Summary
Security of Supply
National hydro storage dropped by four percentage points to 132% of average for the time of year (79% of full). This is despite continued above average inflows in both islands throughout the week and therefore is due to high hydro dispatch.
North Island storage increased three percentage points to 114% of average for the time of year. South Island storage decreased by five percentage points to 135% of average.
Weekly Demand
National weekly demand was 788 GWh; an increase of 30 GWh (four percent) on the previous week.
This week's national demand peak was 6,182 MW and occurred at 8.00am on Wednesday 29 September.
Generation Mix
Total generation was 823 GWh this week, with hydro making up 63%, and thermal just 8% of the mix. Wind generation comprised 7% of the mix.
There were two extended periods (totalling 10 hours) this week where thermal generation contributed 0 MW to the grid. However output from co-generation remained consistent.
Weekly Prices
The average price at Haywards was $80/MWh, up 170% from $47/MWh last week. This is likely the result of a slight decrease in wind generation and an increase in demand.
By comparison the average price at Invercargill was $20/MWh. An extended period of price separation was seen between Southland and the rest of the Motu (country) between 27 September and 1 October. This separation was the result of a planned outage on the Clyde-Twizel 2 line, which lead to constrained supply along remaining Naseby-Roxborough and Clyde-Twizel 1 lines.
As a result of daylight savings we saw lower consumption over the evening peaks this week. As such, this week's peak Haywards price, of $470/MWh, was recorded at 8.00am on Tuesday 28 September.
HVDC
HVDC transfer has remained Northward throughout the week.
Outages
On 28 September there was a grid emergency as a result of an unplanned outage on the BDE_EDN_1 line. This resulted in loss of power to the Edendale GXP.
On 30 September another unplanned outage at Kikiwa resulted in loss of approximately 30 MW of supply to Tasman and West Coast districts for two hours.
Fact of the Week
As the weather warms towards summer the System Operator reduces the amount of energy lines can carry. This is to reduce the amount of sagging in lines and maintain a safe distance between lines and the ground.
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