Who operates Wholesale Electricity Market (WEM)?

Australian Energy Market Operator (AEMO) operates Wholesale Electricity Market (WEM), covering Western Australia: South West Interconnected System.

Was a qualifying capacity event held in Wholesale Electricity Market (WEM) in 2025?

No. Reserve Capacity Mechanism: no qualifying 2025 event is recorded. No capacity auction for this market was found to have been held during 2025 in the sources reviewed.

How is energy traded, priced and settled in Wholesale Electricity Market (WEM)?

Wholesale Electricity Market (WEM): Bilateral-contract market with a real-time security-constrained dispatch market. Since 1 October 2023, the Real-Time Market co-optimises energy and Frequency Co-optimised Essential System Services (FCESS).

Wholesale Electricity Market (WEM)

Where energy trades

Where does energy trade in Wholesale Electricity Market (WEM)?

Energy in Wholesale Electricity Market (WEM) trades in 3 layers: real-time energy, short-term energy market and bilateral contracts.

What a battery can sell

What ancillary services can a battery sell in Wholesale Electricity Market (WEM)?

Wholesale Electricity Market (WEM) has 5 ancillary-service products, across 4 families — regulation, contingency reserve, inertia & system strength and emergency control: Contingency Reserve Lower, Contingency Reserve Raise, Regulation Lower, Regulation Raise, Rate of Change of Frequency Control Service. Response timing, direction and eligibility for each are in the table below; a product's full record lists the official sources behind it.

Every value below comes from the official sources listed in that product's full record. Most products cite more than one, and the published sources do not say which of them states each individual value, so the binding is to the product's record rather than to a single document. A missing line means the source does not state that value — never that the value is zero.

Scroll the table sideways for the rest of the columns →

5 ancillary-service products in Wholesale Electricity Market (WEM), grouped into 4 families. Each row runs left to right through one product's life: how it activates, how quickly it has to respond, how long it has to keep delivering, and how it is bought.
Service	How it activates	Response	Sustained delivery	Procurement
Regulation
Regulation Lower REG_LOWER lower generation; raise load operational	Response type pre-fault centrally controlled AGC Trigger AEMO AGC desired-MW signal; no fixed public frequency threshold.	Expected within 5 s		As stated AEMO calculates interval-specific requirements. AEMO calculates interval-specific requirements. Through co-optimised real-time FCESS market Bought real-time dispatch; forward schedules extend up to one week How it settles Real-time market enablement and dispatch settlement under ESM Rules.
Full record for Regulation Lower — document bound, page for these figures not recorded What it is for Frequently adjust injection or withdrawal under central control to lower SWIS frequency toward the Frequency Operating Standard. In force from 1 October 2023 Who can provide it AEMO-accredited facilities meeting AGC, SCADA, communication and performance requirements. Notes from the source Five seconds is maximum communication/control response lag, not full activation. Full activation and hold depend on accredited capability and dispatch. Checkpoint recap Expected within 5 s What the source does not state The source states the response deadline and a procurement volume in its own words. It does not state how long delivery has to be sustained. Sources Service specification Summary of Frequency Co-optimised Essential System Services (opens in a new tab) AEMO · may not open directly — the host restricts access Rules WEM Procedure: Frequency Co-optimised Essential System Services Accreditation v2.0 (opens in a new tab) AEMO · published 1 April 2024
Regulation Raise REG_RAISE raise generation; lower load operational	Response type pre-fault centrally controlled AGC Trigger AEMO AGC desired-MW signal; no fixed public frequency threshold.	Expected within 5 s		As stated AEMO calculates interval-specific requirements under the ESS Quantities Procedure. AEMO calculates interval-specific requirements under the ESS Quantities Procedure. Through co-optimised real-time FCESS market Bought real-time dispatch; forward schedules extend up to one week How it settles Real-time market enablement and dispatch settlement under ESM Rules.
Full record for Regulation Raise — document bound, page for these figures not recorded What it is for Frequently adjust injection or withdrawal under central control to raise SWIS frequency toward the Frequency Operating Standard. In force from 1 October 2023 Who can provide it AEMO-accredited facilities meeting AGC, SCADA, communication and performance requirements. Notes from the source Five seconds is the maximum communication/control response lag from receipt of the AEMO signal, not a universal full-ramp deadline. Full activation and hold depend on accredited ramp capability and dispatch. Checkpoint recap Expected within 5 s What the source does not state The source states the response deadline and a procurement volume in its own words. It does not state how long delivery has to be sustained. Sources Service specification Summary of Frequency Co-optimised Essential System Services (opens in a new tab) AEMO · may not open directly — the host restricts access Rules WEM Procedure: Frequency Co-optimised Essential System Services Accreditation v2.0 (opens in a new tab) AEMO · published 1 April 2024
Contingency reserve
Contingency Reserve Lower CR_LOWER lower generation; raise load operational	Response type post-fault automatic local frequency Trigger Automatic frequency-sensitive response after a contingency; facility-specific settings are accredited.		Minimum obligation at least 15 min	As stated Dynamic requirement under the ESS Quantities Procedure. Dynamic requirement under the ESS Quantities Procedure. Through co-optimised real-time FCESS market Bought real-time dispatch; supplementary procurement possible How it settles Real-time FCESS enablement settlement.
Full record for Contingency Reserve Lower — document bound, page for these figures not recorded What it is for Hold rapid downward response to contain frequency after a credible over-frequency contingency. In force from 1 October 2023 Who can provide it AEMO-accredited facilities meeting contingency response tests. Notes from the source No single market-wide full-activation deadline; accredited response capability applies. Sustain requirement is at least 15 minutes. Checkpoint recap Minimum sustained 15 min What the source does not state The source states a minimum delivery period and a procurement volume in its own words. It does not state a response time or a maximum duration. Sources Service specification Summary of Frequency Co-optimised Essential System Services (opens in a new tab) AEMO · may not open directly — the host restricts access Service specification Guideline: Frequency Co-optimised Essential System Services Testing v1.0 (opens in a new tab) AEMO · published 15 October 2021 · may not open directly — the host restricts access Service specification Contingency Reserve Quantities (opens in a new tab) AEMO · may not open directly — the host restricts access
Inertia & system strength
Rate of Change of Frequency Control Service ROCOF symmetric operational	Response type post-fault inherent or grid-forming Trigger Inherent instantaneous response to RoCoF following a disturbance; no dispatch trigger threshold.	Full activation 0 s	Not applicable a sustained-delivery duration does not apply	Requirement is expressed through system inertia/RoCoF constraints, not a stable MW volume. Through co-optimised FCESS market Bought real-time co-optimisation How it settles Real-time FCESS settlement under the ESM Rules.
Full record for Rate of Change of Frequency Control Service — document bound, page for these figures not recorded What it is for Provide inertia or inertia-equivalent capability that limits the initial rate of change of SWIS frequency after a contingency. In force from 1 October 2023 Who can provide it Facilities accredited for synchronous inertia or qualifying equivalent response under ESM Rules and procedures. Notes from the source The service is procured as inertia contribution rather than an activated MW step; a conventional sustain-duration field is not applicable. Checkpoint recap Full activation 0 s What the source does not state The source states the full-activation requirement and that a sustained-delivery duration does not apply to it. It does not state a standing procurement volume. Sources Service specification Summary of Frequency Co-optimised Essential System Services (opens in a new tab) AEMO · may not open directly — the host restricts access Rules WEM Procedure: Frequency Co-optimised Essential System Services Accreditation v2.0 (opens in a new tab) AEMO · published 1 April 2024
Emergency control
Contingency Reserve Raise CR_RAISE raise generation; lower load operational	Response type post-fault automatic local frequency Trigger Automatic frequency-sensitive response after a contingency; facility-specific droop/block settings are accredited.		Minimum obligation at least 15 min	As stated Dynamic Frequency Control Model quantity based on credible contingency size, inertia and facility performance. Dynamic Frequency Control Model quantity based on credible contingency size, inertia and facility performance. Through co-optimised real-time FCESS market Bought real-time dispatch; supplementary procurement possible How it settles Real-time FCESS enablement settlement, performance-factor adjusted where applicable.
Full record for Contingency Reserve Raise — document bound, page for these figures not recorded What it is for Hold rapid upward response to contain frequency after a credible contingency and avoid under-frequency load shedding. In force from 1 October 2023 Who can provide it Accredited generation, storage or interruptible load; minimum certified response and technical tests apply. Notes from the source No single market-wide full-activation deadline. Accreditation assigns a Facility Speed Factor from accepted bands 0.2, 0.5, 1, 3, 6, 10 or 15 seconds; the response must be sustainable for at least 15 minutes. Checkpoint recap Minimum sustained 15 min What the source does not state The source states a minimum delivery period and a procurement volume in its own words. It does not state a response time or a maximum duration. Sources Service specification Summary of Frequency Co-optimised Essential System Services (opens in a new tab) AEMO · may not open directly — the host restricts access Service specification Guideline: Frequency Co-optimised Essential System Services Testing v1.0 (opens in a new tab) AEMO · published 15 October 2021 · may not open directly — the host restricts access Service specification Contingency Reserve Quantities (opens in a new tab) AEMO · may not open directly — the host restricts access

