Historical electricity risk curves

Report notes

1. The system operator is responsible for publishing the electricity risk curves (ERCs) as part of its security of supply forecasting function. The set of ERC’s established in 1 Aug 2019 are available under the show parameter and include, risk status boundaries, percentage risk curves (these have been established the longest), contingent storage release boundaries, and official conservation campaign triggers. These various curves are produced for New Zealand and the South Island. Please see https://www.transpower.co.nz/system-operator/security-supply-and-ercs for current ERCs and further information. The system operator inherited the responsibility for forecasting security of supply from the Electricity Commission, the Electricity Authority’s predecessor, in November 2010.

2. The Authority monitors the market response to shortage. This report tracks the history of the risk of shortage in the New Zealand electricity system, as reported by the system operator.

3. Hydro data (storage and/or inflows) is sourced from NZX hydro (data provided by NIWA) and is not available for download. Please see https://energy.nzx.com for more information. In this report controlled storage in the North Island includes Lake Taupo, and in the South Island, Lakes Tekapo, Pukaki, Hawea, and Te Anau and Manapouri.

4. The framework for monitoring security of supply has evolved through time, particularly with regard to the treatment of contingent storage and the volume of available contingent storage. These changes are marked with vertical grey lines. The current set of curves have included available contingent storage from 1 August 2019. On 27 Feb 2020, following Meridian’s announcement that it could fully utilise the consented contingent storage in Lake Pukaki, storage increased by a further 367 GWh. To accurately represent the new regime and changes to available contingent storage, step changes in storage, mean storage, and maximum storage were added. The mean storage represented in the report is no longer the mean of the historical data presented in this report, but an adjusted mean to reflect the change from this point forward (i.e. without changing what was presented in the past). Prior to the 1 Aug 2019 contingent storage was excluded from the framework. A change was made on 29 August 2018 to bring the treatment of Tekapo contingent storage into line with the excluded treatment of other contingent storage as detailed in the SoSFIP. This change removed 220 GWh of Tekapo contingent storage from controlled storage over summer (denoted as 1 October – 31 March).

5. The set of electricity risk curves are updated periodically including when there is a material change to the inputs. These updates are marked with a black triangle in the figure and have occurred for the following reasons:

   • 19 Aug 2024: updated gas forecast, gas reallocation, outages, commissioning and decommissioning dates, stored gas and coal
   • 05 Sep 2024: Updated planned outages and forecast gas production
   • 20 Sep 2024: Updated Ahuroa gas storage, deratings, planned outages
   • 18 Oct 2024: updated gas produciton, storage, coal imports and stockpiles, generator commissionings and outages
   • 20 Nov 2024: Updated outages, coal and gas supply, TCC returned to service for 2025 (with limited running hours)
   • 20 Dec 2024: Updated outages and deratings - coal stockpile and AGS increase
   • 24 Jan 2025: gas production forecast, coal stockpile, gas storage, outages and commissioning dates
   • 26 Feb 2025: updated coal stockpile, gas production forecast, outages, commissionings
   • 26 Mar 2025: updated gas forecast, coal and gas storage info, outages and commissioning info
   • 23 May 2025: planned outages, deratings, methanex gas deal, rankine retirement
   • 27 Jun 2025: increae in gas production forecast, gas storage levels and coal stockpile since last month. Updates to planned generator outages and comissioning dates. Scenario where third Rankine remains.
   • 25 Jul 2025: Updated gas production forecasts, coal stockpile. Huntly rankine remains scenario
   • 25 Aug 2025: Updated outages, decreased gas forecast slightly, Huntly remains scenario
   • 25 Sep 2025: Updated commissionings and outages, deratings and scenario where third Rankine stays
   • 23 Oct 2025: Changes to commissioning dates, third Rankine included in the base case, gas production forecast and starting coal stockpile
   • 24 Nov 2025: outages, commissionings, stored thermal fuel, gas production forecast
   • 19 Dec 2025: Planned outages, gas production forecast and stored gas increased, deratings reduced
   • 28 Jan 2026: Increased gas storage, planned outages, deratings
   • 26 Feb 2026: outages, deratings, commissionings - minimal net changes to curves
   • 30 Mar 2026: industrial gas reallocation, increased gas storage, new generators
   • 28 Apr 2026: april update. ower coal and gas availability, scheduled thermal outages, commissioning dates
   • 28 May 2026: slight increase in coal stockpile and decrease in gas storage, SOSFIP updates to Watch and Alert curves, reduced gas production forecasts, slightly later commissioning of new generation
   • 26 Jun 2026: a modelling change physical gas volume accounting to use contracted volume if thats greater, slight increase in coal stockpile and increase in gas storage, reduced gas production forecasts, slightly later commissioning of new generation
   • 31 Jul 2026: outages, commissionings, detatings, contracted fuel scenario