The global energy transition depends on rapidly integrating variable renewables such as solar and wind. These sources already account for record shares of generation in multiple regions, but their variability creates challenges of balancing and reliability. Hydropower is uniquely positioned to provide the flexibility, storage and stability required. Pumped storage represents more than 90 per cent of global storage capacity, demonstrating the sector’s systemic importance. Many hydro plants are ageing, with nearly 600 GW of global capacity exceeding 30 years of operation, and 400 GW older than 40 years. Ageing infrastructure undermines efficiency and increases risks of failure, just as demand for system services accelerates. Modernization is not simply maintenance, but a strategic necessity.
By Cecilia Tortajada and Asit K. Biswas, 2025. Article published in World Atlas of Hydropower & Dams.