Lake Onslow pumped storage

Comment by Earl Bardsley, University of Waikato (formerly Associate Professor in hydrology and Meridian Energy Senior Research Fellow in Applied Hydrology).

The proposed Lake Onslow pumped storage scheme in Otago (NZ) is modelled on the Saurdal scheme in Norway. The Saurdal scheme has a generating capacity of 640 MW and an upper reservoir energy storage capacity of 3.3 TWh. From full storage, it can generate at its maximum rate continuously for 7 months.  The Onslow scheme would have a generating capacity of 1000 MW and an upper reservoir energy storage capacity of 5 TWh. From full storage, it could generate at its maximum rate continuously for 6 months.

The multi-month generating capability of the Onslow scheme is valuable for buffering South Island dry years, where there can be a few months of low inflows into the hydro lakes. In effect, the Onslow scheme can be thought of as keeping the lights on in Dunedin and Christchurch while that South Island hydro power is now free to be diverted to the North Island. That is, dry year power is now from renewable sources instead of burning coal at the Huntly power station.

On shorter time scales of hours and days, Onslow’s 1000 MW of fast-response electricity would be used to smooth the fluctuating power from new wind and solar sources.

The Lake Onslow reservoir on February 21, 2023. Energy storage would be achieved by raising the lake to have an upper level about 80 metres above the present lake. Water would be pumped up from the Clutha River. Credit: Yasaman Karaminik.

After the October 2023 election, the new government announced that the detailed business case report that was being prepared by MBIE about the Onslow scheme would not be permitted to be completed. The present situation is that there still remains too little information for a future new government to make a decision about pumped storage at Lake Onslow. So the report would need to be then reactivated and completed. This would quantify the national economic benefits of the scheme over its 100 years of operational lifetime, to be measured against its estimated $16b construction cost.

Additional material

There are many pumped storage schemes either completed or under construction around the world, often motivated by the need to buffer expanding wind and solar power generation. Click on the world interactive map on this link.

An independent report that includes Lake Onslow pumped storage as a future electricity pathway option can be downloaded here.

There have been many misconceptions raised about pumped storage at Lake Onslow – like it is in the wrong island or that it will be a national energy drain. A listing can be downloaded here, along with responses.

Although now dated with respect to construction cost, a video overview can be found here.

The Lake Onslow pumped storage concept originated from work at the University of Waikato and in 2019 was recommended by the Interim Climate Change Committee for more detailed government investigation as a dry year mitigation possibility. The listing below is by way of recognition of contributing individuals.

Bardsley, W.E., Karaminik, Y., Majeed, M. (2022). Estimating Teviot River compensation flow to offset evaporation loss from Lake Onslow pumped storage. Journal of Hydrology (NZ), 61, p.179-182.

Kamarinik, Y., Bardsley, W. E. (2020). Onslow pumped hydro: environmental offsets and spinoffs. New Zealand Hydrological Society Annual Conference, Invercargill.

Majeed, M. (2019). Evaluating the potential for a multi-use seasonal pumped storage scheme in New Zealand’s South Island (PhD).

Bardsley, W.E., Majeed, M. (2015). A multi-functional large pumped storage scheme for New Zealand in support of renewable energy development? International Congress on Modelling and Simulation (MODSIM2015). Gold Coast.

Majeed, M., Bardsley, W. E. (2015). Assessment of economic and environmental advantages of a seasonal pumped storage scheme (Onslow, Central Otago). New Zealand Hydrological Society Annual Conference, Hamilton.

Majeed, M., Bardsley, W. E. (2014). Simulation models to evaluate economic feasibility of a possible seasonal pumped storage scheme at Onslow, Central Otago. Electricity Engineers Association Conference Wellington.

Majeed, K. M., Bardsley, W. E. (2012). Prospects for pumped storage in Central Otago. New Zealand Hydrological Society Annual Conference, Nelson.

Bardsley, W. E. (2006). A pumped storage scheme for maintaining hydro electricity against climatic variations? (Invited paper) 8th Annual New Zealand Energy Summit, Wellington.

Bardsley, W. E. (2006). China and New Zealand: Large seasonal pumped storage schemes for an electricity future using wind power and small hydro systems? International East Asia Regional Workshop of the International Academy Panel (IAP) on Water Security with Climate Change and Human Activity, Beijing.

Bardsley, W. E., Leyland, B., Bear, S. F. (2006). A large pumped storage scheme for seasonal reliability of national power supply? Electricity Engineers Association Conference, Auckland.

Bardsley, W. E. (2006). The Onslow seasonal pumped storage scheme revisited: An alternative approach to water level management of the southern hydro lakes? New Zealand Hydrological Society Annual Conference, Christchurch.

Bardsley, W. E. (2005). Note on the pumped storage potential of the Onslow-Manorburn depression, New Zealand. Journal of Hydrology (NZ), 44, p.131-135.

Bear, S. (2005). Hydrological evaluation of pumped storage in the Onslow-Manorburn basin (MSc).

Bear, S. F., Bardsley, W. E. (2004). A large New Zealand pumped storage scheme for reliable power through dry years? New Zealand Hydrological Society Annual Conference, Queenstown.

Bear, S. F., Bardsley, W. E. (2003). A pumped storage/thermal station hybrid for maintaining New Zealand electricity supply through dry years. New Zealand Hydrological Society Annual Conference, Taupo.






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