<b>Unlocking Pumped</b> <b>H</b><b>ydroelectric Storage Potential for</b><b> Electricity</b><b> Decarbonization</b>

Large-scale energy storage is essential for balancing wind and solar variability in variable renewable energy (VRE) systems. Pumped hydroelectric storage (PHS) is the most mature and scalable long-duration storage solution^1-⁶. We assessed PHS feasibility for VRE support using a unified high-resolution framework that identifies open-loop sites linked to lakes and 2.89 million rivers, as well as low-impact closed-loop sites. Our assessment provides an upper-bound estimate of global PHS resources, with a capacity estimated at 28.85 ± 3.75 trillion kWh, sufficient to meet current global electricity demand and contributes to a fully renewable grid to support electricity decarbonization goals. Addressing spatial mismatches between electricity supply and demand requires long-distance transmission and grid enhancements, enabling resource-rich regions to support electricity decarbonization in other geographical areas. Our findings provide a quantitative foundation for energy planning, emphasizing the need for strategic investment in long-term storage, transmission infrastructure, and supportive policies. Unlocking PHS potential can further advance renewable energy integration and accelerate global electricity decarbonization.