Transpower's ability to shift electricity north just got a lot better

Transpower's Clutha Waitaki project will mean power can shift more freely northward from the lower South Island. Photo / Supplied

Transpower's ability to send electricity from the lower South Island northwards has just got a lot better with the completion of the Clutha to Upper Waitaki Lines Project (CUWLP).

Rio Tinto, the majority owner of New Zealand's biggest power user - the Tiwai Point aluminium smelter - has said it plans to close the plant at the end of 2024.

There is conjecture as to whether it will follow through on that, given the current high aluminium prices.

With Tiwai representing 13 per cent of New Zealand's power consumption, its closure would make a lot more power available but without upgraded lines, Transpower's ability to send it north would have been constrained.

"The total project has nearly doubled the transmission capacity of the network for transfer northwards – particularly important for either new generation in the area or the potential closure of the aluminium smelter at Tiwai," the state-owned grid operator said.

The 142km section of transmission line, between Roxburgh in Central Otago and Livingstone in the Waitaki Valley, has been duplexed, a process in which the single electrical wire per phase has been replaced with two wires.

This, together with other work as part of the wider project, has increased the northward transmission capacity for New Zealand from around 600 megawatts to about 1100 MW.

Transmission projects of this type and size normally take several years to complete, Transpower said.

In this case, with the threat of Tiwai closure, the project took just 18 months.

The final section of the project traversed the remote Danseys Pass which offered tricky terrain and variable weather.

CUWLP spanned many years – with final works held over initially until the economics of undertaking them improved.

A key driver for restarting in the last couple of years was the possibility of the Tiwai aluminium smelter closing.

The first two components were delivered in 2015 and 2016, and in 2020 Transpower completed the third component, a thermal upgrade of the Cromwell to Twizel section of the Roxburgh-Twizel 220kV transmission line.

The project was a significant part of Transpower's support to shift New Zealand to electrification and a low carbon economy by 2030.

Transpower's general manager grid development, John Clarke, said the project is the first of many works expected over the medium term to facilitate that shift.

Transpower has investigations under way to improve its capacity in the Central North Island, around Wairakei, and the interisland HVDC submarine cables.

"All this and more will be needed as we move totally away from carbon to a renewable mix of energy sources – like hydro, wind, geothermal and solar," Clarke said.