By Timothy Weber and Professor Andrew Blakers, Australian National University
The world is rapidly moving towards a highly electrified, renewable energy future and the mining industry has a key role to play in the transition.
When it comes to generating electricity, solar photovoltaic and wind have effectively won the energy race. Solar and wind inherently need energy storage systems that can be charged when there is a surplus of electricity supply and discharged to fill the gaps when the sun is not shining and the wind is not blowing.
Mine sites offer an opportunity at their end-of-life to be repurposed into low-cost pumped hydro energy storage systems, providing reliable firm power for the electricity grids of the future.
Recognising this, a team of researchers from the Australian National University (ANU) created a series of atlases that highlights former mining sites that have the potential to host pumped hydro storage.
The fastest energy change in history
Around the world, solar and wind made up approximately 84 per cent of new generation capacity added to electricity grids in 2023. Annual solar installations are doubling every three years, and solar and wind are now the cheapest form of new electricity.
Any other low-carbon technology, including nuclear and carbon capture and storage, would require extraordinary growth rates to become competitive with solar and wind to meet decarbonisation targets.
Figure 1 utilises IRENA, IEA, World Nuclear Association and Global Energy Monitor data to display annual installations of electricity generation technologies globally.
In the Australian National Electricity Market, about 40 per cent of electricity is currently generated from renewable sources. The Federal Government has set a target of 82 per cent renewables by 2030 and established the Capacity Investment Scheme to secure 32GW of renewable capacity to meet this target. Almost all of this renewable generation will come from solar and wind, as this is almost all that is being built at the moment.
According to the Australian Energy Market Operator (AEMO), electrification of transport, heating, cooling and industry could double electricity demand, and a large hydrogen industry could double it again. Australia is in the middle of the fastest energy change in history.
Off-river pumped hydro energy storage
Rapidly rising electricity demand coupled with the low cost of solar and wind generation means that most of Australia’s electricity supply will be variable. This means that when the sun does not shine or the wind does not blow, many of these generators will not be able to produce new electricity. It is essential to integrate energy storage systems into the grid to fill the gaps in electricity supply.
According to various analyses from ANU, AEMO, and the Commonwealth Scientific and Industrial Research Organisation (CSIRO), Australia may require between 480–1050GWh of energy storage by 2050. The actual amount will depend on the level of grid interconnection and the size of Australia’s hydrogen production economy.
Pumped hydro energy storage is currently the cheapest form of overnight storage. It is a mature technology that constitutes about 95 per cent of all existing electrical energy storage around the world. These pumped hydro systems are complementary with batteries, which excel at short-duration storage on the scale of seconds-to-hours. A future electricity grid would benefit from hybrid storage configurations, where pumped hydro can trickle-charge high-power batteries, allowing them to meet peak demand at a low cost during the day.
Most possible pumped hydro sites are located off-river. They are formed using a pair of reservoirs with a large elevation difference (called the ’head’) connected by a high-pressure tunnel. When there is excess generation in the grid, water can be pumped from the lower to the upper reservoir. Later, the water stored in the upper reservoir can be released through a turbine to fill the gaps in electricity supply. Since these systems are off-river, they form a closed loop that recycles the water up and down for up to 100 years.
Off-river pumped hydro systems do not involve any new dams on rivers. This unlocks an enormous number of options for sites far away from rivers with very large head and small dam walls. Doubling the head, in turn, doubles the energy storage, dramatically reducing the cost per unit of energy storage. Off-river sites generally have a low environmental footprint compared to on-river systems. Due to the lack of cooling towers and fuel processing, a 100 per cent renewable energy system mostly consisting of solar, wind and pumped hydro also requires far less water than a comparable fossil fuel-based energy system.
The 100% Renewable Energy Group at ANU has been developing Global Pumped Hydro Energy Storage Atlases that locate possible sites for off-river systems outside large urban areas. These atlases account for over one million unique options around the world. The recently developed Brownfield Atlas focuses on mining pits, pit lakes and tailings pods that have the potential to be paired with a nearby upper reservoir, forming a cheap and convenient pumped hydro system.
