Spotlight | Mines to megawatts Mine Storage CEO Fredrik Olrog discusses the technical realities,
commercial drivers and global scalability of repurposing underground mines for long-duration pumped storage hydropower
AS LONG-DURATION ENERGY storage moves from policy ambition to engineering necessity, the challenge facing the hydropower sector is no longer technological capability but deployability. Europe’s hydropower industry has increasingly warned that without large-scale storage infrastructure, renewable expansion will lead to curtailment, price instability and growing system risks. Pumped storage hydropower, which today accounts for more than 90% of global electricity storage capacity, is therefore emerging as a critical enabling technology for power system resilience and decarbonisation. Yet despite its maturity, expansion remains constrained by geography, permitting complexity and capital intensity. Suitable sites with the required topography are limited, while environmental considerations and long development timelines further restrict new projects. Against this backdrop, alternative approaches that
The Vånga project is located in the Swedish electricity price area SE4 that is currently struggling with volatile electricity prices
extend the applicability of pumped storage without fundamentally altering its operating principles are gaining attention. Mine Storage is one such developer, advancing a model based on repurposing decommissioned underground mines into closed- loop pumped hydro systems. By shifting the spatial requirements of storage from natural elevation to engineered vertical shafts, the company aims to unlock new locations for deployment while giving existing, idle infrastructure new purpose. In an interview with International Water Power & Dam Construction, CEO Fredrik Olrog outlines how this concept translates into practical engineering, project configuration and commercial strategy, and where it may sit within the evolving energy storage landscape.
Engineering constraints and
design optimisation Mine-based pumped storage introduces a fundamentally different design envelope compared to conventional surface schemes. Rather than shaping reservoirs and waterways to suit hydraulic requirements, engineers must work within the constraints of pre-existing underground geometry. “Mine-based systems have less geometric flexibility,”
Olrog says, noting that the use of existing shafts and underground structures requires careful handling of hydraulics and construction sequencing. Vertical shafts are central to the concept,
providing the hydraulic head required for energy storage. However, they also introduce efficiency penalties that are less pronounced in conventional waterways. Frictional losses along shaft walls, as well as turbulence at transitions and interfaces, must be actively managed through design optimisation. “Vertical shafts with naked rock surfaces introduce
potential efficiency losses, both from friction and turbulence,” Olrog says. “We manage that through shaft diameter optimisation and smooth linings and high-quality electromechanical designs” Despite these constraints, overall system performance remains comparable to conventional pumped storage. “The overall efficiency remains around 70 to 80%” he notes, placing mine-based systems within a competitive range for round-trip efficiency. The process of converting a mine into a functional
storage system involves multiple layers of intervention. Existing shafts typically require rehabilitation, including
10 | June 2026 |
www.waterpowermagazine.com
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