The near-miss grid emergency on Friday morning shows the need for more back-up for the national grid, an energy analyst warns.
National grid operator Transpower asked households and businesses to conserve electricity due to a cold snap, coupled with several power plants undergoing maintenance.
The country got through the power supply threat by a narrow margin, Transpower said.
A combination of consumer and business conservation measures and full use of available electricity generation gave it a margin of safety.
Energy sector research firm Enerlytica research head John Kidd said the response was commendable but warned of a tight winter.
"The margins were tight this morning, there's no denying that. But the industry did respond, demand did come off on request, and there was some additional supply that did come in," Kidd told Midday Report.
"But it is indicative of what is going to be a tight winter.
"We're short on capacity compared to what we do need."
It was a confluence of issues - low winds and plant outages, combined with high demand, he said.
He was "sure" the country would face a similar situation again in winter.
Huntly's coal-powered plants were holding power supply steady at the moment, he said.
"We already have as much as what we're going to get in the system out of coal."
But the country needed to invest in more rapid-fire options to cope with demand surges, Kidd said.
Solar power company SolarZero said in response to the potential energy shortage, the company provided 30 megawatts of electricity from its nationwide network of batteries, the equivalent of 100,000 hot water systems.
It said 5 megawatts came from the South Island, equivalent to the surplus energy available today.
SolarZero said its battery network, called a virtual power plant, could operate like a grid-scale battery and work faster than coal and gas.
Advocacy group for elderly people Age Concern said the squeeze on power was a timely reminder to prepare for blackouts.
It was important to have a plan in case power was lost due to storms or other disasters, Age Concern chief executive Karen Billings-Jensen said.
However, people should be reassured that wholesale cuts were unlikely, and they should not sacrifice their health to save power, she said.
In a statement, Transpower chief executive Alison Andrew said the response was now over and there was no reason to expect any further need to conserve electricity today or this weekend.
