What is FCAS? The ten FCAS markets in the NEM, explained

What FCAS (frequency control ancillary services) is in the Australian NEM, the ten FCAS markets, how they are priced, and why batteries earn so much from them.

FCAS stands for frequency control ancillary services. It is a set of markets AEMO runs next to the energy market to hold the grid's frequency close to 50 Hz, inside a normal operating band of 49.85 to 50.15 Hz. Frequency moves whenever generation and demand fall out of balance. If it moves too far, equipment trips, and in the worst case the system blacks out. FCAS is how AEMO buys the fast response that stops that happening.

There are ten FCAS markets

Each one clears every five minutes with its own price, alongside energy. They fall into two families.

• Eight contingency markets: 1-second, 6-second, 60-second and 5-minute response, each in a raise and a lower direction. They sit in reserve and only call on capacity when something sudden happens, like a large generator or transmission line tripping. The 1-second markets are the newest, starting in October 2023.
• Two regulation markets: raise and lower. These run continuously. An enabled unit follows AEMO's automatic generation control signal and nudges its output up or down every few seconds to correct the small, constant drift of normal operation.

FCAS pays for being ready, not just for acting

FCAS prices are quoted in dollars per megawatt per hour. A unit is paid for the capacity it holds available in each market, whether or not AEMO ever calls on it, with a further payment if it is actually dispatched. That structure is why FCAS can be a steady earner even when the energy market is quiet.

It is also lumpy. Contingency prices can spike when the system is tight or islanded, and South Australia is the usual example. When the markets are well supplied they can collapse to a few cents.

Batteries are close to ideal for it

A battery can inject or absorb full power within milliseconds, much faster than thermal plant, and can swap between charging and discharging without penalty. Most grid-scale batteries in the NEM sit enabled in one or more contingency markets almost all the time. That makes raw enablement a weak signal of strategy. A better one is how much of a battery's capacity is reserved for FCAS on average, which is what separates an FCAS-primary unit from an arbitrage-primary one.

The catch is that FCAS and arbitrage compete for the same megawatts

Every megawatt a battery reserves for FCAS is a megawatt it cannot use for energy arbitrage in that interval. Finding the best split, market by market and interval by interval, is the co-optimisation problem the NEMPulse optimal-dispatch benchmark solves.

Regulation also changed in June 2025, when AEMO introduced frequency performance payments. Units now earn or lose money depending on how closely they track the control signal, so regulation is no longer just a capacity payment. See the FPP entry in the glossary for how NEMPulse reports it.

Where to see it on NEMPulse

Each battery page breaks FCAS revenue out by market, and the performance page compares what each unit actually earned in FCAS with what the optimal benchmark would have earned.

More guides: How does a grid-scale battery make money in the NEM?What is capture rate? Benchmarking battery performance

See also: FCAS — glossaryContingency FCASRegulation FCASFPP schemeBattery fleet and FCAS revenue

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