Loss-induced performance degradation mechanisms in vertical-axis wind turbines: A comparative failure-based study to identify the optimal configuration

Abstract

Vertical-axis wind turbines often exhibit performance degradation due to aerodynamic and mechanical loss mechanisms that restrict their large-scale deployment. This study investigates the dominant loss pathways that lead to energy shortfall in VAWTs through a comparative assessment of two conventional configurations (Savonius and H-Darrieus rotors) and an eccentric air-activated hybrid vertical-axis wind turbine (AAHT) using real wind data of a coastal site in eastern India. The methodology quantifies loss contributions arising from negative aerodynamic drag, bearing friction, startup inefficiency, static inertia hysteresis, and rotor speed latency under wind transients. Two dimensionless diagnostic indices are introduced: Startup Failure Exposure Index, normalizing startup-related energy loss against available wind energy, and Mechanical Loss Exposure Index, normalizing mechanical dissipation against generated mechanical power. Sensitivity analysis is performed to assess the robustness of degradation trends to aerodynamic and mechanical parameter uncertainty. The results reveal that the negative drag causes the most severe performance degradation in conventional VAWTs, accounting for power losses of 183.75 W in the Savonius rotor. In contrast, this loss is restricted to 22 W in the AAHT through the controlled blade exposure mechanism. Frictional losses (0.72–2.66 W) and inertia-related energy losses (0.046–0.067 Wh) are further compounding efficiency degradation. Although Savonius turbines are attributed with superior self-starting ability, they suffer substantial cumulative losses during steady operation. The analysis demonstrates that minimizing these failure mechanisms can significantly improve energy yield: AAHT can achieve an annual yield of 499.07 kWh compared to 405.73 kWh and 243.57 kWh for H-Darrieus and Savonius rotors, respectively. The outcome of the investigation provides a failure-analysis-based framework for diagnosing performance-limiting elements in VAWTs and offers design-level insights for reducing loss-induced degradation in small-scale wind energy systems.