Converting mine sites
Mine sites have the benefit of existing infrastructure that can be repurposed for a ‘brownfield’ pumped hydro energy storage system; one of the reservoirs has already been cleared and dug through the original mining operations. Mines also require electricity transmission, major road access, nearby accommodation for developers and operators and water sources and licences for their operation, all of which can be rolled into the development and operation of a pumped hydro system.
Building new transmission is one of the main bottlenecks for Australia’s renewable energy transition due to the need to negotiate with large numbers of private landholders. Therefore, existing onsite transmission infrastructure can greatly streamline the development of brownfield pumped hydro compared to other types of reservoirs.
Just having a large mining pit, however, is not enough for a pumped hydro system.
A nearby location with a higher elevation must also be found for the upper reservoir. The ANU group used a global dataset of terrain elevation to model reservoirs and pair them with nearby mining pits. The sites with large head, large reservoir volumes relative to the dam wall size (water-to-rock ratio) and small separation distances are all recorded in the Brownfield Atlas. Each site is assigned a ‘cost class’ from AAA to E, with a class E site costing roughly six times more than a class AAA site.
Although mining sites have a lot of great features that help to simplify the development of a pumped hydro system, they are not without their own unique challenges. One such challenge is that mining pits are often in possession of steep conical sides. Additionally, rapidly changing the water level can strain the walls of the mining pit and put pressure on the turbines, limiting the water volume that can be practically used for energy storage. Contaminants within the mining site, such as sulphides, could corrode pumped hydro components or contaminate freshwater ecosystems if they seep into the environment. These technical challenges may require designs that incorporate reinforcement of unstable slopes and reservoir linings to prevent water seepage.
There is also the risk of the land surrounding active mining sites containing additional mineral reserves, making mineral rights an essential consideration for the impact of future mining on the pumped hydro system. Mining pits are also typically smaller and more geographically constrained compared to new greenfield pumped hydro systems where both reservoirs are built on undeveloped land. This smaller size makes them ideal for providing overnight storage of solar generation but limits their ability to provide seasonal storage during the winter.
Some combination of pumped hydro systems consisting of brownfield, greenfield and sites that repurpose existing lakes and reservoirs (bluefield) will be necessary to support a transition to 100 per cent renewable generation.
The pumped hydro boom
The last pumped hydro system completed in Australia was Wivenhoe Power Station in 1984. Recently, the development pipeline has exploded with new pumped hydro projects as solar and wind generators have rapidly connected to the grid.
In Australia, there are at least 23 pumped hydro projects with 21,000MW/ 660GWh of storage at various stages of investigation and development that have been publicly announced. Snowy 2.0 makes up almost half of this prospective energy storage, with completion expected by 2028.
One of the earliest examples of a brownfield pumped hydro system is Dinorwig Power Station, completed in 1984 in northern Wales, repurposing an old slate quarry. In Queensland, the Kidston Pumped Storage Hydro Project (250MW/ 2GWh), which repurposes two adjacent mining pits, is due to be completed at the end of 2024. Muswellbrook Pumped Hydro (500MW/ 4GWh) and Mt Rawdon Pumped Hydro (2000MW/ 20GWh) are other brownfield sites that are also undergoing feasibility studies.
Pumped hydro of the future
The Brownfield Atlas produced by ANU located 904 mining sites in 77 countries which could be repurposed as pumped hydro systems at their end-of-life. Of these sites, 37 were in Australia with a total energy storage potential of about 540GWh.
It is unlikely, however, that all 23 pumped hydro projects in Australia’s pipeline will be determined to be feasible. Thankfully, the potential sites on the Global Pumped Hydro Energy Storage Atlases, including the Brownfield Atlas, provide 100 times more energy storage than what would be required for Australia to support a 100 per cent renewable energy system. This means that developers can afford to be picky – if one site is deemed infeasible, then there are thousands of other good-quality options available to choose from.
Renewable generation and energy storage are a solved problem. Off-the-shelf technologies such as solar, wind, pumped hydro and batteries are the backbone of the energy transition. There is no need to wait for dramatic improvements in technology; this means Australia can just focus on getting the job done.
Featured image: 84 per cent of Australian brownfield pumped hydro options (red) are within 10km of existing transmission lines. Image: ANU, using transmission information from Geoscience Australia, original map sourced from Google Basemap.
