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Latest Weekly Update Reported on 17 May 2022

(based on data at midnight 15 May)

Current Storage Positions

National hydro storage has decreased by two percent to 77% of average for the time of year, dropping just below the 90th percentile of its historical range. This is a result of below average inflows in both islands and consistent hydro generation.

North Island storage has decreased by 11% to 81% of average for the time of year. Much of this decline is due to Lake Taupo dropping to about 30% of full, which is typical for this time of year as the lake often operates at the low end of its range. South Island Storage has decreased by 1.5% to 77% of average for the time of year. 

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 $224/MWh, a 7% increase from $209 MWh the week before. Prices peaked at Otahuhu at $807/MWh on Thursday 12 May at 8:00 am. This was driven by high demand, only 54MW of wind generation, requiring high levels of thermal generation over the morning peak. With some baseload thermal units not offering in the market, residual energy (generation offering in to the market not being used) reduced to 150MW.

There was minimal price separation throughout the week.

Weekly Demand

Demand increased slightly from the week before to 773 GWh. There were more distinct morning demand peaks in both Auckland and Wellington on Thursday and Friday as a result of the colder weather.

Demand peaked at 6,164 MW on Friday at 8:00am. This is the highest peak demand of the year to date signaling a shift in seasons.

Generation Mix

With demand increasing the generation mix has remained relatively constant with the growth being shared evenly between hydro and thermal generation. Hydro generation was 428 GWh, while thermal generation continued to make up a large part of the remaining generation mix at 141 GWh. Wind generation increased marginally from the week earlier to comprise 6% of the generation mix.


HVDC was again more northward, with only a few periods of southward flow. Northward flow was higher on days with low North Island wind generation.

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 630.44 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 decreased in the North Island and decreased in the South Island over the last week, with South Island storage at 62% of full and North Island storage at 31% 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 decreased.
  • 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 79% of total generation, with hydro generation accounting for 54% 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.