Security of Supply

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Daily reporting

We are required to report daily on key market indicators once national hydro storage levels are at the 1% Electricity Risk Curve (ERC). Given our current adjacency to the 1% ERC, we, as System Operator, have initiated daily reporting. We will use our judgement with regard to how long this will be necessary and to avoid cycling in and out of daily reporting when storage levels are otherwise close to the 1% ERC.

The daily update will be produced on Mondays, Tuesdays, Wednesdays and Fridays and  contain summary text on key changes to security of supply with a full suite of charts. On Thursdays we will produce the normal weekly report with hydrology information up to midnight Tuesday.

Latest Weekly Update Reported on 6 May 2021

(based on data at midnight 4 May)

Current Storage Positions

As a result of low inflows across the country this week both North and South Island hydro storage has declined. North Island storage decreased by 13 percentage points to 33% of average for the time of year. South Island storage decreased by two percentage points to 67% of average. Overall national hydro storage has dropped two percentage points to 65% of average for the time of year, this is 50% of total full. 

There are moderate rain events expected in catchment areas in the next five days; therefore we expect to see further sideways movement in hydro storage levels.

Our current hydro position is 363 GWh above the 1% ERC (1,860 GWh).

Market Indicators

Thermal Fuels

Huntly 5 has now returned to service. 

There are a number of planned gas production outages in early May. You can find more detail on these here

Genesis have released a statement regarding securing additional short term gas supply. More information on this can be found here

Nova has requested that we include the following information in this edition of our newsletter:

With the arrival of winter temperatures, Todd Generation Taranaki Limited advises that:

  • from time to time atmospheric conditions affect Junction Road Peaker's ability to generate due to plant risk
  • this occurs where humid conditions combine with low temperatures, and is only expected to have impact for relatively short periods of time (2-8 hours), in particular overnight

Fixes to this issue will be installed with the May outages outlined on POCP. This issue will be fully resolved by June.

In the meantime TGTL will only be offering Junction Road to the market where it is confident the plant can run. From time to time this may mean Junction Road is offered to the market at short notice.


National demand increased to 775 GWh this week as business resumed following the ANZAC day public holiday and temperatures dropped.


Prices increased on last week, averaging at around $283/MWh at Haywards.

Generation Mix

Of last weeks generation mix, wind comprised 4% and hydro 50%. Overall, renewables made up 73% of total generation.

HVDC transfer

The trend of relatively low northward transfer and increased southward transfer continues due to dry conditions.

Electricity Risk Curves

Further information here.

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


Hydro Information

Further information here.

Storage decreased in the North Island and increased in the South Island over the last week, with South Island storage at 55% of full and North Island storage at 13% of full.

Market Indicators

Further information here.

Renewable generation over the last seven days was 73% of total generation, with hydro generation accounting for 50% of total generation.

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 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


There are currently no consultations on security of supply.