Effective water storage in the minerals sector is essential for operational efficiency and can enhance renewable energy platforms when projects reach the end of their life cycle.
Research from Spain’s University of Oviedo and industry consultant SADIM Ingenieria in the early 2020s demonstrated that underground pumped hydroelectric storage (UPHS) is both efficient and flexible for integrating intermittent renewable energy sources like solar and wind.
Abandoned open pits and tailings dams have also shown effectiveness with this technology, allowing mine water to generate energy and store surplus power from renewables.
Many existing water bodies are located in socially and culturally significant areas, making repurposed mining sites and underground tunnels viable. alternatives for pumped hydro reservoirs.
Closed mines are typically situated near transmission routes, have road access, and are conducive to managing evaporation and seepage. Additionally, these areas are often cleared of vegetation, making them suitable for at least one reservoir.
A typical UPHS plant consists of an upper and lower reservoir connected by a driving line and a pump turbine unit.The potential energy in the upper reservoir can be converted to electricity based on demand.During off-peak times, water is pumped from the lower to the upper reservoir using grid electricity.
During high demand, the water flows back down through the turbines to generate electricity.The storage capacity of the plant depends on the height difference between the reservoirs and the volume of water stored.
The researchers noted several key features of this technology, including a short start-up time (known as fast ramping) and a cycle efficiency ranging from 70-80 per cent, with some instances reaching 87 per cent.
Economically, this storage system capitalises on the price differences of energy throughout the day.“When the price is low, the energy is consumed from the grid to pump water from the lower reservoir to the upper one.
“When the price is high, the water drops from the upper reservoir, driving the turbine to produce electricity, which is fed back to the grid. In other words, energy is sold on the market at a higher price than it is bought.”
To be economically viable, the selling price must be at least 1.4 times higher than the pumping price, assuming 70 per cent efficiency. In 2020, the Australian government, alongside the New South Wales government and the AustralianRenewable Energy Agency (ARENA), conducted a technical review and pilot trial of pumped hydro energy technology at Centennial Coal Company’s underground Newstan coal operation, which had been closed for six years.
This study assessed the feasibility of retrofitting sealed coal mine goafs for UPHS and evaluated the practicality of operating within an active coal mine.
The research found that UPHS was technically viable only under specific conditions: longwall goafs needed to consist of high-strength rock at relatively shallow depths to minimise collapse risks, and the coal seams required low gas content and minimal risk of spontaneous combustion.
Several challenges arose during the initial project stage. For instance, it was unlikely that a pumped hydro energy scheme could operate concurrently with long wall extraction. Additionally, planning laws did not consider the useof underground coal mines for UPHS.
ARENA highlighted the need for regulatory collaboration.“Whilst planning approval pathways were identified, work would be required with government regulators to confirm permissibility once a definitive project is identified,” the agency said.
“As (pumped hydro) may produce fugitive emissions, the risk that a carbon tax or alternative emissions scheme is introduced will impact economics.”
Despite these challenges, Genex Power is advancing a 250-megawatt pumped storage hydroelectric facility at the decommissioned Kidston gold mine inQueensland, scheduled for completion in 2025. This $777 million project aims to serve as a natural battery, allowing energy to be stored and dispatched on demand.
It features an upper reservoir formed by a 20-metre high dam around the Wises pit, a lower reservoir utilising the Eldridge pit, a powerhouse cavern capable. of generating 250 MW, as well as a spillway from the upper reservoir to the Copperfield River.
The technical feasibility and collaborative design process took approximately four years, involving significant underground infrastructure. Once completed, the facility is expected to generate enough power to supply over 100,000 homes for eight hours during peak demand.
An article published in Renewable Energy last year noted that pumped hydro energy storage is currently the largest source of energy storage in the electricity industry, capable of meeting robust demand for overnight and longer storage.
This approach is not only low-cost but also has a minimal environmental footprint compared to traditional on-river systems. Meanwhile, batteries are likely to dominate storage for short durations, from seconds to hours.