Getting paid to exist

Does Wholesale Electricity Market (WEM) have a capacity mechanism?

Yes — Reserve Capacity Mechanism is a central capacity market.

Reserve Capacity Mechanism

operational

AEMO determines Peak and Flexible Reserve Capacity Requirements, certifies facilities, assigns Capacity Credits and pays formula/administratively determined Reserve Capacity Prices for a future Capacity Year. Bilateral trade declarations and security obligations apply.

Auction held in 2025: No — No capacity auction for this market was found to have been held during 2025 in the sources reviewed.

The 2025 Reserve Capacity Cycle produced capacity-credit and price outcomes but was not a competitive clearing auction, so it is not counted as one here.

Caveats

Technical notes

Five FCESS products are co-optimised in real time; supplementary procurement may be triggered where market supply is insufficient.

Where this comes from

Official sources

Rules

Service specification

Market explainer

WEM Dispatch Engine and Real-Time Market implementation AEMO

Capacity-mechanism explainer

Reserve Capacity Mechanism Review Government of Western Australia, Energy Policy WA
WA Electricity Consultative Forum papers: 2025 Reserve Capacity Cycle headlines AEMO

Current as of 2 August 2026 · from the Global Electricity Market Catalogue v1.2.0 (compiled to 4 August 2026, CC BY 4.0, rendered here with wording edited for readability). Facts belong to the linked official authorities; verify the current rules before design or bidding decisions.

Questions

Common questions about Wholesale Electricity Market (WEM)

Who operates Wholesale Electricity Market (WEM)?: Australian Energy Market Operator (AEMO) operates Wholesale Electricity Market (WEM), covering Western Australia: South West Interconnected System.
Was a qualifying capacity event held in Wholesale Electricity Market (WEM) in 2025?: No. Reserve Capacity Mechanism: no qualifying 2025 event is recorded. No capacity auction for this market was found to have been held during 2025 in the sources reviewed.
How is energy traded, priced and settled in Wholesale Electricity Market (WEM)?: Wholesale Electricity Market (WEM): Bilateral-contract market with a real-time security-constrained dispatch market. Since 1 October 2023, the Real-Time Market co-optimises energy and Frequency Co-optimised Essential System Services (FCESS).

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