Projected Assessment of System Adequacy (PASA)
The Projected Assessment of System Adequacy or PASA is the principal method of forecasting the adequacy of the power system to stay within the reliability standard. The National Electricity Rules requires AEMO to prepare PASA in two-time frames:
- Short Term PASA (ST PASA) covers 6 trading days from end of the trading day covered by most recent pre-dispatch schedule with a half hourly resolution; and
- Medium Term PASA (MT PASA) covers 24 months from the Sunday after the day of publication with a daily resolution.
AEMO also prepares Pre-Dispatch PASA (PD PASA) that covers the next trading interval until the end of the next trading day.
Short Term Projected Assessment of System Adequacy (ST PASA)
In May 2022, the AEMC made the National Electricity Amendment (Updating Short Term PASA) Rule 2022 (Amending Rule) to introduce greater flexibility to the short term projected assessment of system adequacy (ST PASA), revise some ST PASA definitions and obligations and require the commencement of the new ST PASA Procedure from 1 July 2025.
The ST PASA has the following objectives:
- Provide information to the market on the expected level of short-term capacity reserve and allow the market to respond to the power system needs.
- Provide a benchmark for AEMO to intervene in the market through the reserve trading provisions of the National Electricity Rules, and then commit extra capacity (either scheduled generation or loads) into the spot market.
The Reliability Standard Implementation Guidelines (RSIG) contain information on how AEMO administers ST PASA process.
For more information on the ST PASA process, please refer to the following related documents:
AEMO is currently conducting a comprehensive review of the PD and ST PASA methodology, exploring the development of a system that will serve the NEM now, and into the future.
Medium Term Projected Assessment of System Adequacy (MT PASA)
MT PASA assesses the adequacy of expected electricity supply to meet demand across the two-year horizon through regular assessment of any projected failure to meet the reliability standard. This assists Registered Participants and other stakeholders making decisions about supply, demand and transmission network outages over that period.
Each week participants must submit forecasts of availability to AEMO for the next 36 months, commencing from the first Sunday after the latest MT PASA run. These forecasts form the basis of the MT PASA report that will be produced the following week.
The MT PASA process description and the Reliability Standard Implementation Guidelines (RSIG) contain information on how AEMO administers MT PASA process.
General FAQs
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What does it mean to not provide a recall value ie ‘Null’ value or ‘Blank’ value?
Bid submission, via API:
A bidding system would reject an energy bid if, for any interval:- Recall Period attribute is defined, but its value is left blank, e.g.
- “recallPeriod”:
- Recall Period attribute is defined, but its value is non-numeric, or a string enclosed in quotes, e.g.
- “recallPeriod”: <tab key>,
- “recallPeriod”: “<space key>”,
- Recall Period attribute is defined, but its value is a null character (ascii CHR(0) )
If the Recall Period attribute is removed for an interval, bid is accepted and default value of 24000 is automatically inserted.
The following sample JSON bid is accepted
- Recall Period attribute defined in PeriodID 1 with a value of 2
- Recall Period attribute removed in PeriodIDs 2 and 3, system inserts a value of 24000 (default)
The following JSON bid is rejected, because the Recall Period attribute is defined in PeriodID 4, but its value is the null character (JSON schema validation error, ‘Invalid Type, expected Number but got Null’)
Bid submission via AEMO’s web bidding portal:
If the Recall Period cell is left blank for an interval, the Recall Period attribute is removed from the JSON submission for that interval, the bid is accepted and default value of 24000 is automatically inserted. - Recall Period attribute is defined, but its value is left blank, e.g.
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What is the bid daily energy constraint validation rule?
An energy bid is rejected if the Daily Energy Constraint ≥ registered Max Capacity x 24 hours
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When can we start entering Recall Period in our energy bids?
After AEMO implements the bidding system changes on 1 July 2025.
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When will we see the new PDPASA and STPASA DUID Availability reports?
From 31 July 2025.
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What time will AEMO implement the bidding system changes?
During business hours on 1 July 2025.
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If PASA availability entered is greater than the registered Max Capacity is there a warning to participants?
Energy bid is rejected if PASA Availability > (or exceeds) registered Max Capacity
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Recall Period is the advance notice required to realise the associated recallable capacity within the ST PASA timeframe. What does this mean?
Recallable capacity = PASA Availability – available capacity
If the Recall Period associated with the recallable capacity is less than or equal to 168 hrs (7 days, the ST PASA timeframe), AEMO can use this information to manage capacity reserves, including issuing a direction to realise this additional recallable capacity. -
Does AEMO intend to combine PD PASA and ST PASA as part of the ST PASA Procedure and Recall Period project?
PD PASA and ST PASA will not be combined as a part of the ST PASA Procedure & Recall Period project. For the future ST PASA replacement project, AEMO has not yet determined whether to combine the PD and ST PASA into one run, or to retain the separate PD and ST PASA runs. This decision will be advised to participants in a future consultation.
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During a unit outage, we assume that there is no need for the participant to reduce the Recall Period prior to every PASA run to reflect the time remaining before the unit returns from the outage. Is this correct?
Yes, AEMO would manage this.
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Does AEMO use the 'old style' bids after July 1 even for a few days?
Nothing happens to the bids submitted prior to 1 July 2025, even for trading days after 1 July 2025. The new Recall Period column will remain empty until the first bids are submitted for each trading day after the bidding system change on 1 July 2025. From 1 July 2025, AEMO advises all participants to review the PASA Availability and Recall Period in all energy bids for trading days on or after 31 July 2025.
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When will AEMO stop publishing LRC outputs to participants
From 31 July 2025, AEMO will discontinue publishing PD PASA and ST PASA outputs from LRC runs.
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The participant is not receiving data in the DUIDAVAILABILITY Tables of the new NEM Reports. What can they do?
Ensure that they are set to ACTIVE in pdrMonitor or run a query (as below) to confirm.
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Are semi-scheduled generators also required to submit energy bids in the same manner as scheduled generators?
Participants must submit PASA Availability for semi-scheduled generating units to ensure a valid energy bid. However, because AEMO does not use PASA Availability for semi-scheduled generating units, the associated Recall Period is not required to be submitted, in which case the bidding system will default to 24,000 hours which is no recall available.
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What Recall Period is required for BESS?
For a BESS, for 30-minute periods where the Available Capacity is less than PASA Availability, the time to fully charge from a fully discharged state would also be suitable as recall period. Participants can state in the rebid reason that a conservative recall period has been submitted.