Transpower confident there won't be power cuts tonight

Genesis Energy's coal and gas fired plant at Huntly. Photo / File

Transpower is confident enough electricity is being generated to ensure the system operates as it should this evening and over the long weekend.

This morning, the electricity system operator declared a "grid emergency" when there was an unexpected loss of electricity generation.

Contact Energy's 105 megawatt peaker at Stratford failed to start, one of Genesis Energy's units at Huntly had to temporarily reduce output by 150 megawatts, and wind generation dropped from a forecast 90 megawatts to 30 megawatts.

Transpower worked with lines companies to remove some demand from the electricity system. Lines companies briefly switched off electricity used by some hot water cylinders – a move Transpower said is made regularly during winter, which doesn't impact people.

Transpower spokesperson Nathan Green told the Herald there is expected to be 440 megawatts of residual electricity generation available this evening – a buffer sufficient to ensure supply meets demand.

Furthermore, he said temperatures are forecast to rise a little and demand for electricity is likely to fall over the long weekend.

Transpower chief executive Alison Andrew assured that lines companies knew what was expected of them this morning, and "they moved quickly to manage controllable load and reduce demand to get us through the emergency".

"No one was disconnected, and the system stayed stable throughout," Andrew said.

Contact Energy chief generation officer John Clark said a mechanical fault meant the company's fast-start gas peaker couldn't be switched on. The cause of the fault is still being investigated.

Clark said all of Contact Energy's available generation was supplying the electricity grid on Thursday morning.

He said Transpower did its job, asking for extra supply and reduced demand.

"The system responded with additional electricity made available by generators, and demand from electricity consumers reducing," Clark said.

Genesis Energy said an electrical fault on a fan reduced output from one of its units at Huntly from 240 megawatts to 108 megawatts.

"Unit 4 is back up and running and available to 220 megawatts and we anticipate the unit to be fully available for the evening peak," Genesis said.

Addressing Parliament's economic development, science and innovation committee on Thursday morning, Energy and Resources Minister Megan Woods said "ripple control" – cutting power to hot water cylinders for a short time – was deployed "a whole lot more" on Thursday morning than in August last year, when a lack of generation caused widespread power outages.

Woods said Thursday morning's situation showed coal and gas aren't as "fail-safe" as some people assume.

"What this actually shows me is that there are fragilities in the system, and most of those fragilities have actually been because of the failure of our fossil assets to spring into action to provide that stability to the grid that we need," she said.

However Clark, of Contact Energy, said the situation demonstrated "the importance of New Zealand having a diverse portfolio of generation assets to cover intermittent generation like wind".

The Electricity Authority, in April, completed its final review of the August 9, 2021 power cuts that left 34,000 customers without electricity on one of the coldest nights of the year.

The review confirmed Transpower's co-ordination and communication failures meant consumers were disconnected unnecessarily.

Jarden director of equity research, Grant Swanepoel, said Transpower obviously doesn't want a repeat of this situation.

"We do have a fairly tight market going into this winter with hydro levels being still lowish, so we need a bit more water," Swanepoel said.

"It's a pretty tight market but wholesale prices are not reacting."