FCAS, reserves and system security

The question

Can the same unit offer its maximum FCAS at every energy output?

Mechanism

A service capability curve uses enablement minimum, low breakpoint, high breakpoint, enablement maximum and maximum availability. Within a simplified trapezium, the available service rises along the lower edge, stays flat between breakpoints, and falls along the upper edge. This links energy output to service capability.

For our teaching unit use minimum 10, low 30, high 70 and maximum 100 MW, with maximum reserve 40 MW. This is a fixed-energy, single-service illustration. Real dispatch also applies joint constraints, service-specific parameters, ramping and other requirements.

Calculate both sloping edges and the flat maximum, then take the non-negative minimum. A stated 40 MW maximum is not an instruction to enable 40 MW everywhere. Outputs outside the enablement range produce zero service in this model.

Worked numbers

At 20 MW energy: 40 × (20 − 10)/(30 − 10) = 20 MW. At 60 MW: 40 MW. At 80 MW: 40 × (100 − 80)/(100 − 70) = 26.67 MW before shared headroom.

Try it in the workspace

Select the Low edge and High output scenarios. Predict capability before revealing the results.

The question

Which restriction actually limits the reserve offer?

Mechanism

At a fixed energy output, the teaching desk applies both the trapezium and a shared nameplate headroom limit. Unit A's usable reserve is the smaller of those two values. The second provider has separately specified available reserve; the desk does not infer its energy schedule.

At 80 MW energy and 100 MW physical availability, headroom is 20 MW. Although the trapezium permits 26.67 MW, the combined bound permits only 20 MW. Reducing energy can create headroom, but it may move the unit down the other side of the trapezium. More headroom alone does not guarantee more FCAS.

The desk holds energy fixed and buys the cheaper reserve first. It is not a co-optimiser: it does not trade energy redispatch against FCAS procurement cost. Return to Topic 14 for that opportunity-cost mechanism, then identify which joint constraints a production model would need.

Worked numbers

Base energy 60: A supplies 40 MW at A$5/MW/h and B supplies 10 at A$20/MW/h. Offer cost is A$400/h. At energy 80, A supplies 20 and B supplies 30: A$700/h.

Try it in the workspace

Change energy from 60 to 80 MW with reserve demand fixed at 50. Identify the extra provider and the A$300/h cost change.

The question

How much does one additional MW of required reserve cost?

Mechanism

Once cheaper reserve has been used, an additional requirement is supplied by the next feasible provider. The desk resolves the fixed-energy allocation for requirement plus one MW. Its cost difference is a finite incremental cost under the displayed assumptions.

In the base case, A is already at 40 MW capability and B supplies 10. An extra MW comes from B at A$20/MW/h. The average procurement cost is A$400/50 = A$8/MW/h; it does not determine the incremental cost. Neither figure is claimed to be a published NEM FCAS price.

If the requirement exceeds total capability, show a shortfall and withhold the marginal-price interpretation. A penalty could make an optimisation model solvable mathematically, but it would not create a physical response. Near a breakpoint, a finite one-MW step can straddle more than one marginal segment.

Worked numbers

Base cost A$400/h; requirement 51 MW costs A$420/h. At energy 80 with only 5 MW from B, a 50 MW requirement leaves 25 MW unavailable.

Try it in the workspace

Select Reserve shortfall. Explain why the desk displays no feasible incremental cost rather than inventing an FCAS price.

The question

Does an LOR notice mean load is already being shed?

Mechanism

Lack-of-reserve notices describe reserve conditions across the operational horizon. Read the region, forecast or actual status, period, threshold and update time. A forecast notice is not evidence that customers have already lost supply.

Short-term reserve assessment accounts for credible contingencies and forecast uncertainty. It is not simply 'installed MW minus demand', nor can an analyst apply a single fixed percentage to every interval. A service-capability shortfall in our desk does not calculate an LOR level.

RERT uses contracted emergency reserve under its own eligibility, procurement and activation arrangements. It is not one of the ten FCAS markets, and an LOR notice does not prove RERT has been activated. Keep reserve condition, operational decision and observed outcome in separate columns.

Worked numbers

Illustrative screening only: 900 MW available against 850 MW demand leaves 50 MW before contingency and uncertainty requirements. That subtraction alone cannot classify LOR or establish security.

Try it in the workspace

Write a three-row evidence ledger: forecast notice, intervention decision, measured outcome. State which source verifies each row.

The question

What can five regional price records tell us?

Mechanism

The evidence lab reads the preserved AEMO DISPATCH/PRICE v5 header and five records for 18 October 2026, 12:45 market time. It selects intervention=0 and exposes ten FCAS price fields with price-status and administered-pricing/suspension flags. These are dated observations, not a current feed.

Start with NSW1: the published raise-regulation price is 1.44; the very-fast raise price is 0.01. For an explicitly hypothetical 12 MW enabled throughout five minutes, the unadjusted service-value illustrations are A$1.44 and A$0.01 respectively. The chosen 12 MW is not an observed unit enablement.

To reconstruct real earnings, obtain matching unit-level enablements and applicable service, region, run, interval, revisions and settlement rules. Do not apply all ten prices to the same MW without proving simultaneous feasible capability and the applicable treatment.

Worked numbers

12 × 5/60 × 1.44 = A$1.44; 12 × 5/60 × 0.01 = A$0.01. The common multiplier equals one MW·h, not one MWh of measured response.

Try it in the workspace

Load the real snapshot in Apply it, choose NSW1 and compare the two fields. Export the evidence record and list the missing unit data.

The question

Which version of a technical document governs the interpretation?

Mechanism

MASS v8.2 and the FCAS Model in NEMDE v3.0 are both effective 3 June 2024 in the current official register. Very-fast FCAS began in October 2023, but local requirements and transitional limits have continued to change. A launch-date fact is not a timeless operating limit.

The AEMO very-fast transition page includes local updates from June 2026. Do not preserve an old universal 50 MW limit in a model as if it applies everywhere today. Read location, islanding condition, service direction and commencement before using a listed limit.

Finish with a versioned recommendation: what the fixed-energy model establishes, which actual prices were observed, and what would require a full joint-dispatch or compliance review. This course does not authorise market offers or certify delivery performance.

Worked numbers

A hypothetical 12 MW enablement remains a modelling assumption even when paired with a genuine published price. Replacing a price source does not validate the other inputs.

Try it in the workspace

Compare your exported evidence record with the source register. Check schema version, interval, service name and the date due for review.