Transpower is responsible for ensuring there is enough generation to meet demand, while the Electricity Commission would put in place measures if the demand could not be met.
There are two options - shift the load away from peak demand or shed the load.
The first involves using controls, such as those on water heating, to reduce the peak demand at times of high use, such as in the mornings before work or early evenings.
That reduces electricity demand and, consequently, the generation.
The second is more drastic and involves switching off the electricity, which would be done by the 28 electricity lines companies.
That option would only apply when not enough electricity was available from generators.
Electricity Commission spokesman Peter Thornbury emphasised yesterday that rolling cuts were the last resort at the moment - and "very unlikely".
The commission was working with the electricity industry to finalise contingency plans around a whole range of issues associated with winter electricity use and one of those was rolling cuts.
The role of the commission was to issue a declaration of supply shortage, which would initiate demand management plans implemented by other organisations in the industry, including Transpower and electricity lines companies.
They were developing plans for that, including ensuring any cuts were shared equally.
Network Waitaki chief executive Graham Clark said measures to avoid a crisis were being driven by Transpower.
Electricity lines companies would do what they were told to do.
"At this stage, we have not been asked to do anything but urge people to use power wisely," he said.
Electricity lines companies could control electricity use through sending a signal to load control switches in houses which had them fitted.
Power savings are being posted twice a week - on Tuesdays and Fridays, on an Internet site created as part of the winter power savings campaign.
The www.powersavers.co.nz site has graphs showing hydro levels, in-flows into storage lakes, daily use and peak demand, along with a map showing power savings by region.
Transpower's chief executive, Patrick Strange, is convener of the Powersaver Group, which is running the winter power savings campaign on behalf of the electricity industry.
"While recent rain in South Island lakes was welcome, we do need more rain and prudent savings before we can say we are safely through the winter," he said.
Powersaver is asking business and residential customers to make some extra effort to reduce electricity use, particularly during peak demand between 7am and 9am and 5pm to 7pm.
So far, savings have been running at almost 2%, which do not include those made by large users such as the aluminium smelter at Tiwai.
Mr Strange believed large electricity users were contributing about the same level of savings.
The savings are calculated by comparing use with the same period a year ago, making adjustments for temperatures, demand growth and other factors.
New Zealand's major hydro storage lakes had been as low as 49% but were now 55% of average for this time of the year, and the electricity industry had started a nationwide power-savings campaign.
During the past week, Lake Pukaki was at 522.4m above sea level (minimum operating range 518.2), Lake Tekapo 705.8 (702.1), Lake Ohau 519.78 (519.75), Lake Manapouri 177 (176.8) and Lake Te Anau 202 (201.5).
After generating through its Waitaki hydro system earlier this month because the Manapouri system was close to minimum, Meridian Energy has switched back to Manapouri after good in-flows boosted storage lake levels.
That is reflected in the flow of the Waitaki River, which has been running at around 160 to 180cumecs last week compared with 300 to 400cumecs late last month and at the beginning of June, when it was substituting for Manapouri.
Energy savers
You can save electricity by. -
• Switching off appliances at the wall.
• Putting the heated towel rail on a timer, or switching it on when needed.
• Checking your hot-water cylinder - it should be at 55degC.
• Drying laundry outside where possible.
• Use sunlight to warm your home, then close blinds or curtains to retain heat.
• Use the right-sized saucepan to match the heating element and a lid to keep the heat in.
• Fix drips in hot-water taps.
• Install an efficient, low-flow showerhead.
• Stop draughts.
• Use a log or pellet burner for heating.
• Fit energy-efficient bulbs.
• Switch lights and heaters off in rooms not being used.
• Reduce condensation in house by opening curtains, windows and doors during the day.
