Transpower modelling shows heightened risk of power shortages on July 26

Wednesday, 25 May 2022

There is a heightened risk of power shortages this winter as a result of maintenance work on Contact Energy’s Taranaki Combined Cycle gas power station, modelling by grid operator Transpower shows.

Transpower’s forecasts have identified a rare “N-1” shortage on July 26, which means that electricity generation could fall short of demand if just one very major unexpected event happened that day.

An unplanned outage of the largest of the Huntly Power Station’s five turbines could be enough tip the electricity market into deficit that day based on Transpower’s current models, the grid operator confirmed.

Transpower also advised power companies on Monday that its forecasts showed there were now 37 days between June and August when there could be a “N-1-G” shortfall, based on its current modelling.

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That means there would be a risk of power shortages if two big problems struck at once.

A Transpower spokesperson it had been at least five years since its modelling had last detected a potential N-1 shortfall.

But the state-owned enterprise is playing down the risk of power cuts actually materialising, saying the forewarning it is providing the power industry should mean the industry can prevent that.

Transpower operations manager Stephen Jay said its model was “a conservative tool in which we use the highest historical demand peaks in recent years to identify where there could be a potential shortfall”.

Transpower operations manager Stephen Jay says the tool Transpower users to monitor the risk of power shortages is “conservative”.

The notices it had issued to power companies “generally prompts action from the industry that is sufficient to relieve these kinds of situations”, he said.

That could include delaying maintenance or increasing the size of their power offers to the market.

“It is often the case that as we get closer to the date, weather forecasts show that peak demand will be less than the level we used for the initial … assessment,” Jay said.

The 377 megawatt Taranaki Combined Cycle gas power station, which was built in 1996, often plays a key role in helping generators meet periods of peak electricity demand.

Contact Energy spokesperson Leah Chamberlin-Gunn said it could only be run for another 2000 hours before further maintenance and an outage was required.

“The timing for this additional maintenance is subject to contractor availability. Ideally we’d avoid the middle of winter but we are reliant on access to the contractors,” she said.

“We’ve managed to reduce the outage period from five weeks to three weeks, with the work indicatively scheduled for late July through to early August.”

Transpower had not been modelling a risk of power shortages on August 9 last year, when it triggered power to be cut to 34,000 homes because of a crisis that emerged more suddenly.

The triggers for that shortage included a passing polar storm that sent temperatures plunging, a lull in the wind, and an unplanned outage of Genesis Energy’s Tokaanu hydro power station which was caused by the storm stirring up weeds and blocking a water intake.

The Electricity Authority found Transpower had also been unclear about actions it wanted power companies to take early on the day to boost generation.

Mercury Energy general manager of sustainability Lucie Drummond said it was positive that Transpower was notifying power companies of concerns about peak winter demand now.

“That, if anything, signals a better level of communication,” she said.

“Everybody’s minds are very focused on not having outcomes like we had on August 9. I am not aware of any major concerns that are coming from the sector itself,” she said.

John Harbord, chair of the Major Electricity Users Group, said Transpower had “really developed its forecasting abilities” and it was helpful for potential issues to be flagged far in advance.

But potential generation shortfalls also highlighted concerns about the amount of generating capacity in the market, he said.

“Generators have signalled their intention to build additional generation but some of that has not been confirmed yet and there is obviously a lag time between that and producing electricity.”

Correction: An earlier version of this story stated that Lucie Drummond’s job title was chief executive of Mercury, rather than its general manager of sustainability. (Amended May 25, 2022, 4.45pm).