The Role of Hydraulic Turbines in the Energy Transition: A Systematic Review of Methods for Evaluating and Optimizing Hydropower Plant Operation

Hydropower plants remain strategic assets for grid stability and decarbonization, with hydraulic turbines governing conversion efficiency, reliability, and environmental performance. This systematic review synthesizes recent methodologies for evaluating and optimizing turbine operation and maintenance to enhance efficiency, reduce impacts, and extend service life. Following a PRISMA-aligned protocol, studies published between 2020 and 2025 were screened across Web of Science and Scopus, using predefined eligibility criteria and a two-stage selection process. The resulting evidence was thematically analyzed across three domains: lifecycle and circular-economy-oriented refurbishment strategies; digitalization and predictive maintenance approaches; and environmentally optimized operating regimes. Of the 115 screened records, 37 met the inclusion criteria. Findings indicate that predictive monitoring, data-driven maintenance, and turbine selection tailored to local hydrology can significantly improve energy performance while reducing operation and maintenance costs. The literature also highlights the importance of ecological flow compliance and reduced aquatic impacts. Complementary case studies from Nepal, Switzerland, Germany, Portugal, and Romania illustrate regional challenges and modernization pathways. Overall, the review underscores the need for integrated, multi-objective turbine management that aligns techno-economic, lifecycle, and ecological considerations to support hydropower competitiveness within the energy transition.