Security of Supply
A week of above average inflows in both the North and South Island saw the national hydro storage increase by 8% to 88% of the historical average for the time of year. This is now within the historical 10th to 90th percentile range. North Island storage increased by 28% on the previous week to 140% of the historical average and South Island storage increased by 7% to 84% of the historical average for the time of year.
The Maui full field outage has been further extended and is now expected to finish on Sunday 19 June. Methanex continues to reduce consumption, helping to balance the gas supply.
Demand slightly increased from the week prior to 779 GWh. Cooler temperatures in the South Island contributed to the increase in demand and counteracted the lower demand normally seen during a week with a public holiday. Demand peaked at 6,224 MW on Thursday 9 June at 6:00pm, during a period of low temperatures in the South Island. Demand peaks were tempered as the North Island experienced milder temperatures despite extreme wind and rain.
86% of the generation mix was renewable generation. This is the highest percentage of renewable generation seen for this time of year over the past four years. This included hydro generation, which made up 57% of the total generation mix, and wind generation, which increased from the week prior to comprise 10% of the generation mix.
Thermal generation peaked early in the week and remained relatively high throughout the week. However there were periods without Huntly U5 and rankine units running due to low overnight demand, high output from run-of-river North Island hydro schemes and high North Island wind generation.
The average price at Haywards was $146/MWh, a decrease of 15% from $172 MWh the week before. Prices hovered around $200/MWh during the start of the week, with greater price fluctuations for the second half of the week including several periods of near $0/MWh prices. The fluctuations coincided with strong wind generation, low thermal generation and low overnight demand.
Prices peaked at $249/MWh on Monday 6 June at 17:30pm during a period of low wind generation coinciding with the evening demand peak.
Transfer across the HVDC link over the past week again reflected typical winter conditions, with northward flow during the day and some periods of southward flow at night as a result of low demand, higher North Island baseload thermal generation, and high winds.
Outages and Loss of Supply
There were several outages on the low voltage networks with 100,000 lightning strikes seen across the country. Only one momentary loss of supply resulted. This was in Wellington on Thursday 9 June 12:22pm.