On the Self-Start of Darrieus Vertical-Axis Wind Turbines: A Review of Promising Strategies

Self-start of lift-type Darrieus vertical-axis wind turbines remains one of the main obstacles limiting their wider application, especially at low wind speeds and low Reynolds numbers. This review examines the physical basis of the self-start problem and critically discusses the main aerodynamic and design strategies proposed to improve start-up behaviour. Particular attention is paid to the distinction between the mere initiation of rotation and true self-start, understood as the autonomous acceleration of the rotor from rest to its operating regime. The reviewed approaches include changes in rotor solidity, blade-shape modification, auxiliary blades, slot-based flow control, and active or passive pitch-control systems. The available studies show that increasing solidity generally improves low-TSR torque and facilitates start-up, but usually at the expense of lower peak efficiency. Blade-shape optimization, auxiliary blades, and flow-control concepts may improve start-up-related aerodynamic characteristics; yet, the reported evidence often concerns only motion initiation or low-TSR performance rather than full passive self-start. Pitch-control mechanisms appear to be the most direct way to reduce negative torque regions, but they introduce additional mechanical complexity. Overall, no reviewed solution can yet be regarded as a universally reliable passive self-start method for Darrieus turbines operating under low-wind-speed conditions.