System events and assessments

Operational impacts of low Southland generation

With storage levels at Te Anau and Manapouri low and inflows expected to be low over the coming weeks, operating restrictions at low levels could reduce generation availability and flexibility in Southland (Grid Zone 14) and areas in the short term.

The reduced generation can lead to system security issues, but these are manageable through our planned actions and we expect no effect on consumer’s electricity supply.  

The System Operator engineering assessments, reasons and planned mitigation approach can be found here, along with a link to our Customer Advice Notice informing industry of our planned approach. This approach was last used in 2022 under similar circumstances, and our studies show that it still an appropriate course of action this year.

The System Operator is asking participants to provide any other information they have that would allow us to manage this situation. We are also asking for any information or analysis of the potential costs or benefits of our proposed temporary grid reconfigurations, or of alternative reconfigurations.  

Please send any information to System.operator@transpower.co.nz  by 5pm Wednesday 5 March. 

Preparing for possible grid reconfigurations

We are getting prepared if grid reconfigurations are needed to reduce the generation requirement in order to maintain system security. In the immediate term some planned grid outages are at risk of being rescheduled, delayed, or cancelled. 

We have published here our system studies and the grid reconfiguration we will consider if storage continues to fall. We will also publish all other relevant information here so please bookmark the page or subscribe for updates. 

The following document has been updated to take into account the announcement by Meridian Energy and New Zealand Aluminium Smelters on 25 February 2025 to make an extra 50 megawatts of electricity available over winter.

Enhanced Security of Supply Activities

A combination of below average inflows in Aotearoa’s hydro generation catchments, constraints in the gas market, high electricity demand in May and low wind generation contributed to a rapid decline in hydro storage over winter.

By mid-August, hydro lake levels were just 51% of average for the time of year, which is among the lowest levels we have reached in around 90 years of historic records. We stepped up our security of supply reporting as a result and worked closely with industry, government and other stakeholders to monitor and manage the situation.

With New Zealand hydro storage rebounding to 109% of average for the time of year by late September, we ceased these enhanced security of supply activities. More information about our approach to the situation can be found here.

Northland Loss of Supply, 20-23 June 2024

Transpower, in its role as system operator, has published its independent investigation into the loss of electricity supply to Northland from 20-23 June 2024. The investigation was commissioned by Transpower as per its system operator procedures for reporting significant incidents.

The investigation focused on the operational performance of Transpower in its dual system operator and grid owner roles as well as industry participants leading up to and in response to the event. It did not investigate the tower failure that caused the outage, which was addressed in a separate investigation published on 1 August 2024.

The independent report is published alongside our response to the recommendations and our preliminary report that was published on 5 July 2024.

Gannon Geomagnetic Storm

A series of powerful solar storms with extreme solar flares and geomagnetic storm components occurred from 10–13 May 2024. The resulting geomagnetic storm “Gannon” was the most powerful to affect Earth since March 1989, and produced aurorae at far more equatorial latitudes than usual in both the Northern and Southern Hemispheres.

The following report produced by Transpower provides a summary of the system operator and wider electricity industries response to, and lessons learnt from, the Gannon geomagnetic storm.

Southland Low Generation

Low hydro inflows in the Southland region had the potential, if the situation had worsened, to lead to security issues. This report outlines the potential issues and reconfiguration options.

Cyclone Gabrielle

Flooding during Cyclone Gabrielle caused extensive damage at our Redclyffe substation in Hawke’s Bay, resulting in the loss of electricity supply to Hawke’s Bay and Tairāwhiti.

Grid Emergency: Shortfall event

On 9 Aug 2021 the country faced the largest demand peak in response to one of the coldest nights of the year. As system operator, we called a Grid Emergency when insufficient generation was available to meet demand, leading to some customers being disconnected. A number of reviews of this event are underway including an independent review commissioned by Transpower to help us understand the event and industry’s response on the night, to identify where we need to make changes. As system operator, we have a programme of work underway to address recommendations from each of the reports, which includes industry engagement.

Reports and information relating to this event are located here.