and overgeneration – referring to renewable energy generated but not integrated into the system. Moreover, to ensure a comprehensive evaluation of the economic efficiency of these configurations, the total system cost was calculated for each scenario.

The results obtained outline that MPIs represent a highly promising solution for the efficient integration of offshore resources. In particular, meshed configurations consistently demonstrated superior performance compared to single MPI setups, delivering advantages from both economic and operational perspectives. Additionally, incorporating integrated multisector elements such as energy storage and electrolysers further improved overall system performance.

These findings underscore the significant potential of hybrid offshore designs in advancing decarbonisation objectives.