Summary
Security of Supply
National hydro storage decreased by three percentage points this week to 129% of average for the time of year (77% of full). This was the result of very high hydro generation throughout the week, which comprised 67% of the generation mix.
North Island storage increased five percentage points to 119% of the historical average, and South Island storage decreased by four percentage points to 131% of the historical average.
Weekly Demand
National weekly demand was 744 GWh; a decrease of 44 GWh (six percent) on the previous week. This is likely a reflection of additional regions returning to Alert Level Three this week, combined with warmer weather across the country.
This week's national demand peak was 5,519 MW and occurred at 9.00am on Monday 4 October.
Generation Mix
Total generation was 780 GWh this week, with hydro making up 67%, and thermal just 7% of the mix. Wind generation comprised 4% of the mix, this represents a decline of three percentage points on last week.
The generation mix this week was 90.5% renewable.
Weekly Prices
The average price at Haywards was $67/MWh, down 17% from $80/MWh last week. This is likely due to abundant hydro storage across the motu.
Prices at Haywards peaked at $231/MWh at 4.00pm on Monday 4 October. This occurred during a period of inter-island price separation at a time when the HVDC was transferring 948 MW northward.
There were several sustained periods of inter-island price separation this week. This was due to the combined effect of high HVDC energy transfer North and HVDC filter outages at Benmore from the 4 October to 8 October. Filter outages impact the DC risk subtractor meaning that a DC contingent event (loss of a single pole) was setting the risk in the North Island, meaning that no reserves could be forward shared across the HVDC. Purchasing all the reserve in the North Island therefore led to high reserve costs and energy price separation.
HVDC
HVDC transfer has remained very strongly northward throughout the week.
Fact of the Week
When a wind turbine is non-operational they are shut down by ‘feathering the blades'. This means that the blades are allowed to twist in any direction the wind pushes them. This will protect the blades when the wind speed is too high or low to operate.
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