Security of Supply and ERCs

Quick Links


Latest Weekly Update Reported on 24 May 2022

(based on data at midnight 22 May)

Current Storage Positions

National hydro storage has increased by two percent to 79% of average for this time of year, remaining just below the 90th percentile of its historical range. This is due to an inflow event, which was more impactful for both the Manapouri and Te Anau catchments.

North Island storage has increased by 5% to 86% of average for this time of year. South Island storage has increased by 1.9% to 79% of average for this time of year.

Aligned with the start of the Maui outage we have observed Methanex curtailing their demand, which is releasing gas to other industries.

Market Indicators

Weekly Prices

Prices continued to hover around the $200 mark, reflecting the below average hydrology, and upward price pressure on thermal fuels including carbon.

The average price at Haywards was $199/MWh, an 11% decrease from $224 MWh the week before. Prices fell drastically to $5/MWh in the early hours of Friday the 20th as a result of 659 MW of wind generation during the overnight demand trough.

Weekly Demand

Demand decreased slightly from the week before to 766 GWh. The national demand profiles remained relatively consistent from Monday to Friday with an anticipated drop for the weekend. 

Demand peaked at 6,047 MW on Friday at 6:00pm. This is a two percent decrease from the previous week's peak of 6,164 MW.

Despite the slight decline in demand from the previous week, we experienced the first winter storm for the year, which led to four relatively small loss of supply events on Friday the 20th.

Generation Mix

National generation was 797 GWh this week. In reflection of current hydrology, hydro generation comprised 51.6% of the total generation mix (a 2% reduction on the week prior). Despite TCC having returned to the market since Tuesday the 17th, thermal generation comprised 16.4% of the generation mix (a 1% reduction on the week prior). Wind generation increased significantly from the week earlier to comprise 10% of the generation mix. Wind generation peaked at 728 MW on Thursday the 19th at 5:30pm.


This week we saw daily periods of southward HVDC flow through the night due to a combination of high wind, low demand periods and higher North Island baseload thermal generation. The highest northward flow was 570.

2022 Security of Supply Annual Assessment Consultation

The draft 2022 Security of Supply Annual Assessment (2022 SOSA) is currently out for consultation available here on the Transpower website. Consultation on the 2022 SOSA closes at 5pm on 08 June.

2022 Ancillary Services Procurement Plan

The new 2022 Ancillary Services Procurement Plan (effective 03 May 2022) is now live on the Electricity Authority website here. The new procurement plan enables BESS to provide injectable reserves in the instantaneous reserves market. 

Electricity Risk Curves

New Zealand and South Island storage are both in the Normal range.

Electricity Risk Curves

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

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

Click here to learn more about the Electricity Risk Curves and thermal fuels validation

Electricity Risk Curve Files
Latest New Zealand Electricity Risk and South Island Electricity Risk Curves [ pdf 630.7 KB ]
Electricity Risk Curve Data [ xlsx 50.92 KB ] (Effective from 21 April 2022)
Simulated Storage Trajectories Files

Simulated Storage Trajectories [ pdf 271.06 KB ] (Effective from 21 April 2022)

Assumptions and Update Logs
Electricity Risk Curve and Simulated Storage Trajectories Assumptions [ xlsx 44.36 KB ] (Updated 21 April 2022)
Electricity Risk Curve Update Log [ pdf 5.61 MB ] (Updated 21 April 2022)

Electricity Risk Curve and Simulated Storage Trajectories Assumptions [ pdf 357.49 KB ] (base document effective from 21 May 2021)


No Gas Swap Scenario [ pdf 1.22 MB ]  (Updated March 2022)

Simulated Storage Trajectories - No Gas Swap Scenario [ pdf 279.21 KB ] (Updated March 2022)


No Third Rankine Scenario - January 2022 [ pdf 1.06 MB ]

Simulated Storage Trajectories - No Third Rankine Scenario - January 2022 [ pdf 765.96 KB ]

Hydro Information

For security of supply purposes, hydro storage is divided into two categories; controlled and contingent storage. Generators can use controlled storage at any time, but contingent storage may only be used during defined periods of shortage or risk of shortage. During sustained dry periods, controlled and contingent storage are important indicators of overall supply risks. Storage is expressed in gigawatt-hours – GWh (a measure of the energy that can be produced using the water).

Storage increased in the North Island and increased in the South Island over the last week, with South Island storage at 63% of full and North Island storage at 33% of full.

Lake Levels

Island Inflows and Storage

The charts below show storage over the last 13 weeks and rolling 7 day inflows for the last year in North and South Islands. 

  • Over the last week (Sunday to Sunday) available storage in the North Island has increased and the South Island has increased.
  • Inflows over the last 4 weeks (Sunday to Sunday) in the North Island have been below average and in the South Island they have been below average.
North Island South Island
Contingent Storage

Contingent storage is stored hydro that is only made available for generation at specific times to mitigate the risk of shortage. Current available contingent storage is shown on the following graph.

For more information on contingent storage and the conditions of its use, refer to the documents below.

Contingent Storage additional information [ pdf 167.95 KB ]
SOS101 - Contingent Storage [ pdf 175.52 KB ]

Market Indicators

Demand, generation mix, HVDC transfer and prices can all indicate the market response to the current security of supply climate.

Renewable generation over the last seven days was 81% of total generation, with hydro generation accounting for 52% of total generation.

Weekly Generation


Electricity consumers range from large industrial sites (the most significant is the NZAS aluminium smelter at Tiwai), down to individual households. Almost two thirds of national demand is located in the North Island. New Zealand's annual electricity consumption ('demand') is nearly 40,000 gigawatt-hours (GWh). If demand differs from expected, it may impact on security of supply.


Hydroelectric generation contributes around 60% of New Zealand's total electricity supply, with many generators of widely varying sizes distributed throughout the country.

HVDC Transfer

The ability to transfer electricity from one island to the other is an important aspect of managing security of supply, particularly as there are no thermal stations in the South Island to call upon in times of low hydro storage. Net weekly HVDC transfer is shown in the chart below with north transfer from Benmore to Haywards and south transfer in the opposite direction.

Wholesale Spot Prices

Spot prices can be an indicator of security of supply risk. Typically they rise when supply is tight, such as during 'dry years'. Weekly 7 day rolling spot prices for each island are shown in the graphs below. The corresponding prices for the previous year are also included for comparison.

Industry Workshops

We run security of supply workshops on topics of interest to the industry. The 2021 Workshops on Security of Supply are linked below.

3 Jun 21 18 May 21 3 May 21 20 Apr 21 7 April 2021 31 Mar 21 26 Feb 21

Policies, Plans and Publications

Includes information on the Annual Assessment and Transpower policies related to Security of Supply: the SoSFIP, EMP, SOROP and Outage watch List

Security of Supply Consultations

We are currently seeking comments on the  Security of Supply Assessment 2022, submissions close 5pm on the 8 June 2022.