On 15 August 2025, AEMO confirmed that Project Marinus passed the feedback loop assessment, validating its alignment with the optimal development path (ODP) in the 2024 ISP. The total cost of the project is $7.57 billion, with Stage 1 at $5.035 billion and Stage 2 at $2.535 billion.
Feedback loop confirmation allows the Australian Energy Regulator (AER) to make a determination on efficient and prudent forecast expenditure for an actionable ISP project proposed in a Transmission Network Service Provider’s contingent project application.
Project Marinus is a proposed 1,500-megawatt (MW) interconnector between Victoria and Tasmania, delivered in two 750 MW stages by Marinus Link Pty Ltd, and includes upgrades to the Tasmanian transmission network delivered by TasNetworks.
The feedback loop is the process whereby a Transmission Network Service Provider may seek confirmation from AEMO that the preferred option identified in the Regulatory Investment Test for Transmission (RIT-T) remains aligned with the optimal development path (ODP) in the most recent draft or final Integrated System Plan (ISP).
On 11 July 2025, TasNetworks requested a feedback loop assessment of Project Marinus. The letter containing the request was co-signed by Marinus Link Pty Ltd.
In undertaking the feedback loop, AEMO re-assessed the selection of the ODP identified in the 2024 ISP based on the inputs, assumptions and scenarios used to determine that ODP. This required an update of the cost benefit analysis for the 2024 ISP using the information for Project Marinus provided in the feedback loop request.
AEMO’s feedback loop assessment confirms that:
- Project Marinus addresses the relevant identified need specified, and aligns with the ODP referred to, in the 2024 ISP, and
- the total cost of the project ($7,570 million), including Stage 1 ($5,035 million) and Stage 2 ($2,535 million), does not change the status of the actionable ISP project as part of the ODP specified in the 2024 ISP.
The results of the updated cost benefit analysis and more detail on the information included in the feedback loop request are presented in a feedback loop analysis report published with the feedback loop confirmation notice.