Sleeping beauties: Is there a future for disused mines?

A wasted opportunity? Closed gold mines like this one in Queensland can still have untapped reserves. Credit: Jason Stock Photograph/Shutterstock.

Recently, the mining industry has looked to concentrate on optimisation and new forms of production through AI, but this tends to ignore the dormant, yet ever present need to optimise vacant and disused mines too.

These can be converted to various forms of renewables, thereby cutting emissions and remedying ESG issues from disused sites, all the while optimising up risk and opportunity as a whole in Australia. What does optimisation for vacant mines mean, and what's the best way to go about it?

The fascinating thing about mines, both in Australia and globally, is that once built and left vacant, they are simultaneously dangerous and inherently useful.

ESG concerns surround both the health and safety of disused mines for locals, the potential for pollution leaks, potential for collapse, water contamination from old equipment or even the build-up of toxic gases. A disused mine, in most cases, isn't a particularly safe place.

Then again, flooded water in mines is often naturally heated by geothermal action. Mines are more than holes in the ground. Once you've realised this, a whole host of technologies across heat source pumping and heat exchangers can make the most of such stored energy, in arguably as valuable a way as the original hydrocarbons housed therein.

Heat remediation is an obvious solution. Perhaps a less well-known option surrounds the potential for the depth of Australian mines to be leveraged in hitherto unimagined ways. Recent research from the International Institute for Applied Systems Analysis (IIASA) argues that the speed of fossil fuel phase out and the growth of zero-carbon solutions will now determine the future of billions of people.

The authors say that current global governance is inadequate for the scale of the challenge and make six key recommendations to change course fast, including coordinated action to trigger positive tipping points.

“Similar to tipping points in the Earth system, positive changes can build on one another,” notes IIASA researcher Caroline Zimm, who co-led one of the four sections of the report.

“Think about it like this: if electric cars become the most popular kind of road transport, this can lead to advances in battery technologies leading to better and cheaper batteries. These improved batteries might then also open up opportunities that allow for storing energy from renewable sources.” This type of joined-up, circular thinking is evident in a similar IIASA study, which examines the potential for Underground Gravity Energy Storage (UGES).

Essentially, UGES turns decommissioned mines into long-term energy storage solutions, thereby supporting the sustainable energy transition.

UGES generates electricity when the price is high, by lowering sand into an underground mine and converting the potential energy of the sand into electricity via regenerative braking and then lifting the sand from the mine to an upper reservoir using electric motors to store energy when electricity is cheap.

The main components of UGES are the shaft, motor/generator, upper and lower storage sites, and mining equipment. The deeper and broader the mineshaft, the more power can be extracted from the plant, and the larger the mine, the higher the plant's energy storage capacity.

“When a mine closes, it lays off thousands of workers. This devastates communities that rely only on the mine for their economic output. UGES would create a few vacancies as the mine would provide energy storage services after it stops operations,” says Julian Hunt, a researcher in the IIASA Energy, Climate, and Environment Program and the lead author of the study.

“Mines already have the basic infrastructure and are connected to the power grid, which significantly reduces the cost and facilitates the implementation of UGES plants.”

Seemingly so. The study reckons other energy storage methods, like batteries, lose energy via self-discharge over long periods. The energy storage medium of UGES is sand, meaning that there is no energy lost to self-discharge, enabling ultra-long time energy storage ranging from weeks to several years.

The investment costs of UGES are estimated at $1 to $10 per kWh and power capacity costs of $2,000/kW. The technology is estimated to have a global potential of 7 to 70 TWh, with most of this potential concentrated in China, India, Russia, and the US, but Australia too has scope.

Contrast: a recent study by BNP Paribas Asset Management suggests that decommissioning redundant and end-of-life energy, mining, industrial, waste management and shipping assets could cost at least $8tn over the coming decades. The energy transition may well hasten and accelerate these numbers.

With companies acknowledging the acceleration of the energy transition, decommissioning work is brought forward, raising the current estimates of the associated costs. Costs also often rise significantly over time. For example, one mining company saw its closure provision rise almost fivefold amid cost revisions – from A$16m in 2008 to A$805m in 2015.

In worst case scenarios, without planning, oil and gas, mining, power and other companies may not be able to meet their decommissioning costs with free cash flows due to revenue volatility, warns BNP. In Australia, mining decommissioning represents 29% of total decommissioning costs in 2023, some $37bn, behind only oil and gas.

“To decarbonise the economy, we need to rethink the energy system based on innovative solutions using existing resources. Turning abandoned mines into energy storage is one example of many solutions that exist around us, and we only need to change the way we deploy them,” concludes Behnam Zakeri, study co-author and a researcher in the IIASA Energy, Climate, and Environment Program.

More research has found the Australian landscape is badly affected by abandoned mines that pose environmental, public health and safety risks. The paper argues that while the mining industry has undoubtedly made significant contributions to the Australian economy over time, at least 80,000 sites remain inactive and unrehabilitated, posing a range of environmental, public and health and safety risks.

Efforts to ensure progressive rehabilitation throughout the life of mining operations and to promote an effective transition to post-mining landscapes are critical for Australia to achieve its goals of being a world leader in environmental stewardship and mineral resource governance.

Companies like Green Gravity have already rolled out UGES demonstrators, headed up by ex-BP exec Mark Swinnerton. Now chief exec at Green Gravity, he said having a physical model to demonstrate the UGES idea was crucial in garnering support from investors and government.

He said: “This is a huge step in our technology, thinking how we can make it commercial quickly, and part of that is building a test facility.”

Mark Swinnerton said for UGES to succeed, it would need buy-in from a number of different sectors, including mining, energy and government. Whitlam MP and Assistant Treasurer Stephen Jones said the project could have a significant impact on the State's renewable energy needs and the federal government was keen to play its part.

“I'm very keen to see this project take off. This has the capacity throughout New South Wales to provide around about 15% of the storage needed over the next 20 years, so I'm keen to see if it does stack up,” he said.