Security of Supply and ERCs

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Latest Weekly Update Reported on 5 July 2022

(based on data at midnight 3 July)

Current Storage Positions

National hydro storage decreased by 1% to 89% of the historical average for the time of year. This remains within the historical 10th to 90th percentile range. High hydro generation in the first half of the week contributed to the decline in NI hydro storage despite average inflows. North Island hydro storage decreased by 18% to 147% of the historical average. South Island storage increased by 1% to 84% of the historical average for the time of year.

Market Indicators

Weekly Prices

Average prices decreased from the week prior. At Haywards, prices decreased by 7.5% from $182/MWh to $168/MWh. Prices generally stayed at around $200, with a few periods of $10/MWh-$20/MWh underpinned by high wind generation and low demand. Prices were high during peak demand periods on Tuesday and Wednesday where there was low wind generation.

Prices peaked at $726/MWh on Wednesday 29 June at 5:30 pm, where low wind generation and cold temperatures coincided with the evening peak. 

Weekly Demand

Continued cold weather helped sustain high demand at 849 GWh. Demand peaked at 6,764 MW on Wednesday 29 June at 5:30pm, as the evening peak coincided with cold temperatures and low wind generation. Demand peaks were relatively high in the first half of the week, and were tempered on Friday alongside increasing temperatures.

Generation Mix

Renewable contribution to the generation mix continued to decrease, dropping the percentage of renewable generation down to 82%. This is now lower than the renewable generation percentage at this time of year in 2019, but still higher than the previous two years. It included hydro generation, which decreased from 61% to 58% of the generation mix, and wind generation, which comprised 6% of the total generation mix. 

Thermal generation peaked mid week in response to high demand and low wind generation, similar to the week prior. Wind generation was low during Tuesday and Wednesday, then picked back up for the rest of the week.


Transfer across the HVDC link over the past week again reflected typical winter conditions, with high northward flow during the day and some periods of southward flow at night as a result of low demand. There continued to be some northward flow overnight due to low wind generation mid week.

Security of Supply Assessment (SOSA)

The 2022 Security of Supply Assessment was published on Thursday 30 June to the Transpower website.

Outages and Loss of Supply

No outages or loss of supply events to note. 

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 716.92 KB ]
Electricity Risk Curve Data [ xlsx 52.33 KB ] (Effective from 23 June 2022)
Simulated Storage Trajectories Files

Simulated Storage Trajectories [ pdf 248.04 KB ] (Effective from 23 June 2022)

Assumptions and Update Logs
Electricity Risk Curve and Simulated Storage Trajectories Assumptions [ xlsx 43.98 KB ] (Updated 23 June 2022)
Electricity Risk Curve Update Log [ pdf 6.53 MB ] (Updated 23 June 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 decreased in the North Island and increased in the South Island over the last week, with South Island storage at 61% of full and North Island storage at 67% 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 decreased and the South Island has increased.
  • Inflows over the last 4 weeks (Sunday to Sunday) in the North Island have been above average and in the South Island they have been above 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 82% of total generation, with hydro generation accounting for 64% 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

There are no security of supply consultations currently open.