Lake Onslow option

Pumped hydro storage at Lake Onslow is one option being explored.

Facts and figures for Lake Onslow project

The Lake Onslow option referenced by the Interim Climate Change Committee could be anticipated to provide at least 5TWh of annual generation/storage. It is estimated to have a construction timeframe of 4-5 years, with commissioning and filling taking a further 2 years. At its construction peak, it is expected to create 3,500-4,500 skilled and semi-skilled jobs.

What services can a pumped storage project like Lake Onslow provide?

  • Dry year storage—we are specifically investigating Lake Onslow given its ability to store up to 5-7TWh for dry year support
  • Intermittency back up—our existing hydro lakes can increase or decrease their output to offset the variation in wind or solar generation, but this capacity is limited. Pumped hydro could provide a form of back-up to ensure electricity supply and demand is met when generation from solar, wind and existing hydro are not enough.
  • Fast response reserve—pumped hydro can potentially provide technical services that ensure system stability in the electricity market.

What is the estimated cost of a project like Lake Onslow?

Early estimates indicate a project like Lake Onslow could cost about $4 billion. Our feasibility study will provide greater certainty about the costs.

How would it be funded?

Funding and financing models along with any potential subsequent levies, will be determined through the feasibility study. The use of a levy would need to be justified via a demonstration of significant public good in a feasibility study, including through overall lower prices for consumers in the long term.

Where is the Lake Onslow option located?

The Lake Onslow option is located north-east of the Clutha River in Central Otago.

The diagram shows what a 5TWh proposed lake would look like at the 760 metre contour. This is not the only possible option for Lake Onslow.

The NZ Battery Project is considering pumped hydro projects at a range of different locations, in addition to alternative technologies.

Map of the 5 TWh/760 metre countour option at Lake Onslow.

Contracted work

In October 2021, the Energy and Resources Minister announced a significant contract to investigate the engineering, environmental planning and geotechnical feasibility investigations at Lake Onslow had been awarded to Te Rōpū Matatau.

Te Rōpū Matatau is a consortium of firms led by engineering consultancy Mott MacDonald New Zealand, with engineering consultancy GHD and environmental planning and design consultancy Boffa Miskell.

This work, along with the environmental and cultural investigations already underway, will give a better picture of the feasibility and costs of the Lake Onslow storage scheme.

Te Rōpū Matatau’s Lake Onslow feasibility study is divided into 2 segments – Part A and Part B – which are part of first phase of the NZ Battery Project.

Part A largely focuses on desktop studies that look into possible designs of the scheme, the environmental effects and determine the geotechnical fieldwork programme in Part B.

Part A is expected to be completed before a Ministerial decision in about May 2022.

Early field work is required during Part A to establish key elements of feasibility and cost for an in-principle decision in May 2022. These elements include information on nearby availability of material for dam construction, geology of the possible dam wall area and better understanding of tunnelling costs. At this point, Ministers will have preliminary geotechnical information, a preferred design option or options, and an understanding of the environmental, cultural and social implications of a pumped hydro scheme at Lake Onslow.

Part B of Te Rōpū Matatau’s feasibility study includes further geotechnical and engineering field work to understand the regional geology, rock properties and fault lines and determine the best possible location and design.

The fieldwork investigations are likely to include drilling shallow and deep boreholes to better understand the underlying geology, the best route for a tunnel and the best location for a potential underground powerhouse.

The environmental planning work will also look at consenting options and what further work may be needed to assess the environmental effects.

These geotechnical, engineering and environmental studies are required to provide a further level of certainty for a full feasibility-level decision by Ministers, currently planned for December 2022.

Last updated: 05 November 2021