Meridian says South Island hydro levels now at above-average levels

Meridian's hydro lakes are in better shape after heavy rain in the South Island. Photo / NZME

Meridian’s South Island hydro lakes are now above their 91-year average for the first time since early May, the company says.

Persistent rain has seen Lake Pūkaki rise by about two metres since its lowest point in late August, with a further 80-160mm of rain forecast over the coming days.

South Island averages have been boosted by huge inflows into Lakes Manapōuri and Te Anau, with both at the top of their ranges and another 200mm of rain forecast this week, the company said.

Very low lake levels and gas supply constraints pushed wholesale power prices over $800 per megawatt hour (MWh) last month, but recent rain and an agreement to buy gas off Methanex have taken the pressure off the spot market.

“Bit by bit, our hydro storage is increasing,” Chris Ewers, Meridian’s general manager wholesale said.

“Pūkaki is still well below average but steadily building, while the rapid rise in Lakes Manapōuri and Te Anau is due to their smaller storage capacity.

“It’s like the difference between a swimming pool and a bath – one’s much faster to fill because it holds much less water.

“That means we can rely on strong generation out of Manapōuri Power Station while Pūkaki refills.”

Ewers said the outlook was more positive, but there was still some way to go.

Snow storage in the Waitaki catchment had increased to 86% of average, up from 83% last week.

Snow melt contributes significantly to Waitaki catchment inflows over the summer period.

Meridian’s six wind farms continue to perform well, generating 41 gigwattt hours (GWh) over the week.

Strong winds and increased hydro generation meant average wholesale prices of just $19/megawatt hour (MWh) in the North Island and $17/MWh in the South Island, with extended periods of prices sitting just above $0.00/MWh in both islands.

Meridian’s wind generation is also set for a further boost thanks to an agreement with Transpower for the loan of a transformer to West Wind Farm at Mākara, west of Wellington.

West Wind has been running around a third below maximum capacity since one of its transformers failed in May 2023.

The temporary replacement is being installed in mid-October.

Being back to two transformers at West Wind means an extra 44 megawatts of generation potential, the company said.

A permanent replacement is expected to arrive at West Wind Farm in mid-2025.

Last month’s high spot prices have put some energy-intensive businesses under pressure.

Winstone Pulp International has said its Tangiwai Sawmill and Karioi Pulpmill in the central North Island may have to close due to higher prices.

A decision on the mills’ future is due today.

Jamie Gray is an Auckland-based journalist, covering the financial markets and the primary sector. He joined the Herald in 2011.