Tender for Supplementary Capacity 2025-26 – WEM

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.
• 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 is seeking service duration of 5 hours with a minimum of 5 MW of capacity. Lower service durations and minimum service quantities may be considered at the discretion of AEMO.
• 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 WEM Supplementary Capacity for the Excluded Transmission Node Identifiers (Excluded TNIs). These are excluded solely for the purposes of SC 2025-26.

For further details please see a copy of the Tender Guidelines below.

Submissions for Supplementary Capacity must be submitted via the VendorPanel by 12pm AWST on Monday 15 September 2025.

The key activities of the 2025-26 Supplementary Capacity tender are outlined below:

For assistance, please contact the WA Registration, Monitoring and Procurement team at [email protected]

Western Power enquiries must be directed to [email protected]

WEM Procedure

The WEM Procedure for Supplementary Capacity can be found here:  AEMO | WEM Procedures