Long-term deployment of marine current turbines: a review of biofouling effects on performance degradation, mitigation strategies and techno-economic impacts

Marine current turbines (MCTs) are a promising technology for predictable renewable energy generation, but their long-term performance is significantly affected by the harsh marine environment. Among the various degradation mechanisms, biofouling is one of the most critical, as it increases surface roughness, modifies hydrodynamic loads, reduces energy conversion efficiency, and raises operation and maintenance costs. This review critically examines the effects of biofouling on MCT performance by integrating hydrodynamic, biological, operational, and techno-economic perspectives. Existing experimental, numerical, and field studies indicate that moderate biofouling typically reduces the power coefficient by 10–20%, while severe natural colonisation may lead to power losses exceeding 40%, with the magnitude of degradation depending on fouling morphology, turbine configuration, installation conditions, and operating strategy. The effectiveness and limitations of current mitigation approaches, including antifouling and foul-release coatings, adaptive tip-speed-ratio control, cleaning schedules, and component-specific maintenance strategies, are systematically discussed. A key contribution of this review is the identification of the gap between site-specific biofouling observations, predictive growth modelling, and turbine performance assessment. To address this limitation, an integrated framework is proposed that combines local biofouling monitoring, hydrodynamic modelling, and techno-economic indicators to support lifecycle performance assessment. The analysis highlights that biofouling should be considered not only as a surface degradation phenomenon but also as a key lifecycle driver influencing turbine design, maintenance planning, annual energy production, and the economic viability of tidal energy systems.