Residents plunged into darkness last night when power generators were deliberately shut to manage record electricity demand have expressed anger and surprise at the decision.
Transpower says New Zealand hit a peak electricity demand of 7100MW between 6pm and 6.30pm last night Photo: RNZ / Diego Opatowski
Important power generation back-ups were not up-and-running, despite plenty of warning a cold snap was on its way.
The Energy Minister has called out the power companies, saying the rolling blackouts were preventable.
The power went out without warning, leaving thousands with no time to fill their hot water bottles or find torches.
Napier resident Jean McDonald was just about to cook dinner when her power went out, and said she would have appreciated prior notice.
"I was angry I thought in this day and age of modern technology they could've sent a text out, if it was something they wanted they would do that, just to let you know and I could have had a few things put in line and been prepared for it," she said.
"It's the lack of information and the fact that today we shouldn't have power cuts it took me back to my childhood in the 1950s when we had power cuts."
When the power went out at her house, Stokes Valley resident Helen Pentecost drove to be with her 99-year-old father who lived nearby.
"It did come as a bit of a surprise to me that we were that short of power in the country that we had to do this."
MBIE data shows the country's total capacity to generate power is more than 9000MW - below the peak of 7100MW that Transpower said New Zealand hit between 6pm and 6.30pm last night.
Meanwhile, wholesale electricity spot prices soared yesterday, reaching an average of $7000 per megawatt hour - up from the usual $100.
A consumer advocate for electricity, Molly Melhuish, said that price spike would eventually filter through to household bills.
"I think it will result in big profits and people always see the result of excess profits on their bills sooner or later," she said.
Consumer New Zealand runs Powerswitch, a platform for comparing power prices and switching providers.
Its manager, Paul Fuge, said the rolling power cuts offer further evidence the market favours companies, not consumers.
"It's a big concern for us and it's something we keep an eye on. We've got concerns with the market in general, how the electricity market is performing for consumers and we don't believe it is delivering the optimal results for households."
Genesis said Transpower did not ask it for more electricity until just after 5pm last night on the cusp of the evening peak demand.
The company said it did increase supply at its Tokaanu site but gale force winds earlier in the day had pushed weed into the intake at the plant, which ultimately tripped losing 115 megawatts of generation.
It said elsewhere it was operating at full capacity.
Transpower has assured customers that power won't be intentionally cut again tonight.
Its general manager of grid development, John Clarke, says extra generation has been made available, after thousands of New Zealanders were left in the dark last night.
Meanwhile, The Energy Minister Megan Woods has blamed the power cuts on commercial decisions made by the electricity companies.
She has blamed Genesis Energy, in particular, for failing to turn on its third generator at Huntly, despite having been warned there would be massive demand.
Genesis CEO Marc England rejected claims commercial decisions had prevented supply being met. He told Checkpoint a build-up of weeds in a hydro lake and a lack of wind for turbines had hampered supply.