TenneT develops subsea transformer concept for offshore grids, launches feasibility study tender

The Dutch/German offshore transmission system operator (TSO) TenneT is working on a concept for an offshore subsea transformer that could, according to the TSO, speed up the offshore grid expansion. At the end of June, TenneT launched a tender in Germany for feasibility studies into the concept.

According to the information in the tender notice, a subsea transformer platform technically simplifies and downsizes conventional offshore converter platforms, reducing costs.

Referred to as TenneT Offshore Subsea Transformer by the TSO, the main innovation of the concept is the relocation of components for offshore grid connection systems to the seabed. Should the technology be developed and implemented, it could complement the new 2 GW standard in offshore wind grid connection to accelerate the expansion of offshore grids, according to TenneT.

The TSO is now looking to perform feasibility studies in preparation for the potential development of offshore subsea transformers and their components.  

On June 27, TenneT launched a competitive tendering procedure for feasibility studies for the TenneT Offshore Subsea Transformer in Germany.

The tender is divided into four lots, each for a feasibility study for one element of a subsea transformer system: VSC-HVDC transformer (Lot 1), EHV submarine cable (Lot 2), reversible EHV subsea connector (Lot 3), and the installation concept (Lot 4).

The deadline for requests to participate is July 19 and the invitation to submit proposals is expected to be sent to the applicants on July 25.

TenneT did not publish details of its early concept for a subsea transformer platform.

The concept is not the first for a subsea offshore grid connection platform. In January 2024, Aker Solutions and the Marine Energy Test Centre (METCentre) in Norway announced that they signed a front-end engineering and design (FEED) contract for a pilot project testing Aker Solutions’ new power transmission technology at the METCentre’s offshore test site.

Called the Subsea Collector, Aker Solutions’ concept revolves around a subsea system that connects multiple floating wind turbines in a star configuration instead of the traditional daisy chain pattern. The technology is said to have the potential to reduce the costs of offshore transmission infrastructure by up to 10 per cent.