Harnessing hydrokinetic energy from hydropower plant tailraces: A review of technological advances, feasibility studies, and prospects

• This study reviews and analyzes hydrokinetic systems in tailraces. • Limited research exists on hydrokinetic systems in hydropower tailraces. • Tailraces offer fast currents and minimal environmental impact for hydrokinetic. • Strengths include boosted generation, using existing infrastructure, environmental. • Weaknesses include flow resistance, high costs, and limited operational data. This study presents the first narrative review dedicated to hydrokinetic energy recovery in the tailraces of conventional hydropower plants, synthesising literature from 2009–2025. Tailraces offer unique deployment advantages, fast currents, existing infrastructure, and stable hydraulic conditions, yet remain laregely underexplored in both academic and industrial contexts. By consolidating a globally diverse body of research covering multiple geographical settings, turbine technologies, operational regimes, and methodological approaches, the review delivers a comprehensive perspective on this niche but promising application. It introduces a tailored nonlinear formulation linking upstream hydropower discharge to tailrace velocity and hydrokinetic power output, enabling integrated modelling of hybrid hydropower-hydrokinetic systems. A comparative classification framework is developed to organise deployments by site configuration, turbine type, grid integration strategy, and environmental interaction. An eight-step feasibility assessment methodology is proposed, integrating technical, environmental, economic, and policy dimensions, and is complemented by a SWOT analysis positioning tailrace hydrokinetics within broader renewable energy transitions. Literature review indicates capacity factors ranging from approximately 18 % in seasonal low-flow channels to over 45 % in regulated tailraces, with potential energy gains of up to 27 % above baseline hydropower generation. As reported in scientific articles the estimated generation potential from European tailraces alone is 2.4 TWh per year, although multi-region case studies demonstrate opportunities beyond Europe. The key challenges include flow-resistance impacts on upstream head, high capital costs, and regulatory gaps, while opportunities arise from policy support, technological advancements, and synergies with existing hydropower assets. By consolidating dispersed data and providing quantifiable benchmarks, structured feasibility guidance, and strategic findings, this review offers a unified reference for researchers, engineers, and policymakers, and aims to accelerate the technically robust and sustainable deployment of hybrid hydropower-hydrokinetic systems.