As Australia transitions to a high-renewables electricity system, the role of long-duration energy storage is becoming increasingly central. While lithium-ion batteries have transformed short-duration firming, the next phase of the energy transition will require storage solutions capable of delivering longer discharge durations, minimal degradation, and strong sustainability credentials.
Green Gravity, an Australian clean technology company, is developing a gravitational energy storage system (GESS) that repurposes disused mine shafts into long-duration storage assets. We spoke with Founder and CEO Mark Swinnerton about how the technology works, why legacy mine shafts present a unique opportunity, and how gravity storage could support Australia’s evolving energy market.
About
Mark is the Founder and Chief Executive Officer of Green Gravity and has over 25 years of global experience in the mining, metals, manufacturing and logistics sectors.
Green Gravity is an Australian renewable energy storage company founded in 2020. Headquartered in New South Wales, the company was established to commercialise gravitational energy storage technology using repurposed legacy mine shafts. Green Gravity works with mining companies, engineering partners and research institutions to develop scalable, sustainable long-duration storage solutions for domestic and international energy markets.
Gravity Energy Storage Explained: A New Approach to Long-Duration Storage
Why is long-duration storage becoming critical in Australia?
Australia has made significant progress in deploying wind and solar generation, but as renewable penetration increases and coal-fired power stations progressively retire, the system challenge shifts from building generation to maintaining reliability. The grid is becoming more weather-dependent, and the variability of supply needs to be balanced over longer timeframes. Short-duration battery energy storage systems (BESS) have proven highly effective in managing intra-day volatility and providing fast frequency response. However, as the energy mix continues to evolve, the system increasingly requires storage capable of delivering sustained discharge over longer periods.
Long-duration storage allows excess renewable energy generated during low-demand periods to be stored and dispatched when the system needs it most: for example, during overnight peaks or extended low-renewable events. From our perspective, the next phase of the transition requires storage that is durable, sustainable and economically scalable.
How does Green Gravity’s system work in practice?
Our system converts electrical energy into gravitational potential energy by lifting heavy weights within an existing vertical mine shaft. When renewable energy is abundant, we use electric motors to raise engineered weights. When the grid requires power, those weights are lowered in a controlled manner, driving regenerative motors to generate electricity. Consider the mechanics as similar to pumped hydro, but rather than moving water between two dams, Green Gravity requires much less space by using far denser materials.
The concept draws on simple physics, but what makes it compelling is the use of existing infrastructure. A deep vertical mine shaft provides the height necessary to store meaningful amounts of energy. By repurposing that shaft, we avoid constructing large new structures and significantly reduce environmental impact.
Unlike batteries, there are no chemical cells that degrade over time. The system relies on well-understood mechanical components, such as hoisting systems, motors, control systems, which can deliver long asset life with relatively predictable maintenance requirements. Green Gravity can deliver equipment life three to four times longer than a chemical battery.
Why focus on legacy mine shafts?
Australia has a vast inventory of legacy mine shafts, many of which represent environmental and financial rehabilitation liabilities. There are nearly 100,000 shafts in Australia, presenting us with an opportunity to transform those liabilities into clean energy infrastructure.
A suitable mine shaft provides vertical depth, structural integrity and proximity to grid infrastructure. By leveraging existing assets, we reduce construction complexity and resource requirements compared with building entirely new storage facilities.
There is also a regional development dimension. Many mining communities face economic transition as traditional resources decline. Repurposing mines into renewable storage infrastructure can support local employment, engineering capability and long-term economic resilience. This is a practical example of circular economy thinking applied to energy infrastructure.
How does gravity storage compare with other long-duration technologies?
Each storage technology has a role to play. Battery energy storage systems are well suited to short-duration applications and fast response. Pumped hydro offers very large-scale storage but requires specific geography and significant water resources.
Our gravitational system is differentiated by three core attributes: sustainability, longevity and scalability. There are no hazardous chemicals, no water reservoirs and minimal degradation over time. Mechanical systems can operate for decades, and because we are reusing mine infrastructure, the environmental footprint is comparatively low.
For longer duration, particularly beyond typical 4-hour battery applications, gravitational storage can offer a competitive levelised cost of storage. Importantly, it provides dispatchable capacity without the lifecycle challenges associated with chemical batteries.
What are the key development and engineering considerations?
Site selection is critical. Shaft depth, diameter, structural integrity and access all influence project design. Detailed engineering assessments are required to confirm suitability and ensure safety.
From a construction perspective, we are working with established engineering partners and applying proven mining hoisting technologies in a new configuration. Because we are adapting existing infrastructure rather than building entirely new dams or reservoirs, the development footprint can be relatively contained. Importantly, this approach supports stronger community buy-in, as it focuses on repurposing already disturbed land, rather than developing greenfield or pastoral sites, and aligns with local expectations around land use and post-mining transition outcomes.
How does gravitational storage align with ESG priorities?
Sustainability is central to our value proposition. Our system avoids the use of critical minerals typically associated with chemical batteries and does not generate hazardous waste at end-of-life. The mechanical components are durable and maintainable over decades.
Additionally, our parts can be locally sourced. Unlike lithium batteries, which are developed using water intensive processing, combined with rare minerals and require a long global supply chain for assembly.
Repurposing legacy mine shafts supports environmental remediation objectives while contributing to clean energy infrastructure. It also provides social benefits in regions historically dependent on mining. This approach supports regional employment and investment by building on existing mining capability and enabling new economic activity in transitioning communities. We see gravitational storage as not just a technical solution, but a transition solution that links Australia’s industrial past to its renewable future. In addition, by smoothing variability in renewable generation, gravitational storage can help optimise the use of existing transmission infrastructure and, in some cases, reduce or defer the need for additional network expansion.
What progress has Green Gravity made toward deployment?
We have progressed our technology through a structured development pathway, including the commissioning of the Gravity Lab in Port Kembla in 2023. This purpose-built above-ground facility, which is approximately 15 metres tall, operates as an integrated pilot plant and has been used to validate key physics and engineering outcomes prior to deployment in underground environments.
We are now progressing from design to demonstration. We have entered into a binding agreement to trial our gravitational energy storage system at the Russell Vale coal mine in New South Wales, which has not operated since 2015. The trial is being run at depths of up to 400 metres, providing crucial data for scaling the technology.
The demonstration phase represents the first global trial of its kind. It allows us to prove the technology in a real-world environment, confirm operating characteristics and build confidence with investors, partners and regulators.
Beyond the demonstration project, we are actively exploring additional sites and scaling opportunities. The modular nature of the system allows capacity to be scaled depending on shaft depth and site characteristics. Commercial application of Green Gravity’s gravitational energy storage technology is expected to deliver increments of up to 10 megawatts (10 MW) of between 8 and 20 hours of duration at individual mineshafts.
What needs to happen next for large-scale deployment?
Clear market signals recognising the value of long-duration and firm capacity will be important. As reliability mechanisms and system service markets evolve, investment will be influenced by whether market frameworks appropriately value dispatchable capacity, duration and asset longevity.
Our immediate focus is delivering successful demonstration projects, advancing commercial partnerships and building commercial partnerships for future deployments across suitable mine sites. At Green Gravity, we are positioning gravitational storage as a long-life, mechanically durable solution that can contribute to Australia’s evolving energy mix by providing durable, sustainable long-duration storage to support a resilient, low-emissions grid.
The Hamilton Locke team advises across the energy project life cycle – from project development, grid connection, financing, and construction, including the buying and selling of development and operating projects. For more information, please contact Matt Baumgurtel.
