900 pits, 77 countries, 30 TWh Mine-to-pumped-hydro projects in development, with global brownfield potential.
Closed mines can offer many of the right ingredients for pumped storage hydro. But as Kidston demonstrates, geology is a critical factor in whether a project succeeds. A former mine can’t be transformed into energy infrastructure until there’s evidence that a scheme can be constructed and operated for its design life within the geological conditions of the site. A second life for legacy mines The growing interest in mine repurposing comes amid surging electricity demand¹ and a broader structural shift in power systems. As demand for both electricity and renewable generation expands, grids need storage that can absorb electricity when supply is high and release it when demand rises. Pumped storage hydropower has now surpassed 200 GW of installed capacity worldwide and the global development pipeline has reached 621 GW across all stages of development², with new projects being explored as countries look for storage options to balance higher levels of wind and solar. As the grid adds more variable renewable generation, that role is likely to grow. Three times built, and counting Global pumped storage hydro — installed capacity vs development pipeline (GW)
Legacy mines are one possible route to providing that balance. Pumped hydro needs elevation difference and an old mine pit can provide that over a short distance, effectively creating a man-made cliff. That can be especially valuable in flatter regions where natural topography is limited. Mine sites may also have access roads, existing water-management arrangements, disturbed land with low environmental value and in some cases, nearby grid or transmission infrastructure. Kidston is not the only site where old mines are being repurposed for energy infrastructure. Other mine-to- pumped-hydro projects are being studied or developed at a former slate quarry in Glyn Rhonwy, Wales³; at a former iron mine in Marmora, Ontario⁴; and at a closed coal mine in Glenmuckloch, Scotland⁵. More such projects seem likely as well. Researchers have identified more than 900 potential brownfield pumped hydro sites across 77 countries, with combined potential storage of 30 TWh⁶. Technologic and geologic hurdles But it’s not as simple as just identifying old mines with potential. Mine pits are usually designed for operational lives of a few decades at most. Pumped hydro infrastructure, on the other hand, may need to operate for at least 100 years or more. That timeframe adds a major challenge to adapting a mine for pumped hydro. It’s not enough that a pit already exists, or that it has a useful elevation difference. Engineers must determine if pit walls can remain stable over a much longer time-span; whether tunnels, caverns and other underground works can be located in competent, dry rock that won't bend or break under stress; and how groundwater will behave as reservoir levels rise and fall through repeated operating cycles.
Scotland Glenmuckloch project
Wales Glyn Rhonwy project
Ontario Marmora project
Queensland – Kidston project – Mount Rawdon* project
* Shelved project.
In development*
621
Built for decades, asked to last a century
Operating
200+
Water itself presents significant uncertainty. Mineralised areas are often fractured and altered, which can create seepage pathways. Old boreholes, faults, hidden workings or backfilled areas can also move water in unexpected ways. Mine water may have interacted with acid-forming minerals, creating durability concerns. These uncertainties are among the main barriers to converting old mines into pumped hydro projects. Properly de-risking a site means reconstructing enough of its geology, hydrology and mining history to decide whether it can truly be a viable long-life project. The Kidston conversion Kidston shows what de-risking can look like in practice. It didn’t start as a blank slate, but it also didn’t begin with a complete technical record. Mining operations had ceased some two decades earlier and of the information that was available, much of it had been created for mineral exploration and mining, not to support the design of long-life energy infrastructure. Because of that, the design work became a form of forensic reconstruction. Geologists synthesised decades of disparate data, from historical borehole files, exploration plans and gold-grade logs to scanned pre-mining topography, aerial photographs and modern drone surveys, to construct a unified 3D geological model of the site.
Pumped storage is no longer a niche asset class. The pipeline is roughly three times the size of everything built to date. * Not yet real.
Design life of a mine pit vs a pumped storage scheme.
Mine pit's operational life
Pumped hydro asset's expected life 20–40 years
100+ years
32 | GHD | Nexus Magazine
Nexus Magazine | GHD | 33
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