One of the alternatives to a gigantic hydroelectric power station at Lake Onslow in Otago is a similar scheme at Upper Moawhango, near the Waiouru Military Camp.

A briefing to Energy Minister Megan Woods, released to Newsroom under the Official Information Act, shows the minister held a hui with local iwi in September to discuss the concept. In a letter to iwi, Woods said the Government was keen to do “some more high-level research into a pumped hydro scheme on the upper Moawhango River. The focus of this research would be to explore whether it’s technically viable and gain an understanding of the cultural and commercial impacts it may have.”

A spokesperson for Woods declined to comment.

While the NZ Battery project is looking at a range of pumped hydro and non-hyrdo solutions to New Zealand’s dry year problem, in which low precipitation could limit the output of our hydro stations and force fossil fuel to pick up the slack, Lake Onslow is the Government’s clear favourite.

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Pumped hydro bypasses the reliance on precipitation by creating a two-basin scheme, where water is pumped into an upper basin when power is plentiful and then released into the lower one to generate electricity in a dry year.

The project at Moawhango would be pumped hydro as well.

Niwa conducted a nationwide review of locations with suitable geographic features for pumped hydro and a consultancy called StanTec looked over these to see which might have merit. One spot on the upper Moawhango River was “deemed appropriate to investigate further”, according to talking points drafted for Woods for the hui, with few others being found to be viable.

One benefit of a North Island project would be that it is closer to most electricity demand, which comes from Auckland. Officials advised the land affected is mostly owned by the Defence Force, with some conservation and private land also involved. It would have an impact on the Tongariro hydroelectric power scheme, owned by Genesis, which declined to comment for this article.

In 2021, Stuff reported that Genesis had approached the Government with the idea for a pumped hydro plant on the Moawhango, but nothing had been heard since. At the time, hydrologist Earl Bardsley told the outlet the project could completely obviate the need for Lake Onslow.

Officials told Woods in the briefing released to Newsroom that there is still considerable grievance among iwi in the area about the development of the Tongariro scheme, which was done largely without consultation. That lack of consultation has been subsequently found to be a breach of the Treaty of Waitangi. They recommended iwi engagement was needed before any further work was conducted on the pumped hydro idea.

Bardsley, who first suggested the idea of a pumped hydro scheme at Lake Onslow two decades ago, told Newsroom he now wasn’t sure whether an Upper Moawhango scheme would be large enough to address the dry year risk.

“I would say that the Moawhango project falls in the cracks between storage and peaking and doesn’t really achieve either,” he said.

“I appreciate that I don’t know the detailed specs of what’s going on. I mean, I can only look at the topo map. But I did have a look previously at the Moawhango and in principle, certainly, if you were willing to put a great big tunnel through to Lake Taupō, you could get that significant amount of storage. But that would be enormously expensive.

“The Government has specified that for its dry year storage it wants between three and five terawatt hours. I just don’t see that you can get three terawatt hours from a localised pump storage scheme without having a much bigger drop down to a lower elevation like Lake Taupō.”

Marc Daalder is a senior political reporter based in Wellington who covers climate change, health, energy and violent extremism. Twitter/Bluesky: @marcdaalder

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