Drought conditions threaten Southland’s power supply

It was feared that the Manapouri hydroelectric plant would not be able to supply power to Southland because water levels in the lake had fallen below the operating range.

Barry Harcourt

It was feared that the Manapouri hydroelectric plant would not be able to supply power to Southland because water levels in the lake had fallen below the operating range.

The usually wet Fiordland was so dry this summer that Transpower New Zealand feared water levels in Lake Manapouri were dropping too low to generate electricity from the hydroelectric station.

The company reconfigured the national grid, so that electricity could be drawn from stations further north in the event that demand exceeded supply in the Southland.

Agriculture Minister Damien O’Connor classified drought conditions in Southland, Clutha and Queenstown Lakes districts in late March as a medium-scale adverse event.

Lake Manapouri received just 82mm of precipitation in March, just 26% of its normal monthly rainfall and the second lowest volume recorded since 1971.

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National MP Stuart Smith asked Energy and Resources Minister Megan Woods in a Parliamentary Written Question whether this meant less electricity would be produced by the Manapouri hydroelectric plant.

Water levels in the lake had fallen to a level that meant the rate at which water was taken from the lake had to be carefully managed, Woods said.

“A risk is that Southland’s regional demand … could exceed the capacity of the grid to transmit electricity into the region from generation outside the region,” Woods said, adding that Transpower had reconfigured the national grid. to ensure that the region was not dependent. on Lake Manapouri.

Energy and Resources Minister Megan Woods said poor rainfall in Southland meant Transpower was preparing to source power from elsewhere in the country to supply the region. [File photo]

Robyn Edie / Stuff

Energy and Resources Minister Megan Woods said poor rainfall in Southland meant Transpower was preparing to source power from elsewhere in the country to supply the region. [File photo]

The hydroelectric plant is owned by Meridian and a spokesperson explained that the plant supplied the national grid – which was managed by Transpower – to supply Southland.

On March 30, Meridian decided to reduce the flow of Lake Manapouri from the normal minimum of 115 cumec per second to a limit of 80 cumec to minimize the environmental impact of light rains.

Transpower’s chief operating officer, Dr Stephen Jay, said water levels in the lake had begun to drop below the normal operating range (between 176.8 and 178.6 meters above sea level). sea) in March.

“As the situation worsened in late March and early April with very little rainfall, there was a risk that the lake level would fall to levels where Manapouri could no longer generate electricity,” he said.

Transpower's Chief Operating Officer, Dr Stephen Jay, said lake levels are likely to fluctuate more in the future as climate change impacts rainfall patterns.

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Transpower’s Chief Operating Officer, Dr Stephen Jay, said lake levels are likely to fluctuate more in the future as climate change impacts rainfall patterns.

The network was reconfigured on April 8, but this also led to “regional security problems” with the risk that lines or transformers could reach their thermal limits when large amounts of energy were transferred.

“Local voltage issues can also arise when there are high loads in low-generation regions,” Jay said.

To mitigate this, Transpower introduced a voltage stability constraint to stabilize the electricity flowing through the grid area at the bottom of the South Island south of Clyde.

The network’s normal configuration was restored on April 28 after Lake Manapouri returned to its main operating range in mid-April, Jay said.

Data from the National Institute for Water and Atmospheric Research shows rainfall has not been sustained and overall rainfall has been below normal with Lake Te Anau – which feeds Lake Manapouri – 87%.

However, Milford Sound recorded 211.5mm of rain at 9am on April 21 – its wettest April day in seven years, or since April 2015.

It is expected that network reconfiguration will become more frequent in the future.

“We predict that climate change will cause less but greater rainfall, which means lake levels could fluctuate more throughout the year than they do now,” Jay said.

Alan A. Seibert