Converting mines into hydro-powered batteries
Scattered across the globe, abandoned mines often lie forgotten, gaping scars of a bygone industrial era. But these deep, empty shafts are now being reimagined as powerful tools in the fight against climate change. Engineers and energy innovators are exploring how to convert old mines into “giant water batteries,” using a method called mine-based pumped hydro energy storage, or PHES. This approach could transform environmental liabilities into vital energy assets, helping stabilize the power grid, support renewable energy expansion, and breathe new life into struggling former mining communities.
Renewable energy has made remarkable strides, but it comes with a significant challenge: the issue of intermittency. Solar panels only generate electricity when the sun is shining. Wind turbines only spin when there’s wind. Meanwhile, the power grid must deliver a steady supply of electricity, regardless of weather or time of day. Although batteries, such as lithium-ion systems, can store energy, they are expensive for long-duration use and may not scale well for the entire grid. As the world transitions toward cleaner energy sources, there’s a pressing need for more robust, long-term storage solutions that can fill in the gaps when solar and wind power dip.
This is where mine-based pumped hydro steps in. The idea is simple yet elegant. Think of it as a massive battery that stores energy in the form of water at elevation. A mine, with its vertical depth, naturally serves as the lower reservoir. When renewable energy is plentiful—such as on a sunny or windy day—it powers pumps that move water up to a higher reservoir, which may be a natural elevation or an artificial basin. When the energy is needed, the water is released to flow back down through turbines, generating electricity as it descends. This system is known for its high efficiency, often between 70 and 85 percent, and can last for decades with minimal degradation—something chemical batteries struggle to match. By using existing mine shafts, developers avoid the cost and environmental impact of excavating new underground storage spaces.
The advantages of repurposing mines in this way are significant. First, it contributes to environmental cleanup. Abandoned mines can pose ongoing environmental hazards, such as soil and water contamination. Turning these sites into energy storage facilities gives them a second life while reducing risks. Unlike traditional pumped hydro systems, which require damming rivers and flooding large areas, mine-based PHES utilises disturbed land without major landscape alterations. It also supports renewable energy integration by smoothing out fluctuations in supply, reducing the need for fossil fuel backup power, and lowering greenhouse gas emissions.
Economically, these projects can bring hope to regions hit hard by the decline of the mining industry. Building and operating PHES systems creates jobs in engineering, construction, and maintenance. Many of the logistical components—such as roads, transmission lines, and access to water—are already in place from mining operations, thereby reducing development costs. In areas where mining was once the economic backbone, energy storage can offer a new, sustainable industry that benefits both workers and the wider community.
From an energy perspective, mine-based PHES improves grid reliability and resilience. It provides a form of dispatchable power—electricity that can be delivered on demand, which is crucial when dealing with variable renewable sources. As more solar and wind power comes online, the need for such flexible storage options will only increase. Mine-based systems provide the scale and duration necessary to maintain grid stability during periods of high demand or low renewable energy generation.
Of course, challenges remain. The geological integrity of old mines must be assessed to ensure safety, and water quality needs to be monitored and managed. Regulatory hurdles, such as environmental permitting, can delay projects. And while the costs are often lower than building new hydro systems from scratch, the initial investment is still considerable. Yet, despite these obstacles, interest in mine-based PHES is growing, with pilot projects in countries such as Germany, Australia, and Canada demonstrating what is possible.
Converting abandoned mines into clean energy storage facilities represents a remarkable fusion of past and future. With creativity and engineering, these relics of extraction can be transformed into engines of sustainability. As the world moves away from fossil fuels, these underground spaces may once again serve a critical role—this time, in building a cleaner, more resilient energy future for all.
