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 Jul 2021: Updated outages for the next 8 months. Thermal deratings updated following changes to coal stockpile information. Demand adjusted to remove Norkse Skog load.
   • 19 Aug 2021: Updated outages for the next 8 months. Thermal deratings updated.
   • 24 Sep 2021: Updated planned outages for next 8 months. Thermal deratings updated with gas storage update. This month we also made some technical modelling changes that have had negligible effect on the ERC values but we feel provide improved modelling confidence. These were to change wind generation to be modeled on actual 40 years of actual wind data, similar to the treatment of inflows. Where insufficient data is available wind reverts to a profiled output. We also made a change to treatment of forced outages for geothermal generation and a change to the thermal fuel dispatch order.
   • 25 Oct 2021: Update outages and thermal deratings. Maximum output of Ngawha B was increased slightly to better reflect reality.