The Australian Energy Market Operator (AEMO) administers and operates the Wholesale Electricity Market (WEM) in the South West Interconnected System (SWIS). AEMO has identified a potential requirement to secure up to 142 MW of Supplementary Capacity (SC) over the period from 1 December 2025 to 1 April 2026. In accordance with clause 4.24 of the ESM Rules, AEMO is commencing the SC process for the 2025–26 Capacity Year.

• Tender submissions are invited for two types of SC Service:

     - Availability and Activation (A&A) Service provided by Registered Facilities and Unregistered Equipment

     - Activation-only (AO) Service provided by Unregistered Equipment only

• The maximum term of SC Contracts will be 121 days, commencing at 8AM on 1 December 2025 and ending at 8AM on 1 April 2026. Shorter contract terms may be entered into as required.

•Changes from previous Hot Season in which SC was used:

     - AEMO has a minimum service quantity of 5 MW for SC.

     - SC for the 2025-26 Capacity Year can be activated during the Service Period from 4PM to 9PM AWST on a Trading Day for A&A and AO contracts. AEMO will give preference (i.e. higher evaluation rating) to offers with a service duration of 5 hours covering the entire Service Period. However, offers with shorter durations to a minimum of 2 hours will still be considered.

     - Under the AO service, AEMO is allowing voluntary activation for up to 3 hours before and after the Service Period, which are 1PM – 4PM and 9PM - 12AM AWST (under “Extended Service Period”). Tenders that are able to offer voluntary activation during the Extended Service Period will be reviewed favourably during the tender evaluation.

• In 2023-24 Capacity Year, AEMO activated SC for a total of 70 hours during the Service Period. For the upcoming 2025-26 Hot Season, AEMO does not expect to activate SC in excess of this amount.

• Please check the link WEM Supplementary Capacity on AEMO Website for general information on Supplementary Capacity, including:

- The Standard Form Contracts

- The SC 2025-26 Tender Guidelines

- Acknowledgement Notice

- Tender Forms for A&A

- Tender Forms for AO

- Proposed NMI Spreadsheet

- Frequently Asked Questions

- Information on Excluded Transmission Node Identifiers (Excluded TNIs), for which NMIs that form part of the Unregistered Equipment in those TNI areas are excluded for the purposes of SC 2025-26

Submissions for Supplementary Capacity must be submitted via the tendering portal.

All AEMO enquiries must be directed via AEMO’s eSourcing tool.

For assistance, please contact the WA Registration, Monitoring and Procurement team at supplementary.capacity@aemo.com.au.

Western Power enquiries must be directed to network.access@westernpower.com.au.

The WEM Procedure: Supplementary Capacity can be located here: https://aemo.com.au/energy-systems/electricity/wholesale-electricity-market-wem/procedures-policies-and-guides/procedures

ESM Rules relevant to the Supplementary Capacity process can be found at: https://www.wa.gov.au/government/document-collections/electricity-system-and-market-rules