Transpower ‘closely monitoring’ risk of electricity shortfalls in September

Thursday, 10 August 2023

Still burning coal, Genesis Energy are thinking hard about how their electric edifice on the Waikato River can be made fit for the future.

Transpower has acknowledged there is an increased risk of power cuts ahead after the largest of the five turbines at Genesis’ Huntly power station broke down at the end of June.

Operations manager Stephen Jay said it was closely monitoring the risk of shortfalls in generation in September that could transpire in a scenario that it plans for where two additional things went wrong.

However, it appears to be a case of “so far, so good” this winter, with relatively few occasions when Transpower has had to call on generators to increase their generation in response to tight supply.

Concerns have been growing over the past few years that thermal power plant outages could become common as the country moves closer to phasing out coal and gas generation and investment in it becomes harder to justify.

Unit 5 at the Huntly power station failed at the end of June and Genesis announced last week that it might not be fixed until the end of May.

Jay said the gas turbine had an output of about 380 megawatts, which is equivalent to about 4% of the country’s maximum generating capacity.

An outage at Huntly has seen Genesis divert gas to its coal or gas-burning Rankine units, one of which is pictured above.

Another 320MW of generating capacity was currently out for maintenance elsewhere, he said.

“This means we have 7% of the expected system capacity unavailable.

“This reduced total generation capacity means the system is now more susceptible to things going wrong during periods of particularly high demand, such as generation units failing to start or transmission outages.”

Nevertheless, generators were still able to meet demand on Wednesday evening last week, when electricity demand peaked at 7122MW and came within 7MW of topping the record set in August 2021, he said.

Jay said power companies had been cooperative,making their generation available when needed, and lines companies were managing controllable load during peaks as a part of their normal network management.

Genesis chief trading officer Pauline Martin said the company had diverted all the gas that was usually consumed by the Unit 5 turbine to its three Rankine turbines and had also bought in more gas on top that to power those.

The Rankine turbines are able to burn either gas or coal, and each has capacity of about 250MW.

One of the Rankine turbines appears to still be on coal, at least periodically, but Genesis’ coal usage has been low since the end of June.

“Since Unit 5 went on outage, Huntly Power Station has required just under 20,000 tonnes of coal,” Martin said.

“This compares with up to 220,000 tonnes per month necessary to meet New Zealand demand during a dry year when hydro lakes are low.”