By Morteza Ghamgosar and David Lees

First published in the ANZ Journal October 2024

Foreword
Pumped storage schemes are not new – indeed Snowy 2.0 is a pumped storage scheme, and the Kidston Project is now well underway. However, they do seem to have become “flavour of the month” and such schemes as Big T, Big G are in the pipeline.

These projects are essentially developed around open pit mining projects and many such as Kidston involve a significant amount of new underground development. Hence an interest by the ATS.
There are opportunities here for many different disciplines as presented in this technical paper.

Introduction
Energy storage is becoming increasingly vital to our electricity system, and pumped hydro storage offers a promising solution for long-duration energy storage. This technology allows stored energy to be released into the market, balancing supply and demand effectively. One innovative application of pumped hydro is repurposing mining pits or residual voids for green energy purposes. Typically, these mine voids are left open and filled with water, serving little purpose without proper treatment. While there have been successful repurposing efforts both in Australia and internationally, many mine voids remain underutilized and are likely to persist indefinitely.

Energy storage plays a crucial role in ensuring a consistent electricity supply, even when conditions are unfavourable for solar or wind generation. During periods of high electricity demand or low renewable generation, water is released from the upper reservoir, flowing through an underground tunnel and passing through hydroelectric turbines to generate electricity. The water is then discharged into the lower reservoir, ready to be pumped back up when excess energy is available.

Australia, like many other countries, is focusing on the design and construction of pumped hydro projects. For instance, the country already boasts river-based pumped hydro energy storage facilities at Wivenhoe, Shoalhaven, and Tumut 3. Additionally, construction is well underway on the Snowy 2.0 project, which will add 2,000 MW of generation capacity to the National Electricity Market (NEM) and provide approximately 175 hours of storage. The Kidston pumped hydro scheme, located in an old gold mine in Far North Queensland, has secured funding from the Northern Australia Infrastructure Facility (NAIF). Furthermore, six additional pumped hydro energy projects have been shortlisted in the Underwriting New Generation Investments program.
This strategic use of existing mining infrastructure not only supports renewable energy initiatives but also transforms previously underutilised spaces into valuable assets for the future of energy storage [1].

Key elements in pumped hydro design: geotechnical engineering and hydraulics
Pumped hydro projects rely heavily on two main components in the realm of geotechnical engineering: rock mechanics and geotechnical features, as well as hydraulic or dam structures. Here, we delve into the critical aspects of rock mechanics and geotechnical investigations, which play vital roles in the design and construction of such projects.

Rock mechanics and geotechnical investigation
Beyond the hydraulic and mechanical elements, rock mechanics and tunnelling are the driving forces that dominate the design and construction phases of pumped hydro projects. Key considerations during the tender and commissioning stages include:

1. Geological and groundwater conditions:

  • Geological context: Understanding the geological setting is essential. Rock type, structure, and fault zones significantly impact excavation stability.
  • Groundwater conditions: Groundwater presence influences tunnelling processes and the design of rock support systems.

2. Excavation stability:

  • Rock mass stability: Ensuring rock mass stability during excavation is crucial. Engineers assess rock quality, joint orientations, and potential instability risks.
  • Stabilisation techniques: Techniques such as rock bolting, shotcrete, and grouting are employed to enhance stability.

3. Sample and in-situ testing:

  • Laboratory tests: Rock mechanics investigations involve collecting samples and conducting laboratory tests, including uniaxial compression and triaxial tests.
  • In-situ testing: Real-world data is obtained through in-situ testing methods like borehole pressure cells and convergence monitoring.

4. Rock reinforcement:

  • Designing rock reinforcement: Effective rock reinforcement designs (anchors, bolts) ensure long-term stability. Considerations include load-bearing capacity, corrosion resistance, and installation methods.

5. Pneumatically applied concrete (PAC):

  • PAC for rock support: PAC is used for rapid ground support in tunnels and caverns and can be applied remotely.

6. Machine hall and penstock testing:

  • Machine hall testing: Testing an enlarged machine hall to full dimensions assesses rock behaviour under load conditions.
  • Penstock testing: Full-scale penstock test chambers determine the feasibility of concrete-lined pressure tunnels

These geotechnical considerations are fundamental to the successful design and construction of pumped hydro projects, ensuring the stability and longevity of the infrastructure. By addressing these elements, engineers can develop robust and efficient energy storage solutions that contribute to a sustainable and reliable electricity system [2].

Crucial elements of dam design in pumped hydro projects

Dam design plays a critical role in pumped hydro projects, influencing their efficiency, safety, and environmental impact. Here are key aspects of dam design in these projects:

1. Structural integrity and safety

  • Foundation stability: Ensuring the dam is built on a stable foundation to withstand the pressures exerted by the stored water.
  • Materials and construction: Using high-quality materials and construction techniques to prevent leaks and breaches, ensuring long-term durability.
  • Seismic considerations: Designing the dam to withstand potential earthquakes, especially in seismically active regions.

2. Reservoir capacity and layout

  • Upper and lower reservoirs: Designing two reservoirs at different elevations to facilitate the movement of water between them. The capacity of these reservoirs determines the amount of energy that can be stored.
  • Water flow optimisation: Ensuring efficient water flow between reservoirs to maximize energy generation and minimize losses.

