To achieve climate neutrality, the Netherlands is phasing out fossil fuels and expanding renewable energy, with offshore wind playing a key role. The European Commission aims to increase offshore renewable energy capacity to 300 GW by 2050. As wind farms are built further offshore, high-voltage direct current (HVDC) technology is becoming essential for efficient grid connection. TenneT's 2GW program supports this transition by standardizing offshore platforms, enabling faster deployment and scaling of offshore wind energy to meet climate targets efficiently.

A critical component of these platforms is gas-insulated switchgear (GIS), which ensures safe and reliable operation by controlling the connection of wind turbines to the grid. Traditionally, GIS relies on sulfur hexafluoride (SF₆), a potent greenhouse gas with a global warming potential (GWP) of 24,300. In response to environmental concerns, Regulation (EU) 2024/573 mandates a phase-out of SF₆ in switchgear up to and including 145 kV by 2028, necessitating the transition to alternative technologies.

This study evaluates SF₆-free alternatives for high-voltage GIS in offshore converter stations, considering environmental impact, economic feasibility, long-term reliability, safety, technical performance, and regulatory compliance. A multi-criteria decision analysis (MCDA) is conducted, assessing 42 alternative gases and insulation technologies based on GWP, ozone depletion potential, flammability, toxicity, boiling point, and dielectric strength. Two viable alternatives emerge: a gas mixture of C₄F₇N, CO₂, and O₂ (GWP 301–614) and vacuum GIS insulated with clean air (GWP 0).

To determine the feasibility of both technologies for next-generation converter stations, expert interviews are conducted to identify key challenges and drivers. Challenges include its current voltage limit of 145 kV, larger space requirements, and limited supplier availability. A major driver is the transition from 66 kV to 132 kV inter-array cables, reducing the number of required switchgear installations from 40 to 24. This mitigates space constraints and makes vacuum GIS a viable long-term solution. Additionally, ongoing developments in vacuum switchgear technology reduce dependency on a single manufacturer.

A comparative life-cycle assessment (LCA) of SF₆, C₄F₇N, and vacuum GIS focuses on manufacturing and use phase emissions, as these contribute most to greenhouse gas emissions and exhibit the most significant differences among technologies. Results show that C₄F₇N technology has the lowest total emissions in these phases, as vacuum GIS production requires more aluminum, leading to higher manufacturing emissions. While sustainable aluminum sourcing could mitigate this, no regulatory or economic incentives currently exist.

This study concludes that vacuum GIS is the most viable alternative to SF₆ for offshore converter stations, aligning with future platform developments and regulatory compliance. TenneT is advised to prepare for a transition to vacuum GIS, supported by 132 kV inter-array cables, enabling a more sustainable and scalable offshore grid. Future research should focus on a comprehensive life-cycle assessment to fully evaluate the long-term environmental impact of alternative technologies.