The automatic change in a generator's output as frequency moves. A 2020 rule made narrow-band PFR mandatory for most large generators.
The terms used on our live price pages and across Australian energy projects, explained in a sentence or two each.
- National Electricity Market (NEM)
The wholesale electricity market and interconnected power system covering Queensland, New South Wales, Victoria, South Australia and Tasmania, including the ACT. Western Australia and the Northern Territory run separate systems.
- AEMO
The Australian Energy Market Operator. It runs the NEM, dispatches generation every 5 minutes, publishes the market data these pages use, and manages power system security.
- Region
The NEM is split into five pricing regions, QLD1, NSW1, VIC1, SA1 and TAS1, each with its own price. They roughly follow state borders; the ACT sits in NSW1.
- Regional reference price (RRP)
The wholesale energy price for a region in a dispatch interval, in dollars per megawatt-hour. It is the number on our live price cards.
- Dispatch interval
The 5-minute period for which AEMO sets generator targets and prices. Intervals are labelled by the time they end, so the 10:05 interval runs from 10:00 to 10:05.
- Five-minute settlement
Since 1 October 2021 generators are paid and retailers charged at the 5-minute dispatch price, rather than at a 30-minute average.
- NEMDE
The NEM Dispatch Engine, the optimisation software that matches offers to demand every 5 minutes, sets prices, and co-optimises energy with FCAS.
- Operational demand
The demand met by scheduled, semi-scheduled and significant non-scheduled generation. Rooftop solar reduces it, which is why it can fall very low, or even below zero, in South Australia at midday.
- Negative price
A price below $0/MWh, where generators pay to keep running. It happens when supply, often solar, exceeds demand and some plant would rather pay than turn off. See negative price hours.
- Market price cap
The highest price the NEM can reach in an interval, reset each financial year. It applies to energy and FCAS.
- Market floor price
The lowest price the NEM can reach, -$1,000/MWh.
- Cumulative price threshold (CPT)
A limit on the sum of prices over a rolling seven days. If it is exceeded, an administered price cap applies until prices fall back.
- Administered price cap (APC)
A temporary cap that replaces the market price cap after the cumulative price threshold is breached. Our cards flag an interval when it applies.
- Market suspension
When AEMO suspends the market, for example in June 2022, prices are set by a schedule rather than by offers. Our cards flag a suspended interval.
- Interconnector
A transmission link between two regions, such as Heywood between Victoria and South Australia or Basslink between Victoria and Tasmania. When an interconnector is full, regional prices separate.
- Net interchange
The net flow of power into or out of a region across its interconnectors. Our cards show it as importing or exporting.
- Price status (FIRM, NOT FIRM)
AEMO marks a price NOT FIRM while it can still be reviewed, and FIRM once confirmed. Most prices are firm within minutes.
- FCAS
Frequency control ancillary services, bought in ten markets to keep frequency near 50 hertz. See live FCAS prices.
- Regulation FCAS
Raise and lower services that correct small, continuous frequency deviations by following AEMO control signals.
- Contingency FCAS
Raise and lower services held ready for a large, sudden event, split by speed of response into 1-second, 6-second, 60-second and 5-minute markets.
- Enablement
The amount of FCAS capacity, in megawatts, that AEMO selects a unit to hold ready in an interval. FCAS is paid on enablement, at $/MW/h.
- Local FCAS requirement
A requirement that a region source some FCAS from within itself, set when it could be islanded. It is the usual reason one region's FCAS price differs from the others.
- Frequency performance payments
The arrangement, in place since 8 June 2025, that allocates regulation FCAS costs by how each unit's behaviour helps or harms frequency.
- Primary frequency response (PFR)
- Inertia
The energy stored in the spinning mass of synchronous machines, which slows how fast frequency changes after a disturbance. Falling inertia is one reason the 1-second FCAS markets were created.
- System strength
The ability of the network to hold voltage steady during faults, which inverter-based plant such as solar, wind and batteries needs.
- Marginal loss factor (MLF)
A number that scales a generator's revenue for the electrical losses between its connection point and the regional reference node. It is set each year. See MLF and curtailment risk.
- Curtailment
Output a generator could have produced but did not, because of network limits, negative prices or AEMO instructions.
- Semi-scheduled generator
A generator with variable output, typically wind or solar over 30 MW, that must follow AEMO dispatch caps but is not required to offer a fixed output.
- Energy arbitrage
Charging a battery when prices are low and discharging when they are high, earning the spread. See how BESS make money.
- Intervention
When AEMO directs a unit or activates reserves to keep the system secure, dispatch runs twice. The prices shown on these pages come from the pricing run, intervention flag 0.
- Large-scale generation certificate (LGC)
A certificate for one megawatt-hour of electricity from an accredited renewable power station, created under the Renewable Energy Target until the end of 2030. See LGC and STC prices.
- Small-scale technology certificate (STC)
A certificate created when rooftop solar, a solar water heater, a heat pump or a home battery is installed, worth up to $40 through the STC clearing house. See LGC and STC prices.
- Renewable power percentage (RPP)
The share of the electricity a liable entity buys in a year for which it must surrender LGCs, set each year by the Clean Energy Regulator.
- Guarantee of Origin (GO)
The Australian scheme, run by the Clean Energy Regulator, that certifies where electricity and other products come from. It continues after the Renewable Energy Target ends in 2030.
Missing a term? These definitions are kept short on purpose. For the full picture of how the market works, read the National Electricity Market explained, or get in touch with our engineers about your project.