Threat of power cuts as temperatures drop below -6C

Parts of the country are waking to below freezing temperatures, amid fears there won't be enough electricity to go around this morning.

Transpower has warned the crunch time for demand will be between 7am and 9am and there could be power cuts if demand is too high.

'The situation is still really tight'

Transpower's executive general manager, Chantelle Bramley, says power supply is tight this morning and there is the potential for a shortfall of electricity during peak times.

The national power grid operator is asking New Zealanders to carefully manage their electricity usage between 7am and 9am.

Bramley told Morning Report it was slightly colder in the North Island than originally forecast, so the demand for electricity could even be higher than initially expected.

She said Transpower was doing its best to avoid enforcing controllable load measures, which would include managing the power to things like hot water heaters.

"The situation is still really tight this morning. We've got very cold weather across the country, it's actually slightly colder in the North Island than originally forecast so that means that we could expect load to be even higher."

While there was a bit of a wind around which was helping to generate some power, "at this point there is still the potential for a shortfall going into this morning's peak between 7am and 9am".

Industrial users were also doing their bit, she said, and power generators had responded well.

People were not being asked to turn off their heating, just to dial it back one or two degrees, and turn off any extra lights.

She was not aware of any outages so far.

May could be a challenging time for power supply as generators tried to get maintenance done before the winter peak.

More than 700 megawatts of supply were out of action at present, Bramley said.

"It would always be good to have more flexible generation in the system to meet these sorts of mornings."

The generators were responding to Transpower's request for this, she said.

'Unusually cold start to May'

The coldest place is Christchurch on -6 degrees, MetService said.

It's -2 in Masterton, Blenheim and Wanaka and zero degrees in Hamilton.

The warmest places are Invercargill and Dunedin on a balmy 10 degrees.

MetService meteorologist John Law spoke to Morning Report from the Wellington waterfront.

"It's an unusually cold start to May, looking at some places like Christchurch, for example, down to minus 6.3 Celsius last night. That's unsually cold for any night in May...that air coming up from the south.

"Then of course there's these nice clear skies we've had in the last few nights allowing any of that daytime heat to dissipate once the sun sets."

Part of the pressure on the country's power supply is due to the lack of wind for the wind farms.

Law said this was due to a big area of high pressure across the country so there were very as a very light winds across most of the country.

While the conditions could be attributed to a southerly polar blast, there would be no storms with a high pressure system keeping conditions clear.

He forecast more chilly nights to come through the weekend while next week would be warmer and wetter.

However, it would not be a boon for the country's skifields with no snow expected as part of the cold snap.

The sun is due to be shining in most places this morning, with a few showers scattered across the east coast.

Appeals to conserve electricity will become more common

Meanwhile, a group representing big industry is warning that appeals to conserve electricity will become more common.

The Major Electricity Users' Group, which represents big industry, is warning that appeals to conserve electricity will become more common.

Its chair, John Harbord, says that is because of the country's growing reliance on renewable energy.

He says when the wind's not blowing and it is dark so there's no sun for solar, these types of scenarios become more likely.

What you need to know:

Transpower has warned households that unless they conserve electricity, they could face possible power cuts on Friday.

It said households could help by turning off heaters and lights in unused rooms, delaying using appliances, and not charging devices and cars.
The time of main concern for power shortages was between 7am and 9am on Friday morning.
New Zealand's largest electricity distributor is warning the country to hurry up with controls around charging electric vehicles or face unnecessary bills running into the billions.
A group representing big industry is warning that appeals to conserve electricity will become more common.

Main image (Photo: RNZ/Rebekah Parsons-King): Transpower is trying to avoid electricity cuts this morning.