|Risk date||Publication date||Series||Value (GWh)|
|30/06/2017||30/06/2017||HRC revised||Updated demand and generation outages. Included 2018 hydro risk curves.|
|26/07/2017||26/07/2017||HRC revised||Updated generation outages and commissioning date of Te Ahi O Maui - Included Junction Road - Revised security constraints under transmission assumptions section|
This report publishes historical hydro risk curves against controlled storage over time. Hydro risk curves are published by the system operator and indicate the probability of energy shortage to the electricity system without using any contingent storage.
The system operator is responsible for publishing the hydro risk curves (HRCs) as part of its security of supply function. HRCs are produced for New Zealand and the South Island. Please see https://www.transpower.co.nz/system-operator/security-supply/hydro-risk-curves for current HRCs and further information. This responsibility for security of supply passed from the Electricity Commission to the system operator in November 2010.
The Authority undertakes industry and market monitoring, and shortage of hydro supply can impact things such as forward price expectations and market behaviours. This report tracks the history of the risk of shortage in the New Zealand electricity system, as reported by the system operator.
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.
On 29 August 2018 the system operator adjusted the treatment of Tekapo summer (denoted as 1 October – 31 March) contingent storage to be excluded from the HRC framework. This change removes 220 GWh from controlled storage over summer for NZ and the South Island. The change has brought the treatment of Tekapo contingent storage into line with the treatment of other contingent storage and the SoSFIP. In addition to small changes to the 2019 HRCs, the controlled storage, nominal full, and mean storage have all been adjusted. The mean storage we represent in the chart is no longer the mean of the data presented, but an adjusted mean to reflect the change from this point forward (i.e. without changing what was presented in the past). This treatment helps indicate to users that there is a sudden drop (1 October) or increase (31 March) in active controlled storage of 220 GWh.
The hydro 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:
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