FCAS encompasses eight markets, each designed to respond to specific frequency deviations or system events. These services differ in the speed, direction of response required, and the method of control, which in turn shape the technical standards a device or aggregated portfolio must meet to participate.

To provide FCAS, a participant must be registered with AEMO and classify the relevant technology, whether a generating unit, load, BESS, or an aggregated CER portfolio, as an ASU or ASF. An ASU is an individual unit (e.g., generator, battery inverter) that delivers an ancillary service, while an ASF is the registered facility grouping of one or more ASUs for market participation under a single participant.

This process establishes the plant’s eligibility to offer FCAS and confirms compliance with the MASS, including performance verification, metering accuracy, telemetry and response characteristics. Once registered, the participant can offer services into the relevant FCAS markets through the standard bidding and dispatch processes used across the NEM.

Key points

• The NEM has eight FCAS markets: four response speeds, each with Raise and Lower services.
• Contingency FCAS responds automatically to sudden frequency disturbances.
• Regulation FCAS continuously adjusts generation or load through AEMO’s automatic generation control system.
• Participants must register eligible ancillary service units and facilities with AEMO.
• Resources must comply with the Market Ancillary Service Specification, including measurement and performance requirements.
• Aggregated CER already participates in contingency FCAS, while regulation participation involves more complex control and telemetry requirements.

Types of FCAS

FCAS services in the NEM are grouped into two broad categories, Contingency FCAS and Regulation FCAS, each designed to stabilise system frequency under different operating conditions. Within both categories, participants may offer FCAS Raise services (increasing generation or reducing load) or FCAS Lower services (reducing generation or increasing load), depending on whether the system requires upward or downward correction.

Contingency FCAS

Contingency FCAS is delivered automatically in response to locally measured frequency disturbances, such as the sudden loss of generation or load. When enabled for a dispatch interval, an ancillary service provider must deliver its enabled quantity automatically whenever local frequency moves outside the relevant deadband specified in the MASS. This activation is triggered by the facility’s own frequency measurement rather than by a signal from AEMO.

Contingency FCAS markets are divided by response speed and direction, with each market including both FCAS Raise and FCAS Lower services:

• Very Fast (1 second): Must deliver at least 50% of the enabled volume within the first second after a frequency event, for both FCAS Raise and FCAS Lower services.
• Fast (6 seconds): Must deliver the full enabled response within 6 seconds, for both FCAS Raise and FCAS Lower services.
• Slow (60 seconds): Must deliver the full enabled response within 60 seconds, for both FCAS Raise and FCAS Lower services.
• Delayed (5 minutes): Must deliver the full enabled response within 5 minutes, for both FCAS Raise and FCAS Lower services.

Each market has defined performance obligations to ensure rapid and reliable frequency control, with requirements tailored to the speed and direction of response needed.

Regulation FCAS

Regulation FCAS supports continuous control of system frequency under normal operating conditions. Unlike Contingency FCAS, Regulation FCAS is centrally coordinated through AEMO’s automatic generation control (AGC) system, which adjusts each participating unit's output or load in real time to keep frequency close to 50 Hz.

Two separate markets, Regulation Raise and Regulation Lower, operate to manage upward and downward balancing needs. Participation requires high-speed telemetry (minimum 4-second resolution) and the capability to follow AGC setpoints via an ICCP or equivalent high-speed data link, which results in more complex integration requirements than for Contingency FCAS.

CER FCAS participation

CER currently plays a meaningful role in Contingency FCAS, particularly through flexible loads and aggregated demand response, which collectively form a large share of available market capacity. By contrast, Regulation FCAS participation by aggregated CER portfolios is considered an emerging use case not yet adopted. While individual small batteries or loads may technically participate if classified as a scheduled unit, aggregated CER cannot provide regulation services due to the absence of an approved telemetry and AGC integration pathways for portfolios.

This gap is expected to narrow under the future reforms and VPPs registering as VSRs may become eligible to offer Regulation FCAS. However, the detailed performance, control and compliance requirements for aggregated CER participation have not yet been developed and will be clarified through future AEMO procedures and industry implementation work.

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