Energy Minister Megan Woods has released a preliminary report on the ‘NZ Battery’ (Project Onslow) investigation – see here.
She is due to present the final investigation report to Cabinet in December. At this stage it looks as though a very large (1,500 MW) power station would be a possibility:
“The various tunnel options could support up to 1,500 MW, with up to six turbines/pumps of 250 MW each. For comparison, New Zealand’s largest hydro plant is Lake Manapōuri, with installed capacity of 850 MW. Huntly power station has a total installed capacity of 953 MW.”
Transpower has confirmed that a pumped hydro scheme could integrate into the grid by connecting to nearby high-voltage lines.
If it goes ahead, it looks likely to be a major disruptor in the energy market, with very uncertain pricing implications. Apparently MBIE are working on a wider ‘Energy Strategy’ that may tell us more:
51 Conversely [i.e. vs just using pumped storage for dry year security], operating on a continuous basis means that the asset can be used much more efficiently, and support security of supply through a broader range of system challenges (including future calm, cloudy periods, and events like that on 9 August 2021). If operated on a continuous basis, it could be broadly revenue positive, though will have significant variability in its revenue between wet years (where it would be a net consumer of electricity as it pumps and stores energy) and dry years (where it would generate and draw down on its storage).
52 Questions of the operation and ownership of a pumped hydro scheme are complex. These issues will be considered at a high level as part of the current feasibility phase of the NZ Battery Project, but they would need to be investigated in fuller detail as part of any subsequent stage.