Rain falls and hydro lakes go up

South Island hydro lakes are now above the 91-year average for the first time since early May.

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

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

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

“Pukaki is still well below average but steadily building, while the rapid rise in Lakes Manapouri 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,” he says.

“That means we can rely on strong generation out of Manapouri Power Station while Pukaki refills. Things are continuing to look more positive, but there’s still some way to go.”

Snow storage in the Waitaki catchment has increased to 86% of average, up from 83% last week. Snow melt contributes significantly to Waitaki catchment inflows over the summer.

Meridian’s six wind farms continue to perform well, generating 41GWh during the week.

Strong winds and increased hydro generation meant average wholesale prices (also known as spot prices) of $19/MWh in North Island and $17/MWh in the South Island, with extended periods of prices sitting just above $0.00/MWh in both islands, says Meridian. “This has been the case for the last three weeks.”

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.

\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 44MW of generation potential,” says Ewers.

“This winter’s demonstrated the importance of every single megawatt, and we’re very grateful to Transpower for their generosity and flexibility.”

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