Battery Energy Storage Integration to Enhance Reliability and Reduce Start-up Stress in Hydropower Units: Case Study of AHE Drăgan–Iad

Abstract Hydropower plants are increasingly required to provide fast-response balancing services to compensate for the variability of wind and solar generation. However, frequent start-up and shutdown cycles impose severe mechanical and hydraulic stresses, reducing the mean time between failures (MTBF) and increasing unplanned outages. This paper investigates the Drăgan–Iad Hydropower Development (Romania), analyzing Reliability–Availability–Maintainability (RAM) indicators, vibration and cavitation monitoring, and the techno-economic potential of integrating Battery Energy Storage Systems (BESS). Results show that BESS can reduce torque peaks by 20–40%, lower cavitation intensity by 25–30%, and extend MTBF by 13–15%. Economic evaluation indicates annual savings of EUR 50,000–90,000 from avoided outages, with a payback period of 5–6 years. Beyond technical benefits, hybrid hydro–BESS systems contribute to the sustainable modernization of hydro-technical infrastructures, prolong equipment and structural lifetime, and improve grid flexibility in renewable-dominated systems.