Storage innovation: unlocking mines, oceans and reservoirs

As Europe races to integrate rapidly growing shares of wind and solar, the need for long-duration, flexible storage is outpacing what batteries alone can deliver. Pumped storage hydropower, which provides more than 90% of global electricity storage remains the only proven, large-scale option at multi‑hour to multi‑day durations. However, greenfield development faces increasing constraints. Europe has a vast quantity of disused or underutilised assets, from abandoned open‑pit mines and coalfields to existing reservoirs and legacy hydropower schemes that could be converted into modern pumped storage plants, often with access to existing grid and transport infrastructure.  

This session will explore how brownfield development can unlock the next wave of pumped storage by repurposing mines, reservoirs and conventional hydro stations into closed‑loop and hybrid PSH systems, reducing environmental impact while revitalising industrial and rural regions. It will also examine emerging concepts such as marine, also known as seawater  pumped storage, which expands the geographical application for pumped storage where inland sites, or freshwater, may be  scarce. Together, these innovative solutions point to a new generation of pumped storage projects designed around circular land use, reduced CAPEX, and system integration needs.  

Session objectives

• Showcase real-world brownfield PSH projects in mines, reservoirs and legacy hydro sites, highlighting technical configurations and performance.
• Assess environmental, social and permitting benefits and challenges of repurposing existing sites versus greenfield developments.
• Explore innovative concepts such as seawater and coastal PSH and their potential role in power systems with limited conventional sites.
• Discuss business models, regulatory frameworks and financing approaches that can scale brownfield and marine pumped storage as part of long-duration storage strategies.