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

July 2025 Energy Security Outlook

Energy Security Outlook - July 2025.pdf (PDF 3.57 MB)
The national controlled hydro storage position has slightly improved since last month's update and now sits at 98% of the historic mean as of 24 July.
The Electricity Risk Curves (ERCs) for August 2025 and throughout 2026 have dropped relative to the June update. This is due to an increase to coal stockpile forecasts, gas storage and forecast gas production.
No Simulated Storage Trajectories (SSTs) cross the Watch curve in 2025. Five of the 93 SSTs cross the Watch curve in January-July 2026. This assumes the third Rankine unit retires in January 2026 and the market supplements the existing coal stockpile at its maximum import capability to maintain increased thermal generation during low hydro inflows.
The market response ahead of winter 2025 to reduce hydro storage risk has been effective in limiting the impact of ongoing below mean storage levels in the South Island. Looking ahead to winter 2026, the risk to electricity supply can be decreased through hydro storage management and ensuring there is sufficient backup thermal fuel and capacity to support increased thermal generation under extended periods of low inflows.
In this month's scenario we look at the impact on the ERCs if the third Rankine unit were to remain available. This lowers the ERC Watch curve by up to 623 GWh and results in no SSTs crossing the ERCs.

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