Lines company Aurora Energy has not found a cause for the power outage on January 19 which affected nearly 8000 customers from Clyde to Beaumont and St Bathans.
On Friday power went out again for customers in parts of Alexandra and as far as Lauder for up to 10 hours at some properties.
Transpower, the government-owned agency that connects electricity generators to major electricity users and distribution networks such as Aurora, has warned of rolling electricity outages during the coming winter.
Their Winter Outlook has highlighted the risks if winter is severe because of pressures on ensuring sufficient generation, maintaining the lines network and managing increasing demand.
Chief executive Alison Andrew told RNZ’s Nine to Noon New Zealand was reliant on established resources but hydro lakes were only at average levels and two large power generators — a wind farm and a geothermal station — had commissioning problems.
"There just isn’t enough capacity in the system and we can also face a dry winter.
We don’t have enough water which [we] rely on very heavily in our system, and if that’s the case we could get into rolling power cuts."
The system would need coal and gas burning thermal stations to provide backup, but they took time to fire up and would result in higher prices.
The country needed more flexible power generation, such as gas-fired peakers, which could be turned on at short notice to provide greater security, she said.
In October, New Zealand solar developer Helios unveiled plans for a 660ha solar farm on farmland between Naseby and Ranfurly capable of powering 70,000 homes.
This week Helios spokesman Jonathan Hill said they were actively developing the Naseby-Ranfurly resource consent application for the 300-megawatt project on land owned by two local farming families.
At drop-in sessions in Ranfurly last year the company pointed out solar farms were relatively quick to install and have up and running.
Work on a pumped hydro project at Lake Onslow, above Roxburgh, was halted following last year’s election.
It was estimated to cost nearly $16billion and take nearly 10 years to be commissioned.
Axing the project in December, Energy Minister Simeon Brown said the Government was committed to cutting red tape to drive investment in renewable electricity generation.
"Demand is forecast to increase by two-thirds by 2050 and we need to build enough generating capacity to meet that demand.
To do this, we’re going to need to significantly increase the amount of clean energy we generate from solar, wind and geothermal."
Age Concern volunteer and former co-ordinator Marie Roxburgh said long winter power cuts had significant effects on older people, but they were unlikely to complain.
"We know our work will double making sure everyone was OK."
A full-day power outage last year was "devastating", Mrs Roxburgh said.
"It can be an eternity for old people. How do they fill in the day?"
Emergency management adviser for Central Otago and Upper Clutha Jacqui Lambeth said Aurora had committed to supplying generators to communities during long outages so people could make a hot drink and charge their phones.
There were some community response groups who had small generators at the local hall which could be opened during a power cut.
While she was one of those without power for 10 hours on Friday, a small gas cooker and stored bottles of water meant it was bearable, she said.
However, a summer power cut was "entirely different" to a winter one, Miss Lambeth said.
Central Otago Mayor Tim Cadogan said initially he was concerned about the lack of clarity on outages with no reason but had since been given information suggesting Aurora’s outage numbers were in line with other suppliers, which gave him comfort.
Aurora Energy’s general manager for network operations, Matt Settle, said at the time of the outage on January 19, one of the two lines that feed the Central Otago network from the Clyde grid exit point (where Aurora Energy takes electricity from Transpower’s national grid) was out of service to enable Transpower to undertake essential maintenance on their grid assets.
The remaining single line was designed to cope with being the sole supply.
A fault on the working line cut supply to all customers. If both lines were operating the fault would not have been noticed, Mr Settle said.
"There were no visible faults with the line itself and at this stage we suspect an outside interference such as a tree or animal contact."
It was not unusual for lines companies to be unable to pinpoint the cause of every fault because some fault conditions occur only momentarily, making them difficult to detect.
That could be from vegetation, animals or birds making contact with the lines, he said.
On Friday the outage was on the line that had been out of service on January 19. Both lines were in service at the time.
The primary protection system did not operate as planned, causing a trip to both lines and loss of supply to all customers.
There was no safety risk, but the protection didn’t manage the fault and load transfer as intended.
The protection settings had been corrected and tested, Mr Settle said.
A specialist acoustic inspection was planned later this month to check for faults and animal protection mitigations, such as possum guards, were being reviewed.
