New Zealand has been told its electricity supply for the coming winter should be safe.
The sureity is in part being credited to a decision last year to reprieve two coal and gas burning power units at Huntly.
New Zealand endured repeated power crises in the first decade of this century as dry weather deprived hydro storage lakes of water and cold winters meant people used more electricity for heating.
There have been no repeats this decade, despite some dry weather. This year also looked likely to be safe.
The forecast came from Transpower, which, as well as running the national grid, must ensure the technicalities of the electricity system work.
Transpower relied on Electricity Authority formulae in making its prediction for winter.
The formulae state how much spare generating capacity should be available, ensuring there is enough for safety, but not so much that power plants sat idle, incurring costs that would be passed on to the consumer.
In its statement, Transpower said the electricity system would meet the criteria this year.
At this stage, the safety assurance lasted for one year.
A modest increase in electricity production would be needed in 2018 and significant investment from 2022 onwards.
Transpower said these predictions were based on the assumption the Tiwai Pt Aluminium Smelter remained in business.
It uses about one seventh of New Zealand's electricity. It had the right to shut down from next year onwards, but had made no moves to indicate this was likely.
Transpower said its scenarios would change if the smelter closed, because this would free up unused energy for the general market, reducing the need for a new generating plant.