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Project overview
  • Lead Organisation

    Centennial Coal Company


    Fassifern, New South Wales

    ARENA Program

    Advancing Renewables Program

  • Start date

    7 January 2021

    End date

    1 May 2022

  • Project Partners
    NSW Government, Byrnes Geotechnical, University of Newcastle, GHD
    This renewables project has been discontinued.


The Centennial Pumped Hydro Energy Storage project will perform a series of technical studies and trials for the potential deployment of a nominal 600 MW pumped hydro energy storage (PHES) system using underground coal mining voids.

Key results

The project determined that underground PHES would only be technically viable under a set of very specific conditions:

  • Suitable longwall voids will need to be composed of high strength rock and be at relatively shallow depths so saturation-induced collapse is minimal.
  • The longwalls will need to be relatively narrow so that there are relatively more high porosity/conductivity edges.
  • The coal seams mined will need to have very low gas contents and a low propensity to spontaneous combustion.

The following challenges were identified during the first stage of the project:

  • It is unlikely that a PHES scheme can be operated concurrently with longwall extraction and that the infrastructure required for PHES can be installed while mining in anticipation of such a scheme later.
  • Planning laws have not envisaged an underground coal mine being used as an underground PHES. While planning approval pathways were identified, work would be required with government regulators to confirm permissibility once a definitive project is identified.
  • As underground PHES may produce fugitive emissions, the risk that a carbon tax or alternative emissions scheme is introduced will impact economics.


The Centennial Pumped Hydro Energy Storage project acknowledges that Large-scale PHES can firm up intermittent renewable generation. It provides flexibility and balancing management allowing the market operator to ensure security and reliability given a high (>50%) integration of renewable intermittent generation. AEMO’s Integrated System Plan 2020 suggests the NEM will require 6-19 GW of storage by 2035.

It is estimated that underground coal mining PHES, when compared to traditional PHES, could result in significant cost reductions driven by the lower cost of civil construction works (due to the pre-existing lower reservoir and existing underground shafts) as well as benefiting from being located close to the strong areas of existing transmission infrastructure associated with incumbent coal fired power generators.


Through performing a series of technical studies and trials the project will test the potential deployment of a PHES system using underground coal mining voids. If successful, Centennial Coal will conduct a detailed engineering design and feasibility study which will culminate into a Final Investment Decision (FID) for one of its Lake Macquarie sites. The construction would be a first-of-kind underground PHES deployment.


The project aims to increase skills, capacity and knowledge of renewable energy technologies by improving the understanding of the technical feasibility and risks of underground PHES, including determining whether a coal mining void is viable as a lower reservoir option for PHES facilities; increase the value delivered by renewable energy by indicating the key materials and designs of turbines and maintenance requirements for successful PHES facilities utilising coal mining void as lower reservoirs; and improve the understanding of the commercial advantages that underground PHES may contribute to the reduction in cost of renewable energy.

Last updated 26 September 2022


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