Energy Security Outlook

The Energy Security Outlook (ESO) is a monthly report that helps track how secure New Zealand’s electricity supply might be over the next two years. It uses two key tools, the Electricity Risk Curves (ERCs) and Simulated Storage Trajectories (SSTs), to show how likely it is that we’ll have enough electricity, especially during dry periods when hydro lakes are low.

For more information on how it works and why it matters, we have published an 'ESO 101' document that covers how ERCs and SSTs help forecast electricity risks, what triggers action when supply looks tight, and how extra hydro storage can be used if needed.

Energy Security Outlook 101

October 2025 Energy Security Outlook

Energy Security Outlook - October 2025.pdf (PDF 3.48 MB)

The national controlled hydro storage position has increased since last month's update and sits at 143% of the historic mean at 28 October (up from 102% at 25 September). South Island storage is at 142%.
This month's base case models the third Rankine remaining rather than it retiring in January 2026. This change reflects the Commerce Commission's draft determination to authorise the agreements between the gentailers to keep the third Rankine up to the end of 2035.
In this month's scenario we look at the impact if the third Rankine were to be retired in January 2026. This raises the NZ Watch curve by up to 713 GWh, and given the hydro storage as of 15 October there are three SSTs crossing the Watch curve in 2026 in May and June.
The Electricity Risk Curves (ERCs) for 2026 have reduced primarily due to the base case now assuming the retention of the third Rankine. There has been a small additional decrease in the early months of 2026 due to an increased starting coal stockpile and an improved gas production forecast. The risk curves for the remainder of 2025 are materially unchanged and mostly set by the Alert and Emergency floors reflecting energy held in contingent hydro storage.
No Simulated Storage Trajectories (SSTs) cross the Watch curve in 2025 or 2026. This assumes the market supplements the existing coal stockpile at its maximum import capability to maintain increased thermal generation during low hydro inflows.
Looking ahead to winter 2026, electricity supply risks can be reduced through hydro storage management and ensuring sufficient backup thermal fuel and capacity to support increased thermal generation under extended periods of low inflows.

The graphs below compare New Zealand and South Island controlled storage to the relevant Electricity Risk Status Curves.