3. Hydraulic design

  • Turbines and tunnels: Designing the tunnels and penstocks (pipes) to guide water through turbines efficiently. The design impacts the overall efficiency of the energy conversion process.
  • Pump and turbine placement: Strategic placement of pumps and turbines to optimize energy use during pumping and maximize electricity generation.
  • Control systems: Integrating advanced control systems for real-time monitoring and management of water flow and electricity generation.

In summary, the design of dams in pumped hydro projects is pivotal to their success, affecting everything from energy efficiency and safety to environmental impact and economic viability.

Pumped hydro storage projects: driving Queensland’s energy future
In Queensland, pumped storage schemes hold immense potential, with the capacity to store up to 7 gigawatts (GW) of electricity. This amount is sufficient to power the entire state for a day before requiring recharging. These developments will not only create local jobs but also support the transformation of our energy system.
In September 2022, the Queensland Government established Queensland Hydro to design, deliver, operate, and maintain long-duration pumped hydro energy storage assets, which will be the cornerstone of the state’s energy transformation.

Pioneering projects in Queensland
Queensland is home to Australia’s first new pumped hydro storage plant in around 40 years, Kidston II, a 250MW facility currently under construction. This project is part of a broader spending plan announced shortly after Premier Annastacia Palaszczuk set a 70% renewable energy target by 2032. The plan also includes the Pioneer-Burdekin project and another hydro plant at Borumba Dam, with feasibility studies initiated in mid-2022. Another noteworthy project is the Mount Rawdon Pumped Hydro Project, developed by a joint venture comprising Mt Rawdon Operations Pty Ltd (a subsidiary of Evolution Mining) and an investor group managed by ICA Partners. The goal is to generate 20,000 MWh of electricity from the existing open pit mine nearing the end of its life. The joint venture is currently undertaking a feasibility study to assess the potential for this pumped hydro facility.

Innovative potential projects for Queensland

Djandori Gung-I (Flavian) pumped hydro project

  • Developed by Sunshine Hydro in central Queensland.
  • An upper reservoir at approximately RL600 m and a lower reservoir at approximately RL165 m, connected by an access tunnel, tailrace/waterway tunnel, drop shafts, a power generation cavern, and a surface chamber.
  • Reservoirs formed by constructing zoned rockfill embankments.
  • Sunshine Hydro’s proprietary technology, AESOP (Advanced Energy Storage Optimising Program), uses historical, live, and forecast data to intelligently meet energy demands and firm green energy.

Big T

  • A 400 MW proposal in southeast Queensland developed by BE Power.
  • A new upper reservoir on Mt Sevastopol, underground water conveyances, and intake/outlet infrastructure connecting the upper reservoir to the existing Lake Cressbrook (lower reservoir).
  • Featuring an underground power station cavern housing two 200 MW reversible turbines.
  • Applications for necessary permits and approvals are in progress, with an Initial Advice Statement being prepared for submission to the Queensland Office of the Coordinator General.

Big G

  • A 800MW pumped storage project being developed by BE Power.
  • The estimated $2.3 billion project is located at Mount Alma in central Queensland.
  • The site was specifically selected due to two natural reservoirs with a height differential of 290 meters spaced less than two kilometers apart.
  • Construction is expected to commence in late 2027 with commercial operations anticipated to start in early 2033.

Pioneer Valley

  • Developed by Queensland Hydro in the Pioneer Valley near Mackay in central Queensland
    Key contracts for the5 GW/120 GWh Pioneer-Burdekin project have already been awarded

Borumba

  • Developed by Queensland near Gympie in the state’s southeast.
  • The business case for the 1 GW / 24 GWh scheme has been signed off by the government and the environmental approvals process is underway.
  • Involves expanding an existing lower reservoir and creating a new dam at a higher altitude, connected by an underground power station.
  • Water will be pumped to the upper dam during periods of surplus renewable energy and low demand, and then released back to generate electricity during times of high demand.
  • The underground works package includes the development of an access tunnel leading to the proposed site of the underground powerhouse cavern. The tunnelling will allow Queensland Hydro to gather geological, geotechnical and hydrogeological data to confirm the proposed location for the underground powerhouse and transformers caverns.
  • Data gathered during the tunnelling operation will complement surface geological investigations, helping inform design and delivery of the project.
    If the project proceeds, the tunnel will likely be repurposed to become one of the access tunnels required in the project design.

Mount Rawdon pumped hydro project

  • A proposed 2 GW / 20 GWh project being developed near Bundaberg.
    Potential gold mine transformation
  • Australian miner Evolution Mining is moving on a $7 billion plan to build a 2 GW / 20 GWh pumped hydro electricity generation facility in the pit of a 20-year-old gold mine in southeast Queensland.

References
1. https://www.aph.gov.au/
2. Brady, Barry HG, and Edwin T. Brown. Rock mechanics: for underground mining. Springer science & business media, 2006.
3. https://www.energy-storage.news/
4. https://mtrawdonhydro.com.au/