ST PASA Replacement

Overview

The Australian Energy Market Operator (AEMO) commenced the ST PASA Replacement project in 2019 with the intention of modernising the systems and processes supporting the Short-Term Projected Assessment of System Adequacy (ST PASA) for the National Electricity Market (NEM). This assessment plays a crucial role in forecasting reliability risks for the NEM's electricity system over a seven-day period. By implementing these system improvements, AEMO seeks to provide more detailed and accurate insights into the adequacy of the power system. These enhancements are designed to support improved operational decision-making, increase transparency within the electricity market, and strengthen the overall reliability and security of the NEM.

The Pre-Dispatch PASA (PD PASA) and ST PASA systems are pivotal tools used by AEMO and electricity sector participants to identify and manage risks to power system security and reliability in the upcoming seven days. While these systems share broad similarities, they differ in terms of their forecasting horizons and publication frequency. Their original design catered to a NEM dominated by large thermal generation units connected to the transmission grid.

Recent assessments of the PD PASA and ST PASA systems have revealed several limitations. The energy landscape is undergoing rapid transformation, fuelled by the emergence of new technologies such as battery storage, virtual power plants (VPPs), and distributed energy resources (DER). Existing PD PASA and ST PASA frameworks lack the capacity to accurately model these innovations. They also fall short in representing intra-regional network constraints, sharing reserves across regions, and adequately reflecting energy-limited resources.

In response to these challenges, AEMO is undertaking a comprehensive redevelopment of the PD PASA and ST PASA systems. This redevelopment aims to ensure the systems remain fit for purpose and continue to support the evolving needs of the energy sector.

Engagement with industry stakeholders is fundamental to the success of the ST PASA Replacement initiative. This collaborative approach ensures that the project's outcomes are aligned with both operational needs and market expectations. Progress is already underway, with two rounds of consultations addressing a new ST PASA Procedure and a new Reserve Level Declaration Guideline. The first round of consultation concluded in October 2025, while the second round is scheduled to be finalised in July 2026. By incorporating the remaining scope of the ST PASA Replacement within the NEM Reform Implementation Roadmap, AEMO is positioning this initiative as an integral part of the broader NEM Reform Program. This strategy offers market participants a coordinated and holistic perspective on industry changes.

Procedure changes

Certain procedures, guidelines, and other documents maintained by AEMO require updating to facilitate the implementation of the ST PASA Replacement. For further details regarding the affected documents, please consult the most recent consultations by reviewing the links provided below.

Industry Engagement

Since 2020, AEMO has conducted structured industry engagement to facilitate comprehensive evaluation of the technical aspects of the ST PASA Replacement project. This initiative aims to collect valuable insights into the utilisation of PD and ST PASA information and to identify emerging requirements for these systems. The consultation process has included targeted workshops, where challenges and anticipated needs have been discussed with industry stakeholders. Presentation materials, summaries, and reports from these engagements are provided below. Engagement remains ongoing, and AEMO will continue collaborating with industry through the NEM Reform Program forums and committees.

Reference information

For more information, please contact [email protected] or visit the NEM Reform Program webpage.